NAME __________________________________ NOTES: UNIT 9 (2): MOLECULAR POLARITY AND
INTERMOLECULAR FORCES OF ATTRACTION
HMMM, looks like there’s some serious theoretical work on the horizon!
Okay, We are done with: * metallic bonds and the metallic elements
* ionic bonds and ionic compounds
* covalent bonds ….. but we’re NOT done with molecules
We must now focus on why covalent bonding in molecules creates chemical and physical phenomena which
are different from those found in ionic compounds.
This natural progression of thought leads us to MR #5:
The species radii and strength of the ionic bond, determine the physical characteristics
of ionic compounds.
The number of delocalized electrons of a metal is one important factor in comparing the
physical properties of pure metals.
However, the physical properties (e.g phase, melting point, vapor pressure, solubility etc) of
molecular compounds are due to the type and in the strength of intermolecular forces
of attraction which exist between molecules. The type and strength of intermolecular force
depends upon:



the molecular geometry
extent or level of the distribution of opposite charge across the molecule (e.g.
dipole moment)
molecular mass
*****************************************
Think about it: You know all about sucrose (table sugar C12H22O11) and table salt (NaCl). They both dissolve
in water ... but one is a nonelectrolyte and the other is an electrolyte.
Almost all of the phenomena demonstrated by sodium chloride (salt) can be explained by the electrostatic forces
of the actual ionic bond (positive charges attracting negative charges).
But, covalent bonds don’t exert the same level of electrostatic force. They are created via physical
manipulation (hybridization) of the orbital spaces around two nuclei. Clearly, there is a discrete difference
between molecular compounds and ionic compounds.
619
Have you ever wondered why molecules of a covalent substance don't go flying off into space as a gas
or how can we have solid or liquid molecular materials?
Substances composed of discrete molecules exhibit a wide range of melting and boiling points. There
must be something then, some type force between the molecules, that reinforces the bonds holding the
atoms of a molecule together. This force must act between the molecules and must be different in its
generation and effect from bonds.
When it comes to molecules, the challenge is to develop an understanding that covalent bonds may
be polar and nonpolar and that the *resulting molecules may also be classified as polar and
nonpolar, but for reasons that are different from the bond types.
As written in the NYS 2001 core document:
Atoms and molecules are in constant motion. Chemical bonding between atoms involves energy and the
interaction of electrons with atomic nuclei. Intermolecular attractions, which may be temporary, occur when
there is an asymmetric (uneven) distribution of charge.
Intermolecular forces created by the unequal distribution of charge result in varying degrees of attraction
between molecules. Hydrogen bonding is an example of a strong intermolecular force.
Physical properties of substances can be explained in terms of chemical bonds and intermolecular forces. These
properties include solubility, melting point, boiling point etc..
Okay my first year student ... Look at issue this way:
Covalent Bonds are INTRAmolecular forces in which at least 1 pair of electrons is attracted to
two different nuclei, with a relatively balanced force distribution in terms of repulsion and attraction.
INTERmolecular forces are far weaker forces of repulsion and attraction that exist BETWEEN (inter-)
molecules. They are due to the evolved partial charges (created at bonding) of the various species of
molecules.
inTRA-molecular force (bond)
𝛿+
𝛿-
inTER-molecular force
𝛿-
𝛿+
620
GIMME’ A METAPHOR
A BOND is like…
An IMF is like…
http://prayerwarriors.wordpress.com/2009/10/06/dont-compromise-by-elaine-davenportwednesday-october-6-2009/crowd-of-people/
a chorus line
http://www.niams.nih.gov/health_info/sports_injuries/
a body joint
a crowd
a hook and eye clasp
http://lagirlsweetea.blogspot.com/2010_07_01_archive.html
http://tinyurl.com/m29mu65
http://addisonlibrarycs.wordpress.com/2012/04/04/love-legos/
http://mychannel957.com/
Snapped together Legos
a soccer game
.... Which is stronger? (bond or IMF)
.....Which is responsible for building a single molecule? (bond or IMF)
.....Which is responsible for the phase of a substance with trillions of molecules? (bond or IMF)
621
XII) Intermolecular Forces of Attraction: (also called, collectively as van der Waals Forces)
Name of IMF
London
Dispersion
Forces
Dipole
Attraction
Hydrogen
Bonds
(classical
interpretation)
Conditions
between any
molecule (polar or
nonpolar with
electron clouds
Comments
exist to to the ability of the electron clouds to be polarized.
A collection of electrons on one species creates a somewhat more
negative volume, inducing electrons on a second species to repel
away, thus evolving a somewhat more positive volume of space.
This is the weak IMF. And then as the electrons continue to move,
it changes, and is gone, only to be re-established.


The only IFA between nonpolar molecules

The shape of the molecule affects the strength (long
aliphatic molecules have stronger LDF than chunkier
molecules (due to surface area issues …better contact in the
longer molecules)

Molecules with greater molecular masses have stronger
LDF. (due to the relationship between the number of
protons and electrons …more protons = more electrons,
and thus greater chances for polarization in the larger
electron cloud)

Cumulative in effect. They are the weakest of the IMF, but
the sum of their effect is in many cases makes them the
major force of attraction and explanation of physical
properties.
between any
molecules with a
permanent dipole
(polar molecules)
In addition to LDF, dipole attractions exist between polar
molecules. The positive end of one molecule attracts the negative
end of a second molecule.
a special form of
dipole attraction
In addition to LDF, hydrogen bonds (hydrogen bonding) exists
most strongly between molecules which have hydrogen bonded to
fluorine, oxygen or nitrogen, and any other second molecule with
F, O, N
unusually strong
… up to 5% of a
covalent bond in
energy (strength)
These matter when the species are close to each other
A “super-dipole-attraction” due to the incredibly large
electronegativity values of F, O, N coupled to their very small radii.
This results in a charge density or concentration which magnifies
the dipole attraction.
622
Recall a part of Big Idea #5: … However, the physical properties (e.g phase, melting point, vapor
pressure, solubility etc) of molecular compounds are due to the type and in the strength
of intermolecular forces of attraction which exist between molecules. The type and
strength of intermolecular force depends upon:




the molecular geometry
extent or level of the distribution of opposite charge across the molecule (e.g. dipole moment)
molecular mass
A) IMF FACTS:
Intermolecular forces of attraction vs. Bond Types
1) FactIMF: are between * molecules
.... covalent bonds link * atoms of a molecule
2) FactIMF: are the results of bonding: not bonds themselves. No new e- are transferred or
shared. These are the attractions between the partial charges on different molecules.
3) FactIMF: are * much weaker
than covalent bonds
4) FactIMF: IMF are generated as electrons move within a molecule
5) FactIMF: help explain molecular solubility and PHASE (melting point, density, boiling point)
Molecules in the gas phase exhibit * weak
IMF between the molecules
Molecules in the solid phase exhibit * strong
IMF
6) FactIMF: are of various strengths ... some IMF are stronger than other IMF
London Disperion Forces are found between all molecules, due to the presence of moving
electrons ... but they are responsible for the phase issues of * nonpolar molecules
and are the weakest IMF. They are between all molecules but really associated with
nonpolar molecule.
Dipole Attractions are found between * dipoles (polar molecules)
Hydrogen Bonds are found between the molecules of a special category of dipoles and
are the strongest IMF
7) FactIMF: * Larger, more massive
because * larger molecules
molecules have stronger IMF than lighter molecules,
have more of the electrons that cause IMF
623
AN APPLICATION OF INTERMOLECLAR FORCES OF ATTRACTION
Vapor Pressure and Vapor Pressure Graphs
A) Vapor = The gas phase of a substance which is normally a solid or liquid at room temperature…
For our course we tend to use the terms vapor and gas phase interchangeably
1) Vapor Pressure = a measure of the force exerted by the gas phase above a liquid in a sealed
container.
2) Memorize: Wherever there is a substance as a *liquid, so too is there its gaseous phase
3) Gas molecules:
•exert a pressure when impacting the interior sides of their container
•are affected by changes in pressure and temperature
•have large potential energy and have large empty spaces between molecules
a) Pressure = (Mass)(Acceleration)
Area
4) Measuring Vapor Pressure
a) Initial Measurement
http://neon.chem.uidaho.edu/~honors/manom2.jpg
624
b) What happens when the liquid warms?
http://dbhs.wvusd.k12.ca.us/webdocs/GasLaw/VaporPressureImage.GIF
4) Evaporation : The phase change from liquid to gas from the SURFACE of a liquid.
a) evaporation occurs at all temperatures between the freezing point and the
boiling point of a liquid
b) * the rate of evaporation is temperature dependent
c) evaporation creates a vapor pressure
d) Wherever there is the liquid there is its gas !!!
Think about: a butane lighter
625
B) Vapor Pressure: The pressure exerted on a substance due to its gas phase
interp VP Graphs
normal boiling point
ID substances with strong
or weak intermolecular forces
1) Vapor = the gaseous phase of a liquid: Wherever there is a liquid, there too is its gas.
2) Liquids made with molecules that are held to each other with weak intermolecular forces of
attraction have high (large) vapor pressures and low boiling points
Picture It
http://wiki.chemeddl.org/images/f/f0/Chapter_10_page_13.jpg
The consequences of weak intermolecular
forces of attraction and vapor pressure
3) Liquids made with molecules that are held to each other with STRONG intermolecular forces
of attraction have relatively * lower
vapor pressures and * higher
normal boiling points
http://wiki.chemeddl.org/images/f/f0/Chapter_10_page_13.jpg
The consequences of strong intermolecular forces
of attraction and vapor pressure
626
4) Boiling Point: A temperature at which the vapor pressure = the prevailing atmospheric
pressure.
a) Boiling is a function of pressures and not of any specific temperature(s). (Gee! That's News!!)
b) Were you to adjust the pressure on a liquid, you could get it to “boil” at almost any
temperature.
5) NORMAL Boiling Point * The temperature at which the vapor pressure of the liquid is equal
to standard pressure (101.3 kPa or 1.0 atm)
6) The greater the atmospheric pressure, the more difficult it is to generate a vapor pressure high
enough to create a boiling situation.
http://www.chem.purdue.edu/gchelp/liquids/vpress.html
Temp Pressure
oC
atm
30
0.04161
32
0.04734
35
0.05528
40
0.07305
50
0.1214
60
0.1964
70
0.3079
80
0.4669
90
0.6920
100
1.000
Picture It
The same is true, for a low atmospheric pressure. The lower the atmospheric
pressure, the lesser the required energy to create a sufficient vapor pressure to
create a boiling (vaporization) situation. [water boils at a lower temperature]
http://www.chemcool.com/regents/physicalbehaviorofmatter/aim10.14.gif
627
VAPOR PRESSURE AS A FUNCTION OF TEMPERATURE (TABLE H)
IMF= an attraction between molecules
(they are weaker than bonds). They can
indicate how strongly one molecule is
attracted to another molecule
(acetone)
101.3 kPa
is standard
pressure
55 C is the normal boiling point for acetone because
it is the temperature at which the vapor pressure of
acetone = 101.3 kPa (standard pressure)
Remember, based upon the magnitude of the vapor pressure, you may infer a few things:
Assuming a low temperature:
 When the vapor pressure is a large number, then intermolecular forces of attraction
between the molecules must be weak and the normal boiling point is a low temperature.
Take Home Message: *large vapor pressure = weak IMF = low normal b.p.
 When the vapor pressure is a small number, then the molecules are clinging to each other
still, and you can infer the intermolecular forces of attraction are strong and the normal
boiling point is a relatively large temperature
Take Home Message: *small vapor pressure = strong IMF = higher normal b.p.
628
QUESTIONS:
1) Using Table H, of the NYS Reference Charts, record the vapor pressure for each substance at 50 C.
Your answers should be whole numbers.
Acetone’s at 50 C equals * approx 83 kPa
Water’s at 50C equals *approx 13
Ethanol’s at 50 C equals * approx 30
Ethanoic acid’s at 50C equals * approx 8 kPa
kPa
kPa
2) Based upon your answers to question 1, and your understanding of chemistry, which of the four liquids
of Table H, has the STRONGEST intermolecular forces of attraction between the molecules of the liquid?
(Think ... Strong IMF means that the molecules resist being separated from each other … what effect would a strong resistance to separating from each
other have on vapor pressure?)
* ethanoic acid
a) How do strong intermolecular forces of attraction between liquid molecules affect the rate of or ease
of a liquid’s evaporation?
___________________________________________________________________________
3) Based upon your answers to the first question and your understanding of chemistry, which of the four liquids
of Table H, has the weakest intermolecular forces of attraction between the molecules of the liquid?
(Think ... which one easily leaves the liquid phase and turns into a gas???)
* propanone (acetone)
a) How do weak intermolecular forces of attraction between liquid molecules affect the rate of or ease
of a liquid’s evaporation?
_____________________________________________________________________________
4) Differentiate between the terms: NORMAL boiling point of a liquid and boiling point of a liquid?
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
_________________________________________________________________________________
According to Table H, what is the normal boiling point for
a) acetone? * 55 C
(propanone)
b) ethanol? * 78 C
c) water?
__________C
d) ethanoic acid? * 118 C
5) In terms of IMF strength and the numeric values for the normal boiling point, answers to questions 2 -4
agree
with each other? _________ (did you pick the one with the highest normal boiling point, for instance?)
Suggest why your answers make sense.
629
XIII) Molecular Polarity: Due to similarities or dissimilarities in shape and/or partial charge across a molecule
molecules are divided further into two different categories.
Think: Different or
Uneven Shape/
Opposite Charge
distribution
Polar Molecules
(Dipoles)
Think: Same or
Even Shape / Lack
of Opposite Charge
distribution
Nonpolar Molecules
molecules with an asymmetry in shape
and/or the distribution of partial charge
symmetrical molecules in shape and/or partial charge.
-
(created by differences in electronegativity
values of the atoms of the molecule)
+
-
-
+
-
-
+
-
http://boomeria.org/chemtextbook/cch14.html
Dipoles tend to attract each other
and this intermolecular set of
attractions give substances very
special properties.
Nonpolar molecules tend to attract very weakly and these do not
dissolve well in dipoles (e.g. oil & water or egg yolk and egg whites)
soaps & detergents are molecules that are combinations
of nonpolar portions/molecule and polar portions/molecule
H H H H H H H H H H H H
| | | | | | | | |
| | |
HCCCCCCCCCCCCO-1 Na+1
| | | | | | | | | | | |
H H H H H H H H H H H H
nonpolar end of the molecule that dissolves into grease
polar end that dissolves into water
A) Molecular Polarity applies essentially to molecular substances (primarily existing due to covalent
bonding, including the organic compounds and the vast number of their derivative (such as soaps),
inorganic molecules, and diatomic elements
B ) As with covalent bonding ... Molecular polarity is something of a continuum. Molecules may be
“nonpolar” ... or slightly polar, moderately polar ... so polar it’s like, OMG (!)
We tend to deal with the extreme ends of this continuum, in our class.
630
A simplified piece on "resultant forces" of these shifting electron clouds….
H

Cl:

greater electronegativity
𝛿-
**************************************************************************
𝛿-
𝛿-


:O = C = O:
*********************************************************************
𝛿-
𝛿-
 
:O F:

:F:

631
Imagine 2 molecules of methane (CH4) as they approach each other... Note the partial positive charges on the
hydrogen atoms. What might happen as these two molecules approach each other?
H+
|
+ H ― C-― H+
|
H+
H+
|
+ H ― C-― H+
|
H+

Imagine a number of hydrogen chloride molecules, HCl or
http://intro.chem.okstate.edu/1515SP01/Lecture/Chapter12/Lec2201.html
H  Cl:


A) POLAR MOLECULES (a.k.a. * dipoles or dipole molecules
1)
polar = different
)
Essentially, you can recognize a dipole in 2 DIFFERENT ways:
a) when there is a distribution of opposite (but partial) charge across the molecule
This distribution of opposite charge is called * polarization
(better definition)
Polar Molecule: Look for molecules with:
b) OR the molecule has an uneven shape (asymmetrical) based on its Lewis
structure. (…pyramidal, bent and maybe linear)
opposite charge ± distribution
http://www.tutorsglobe.com/homework-help/organic-chemistry/intermolecular-forces-assignment-help-7502.aspx
uneven shape (bent, some
linear molecules & pyramidal)
O
//
carbonyl groups -C|
|
-C-O-H or –C-N-H groups
|
| |
H
(alcohols)
(amines)
632
2) Here's a little bit more for the Honors Student in you..... This is Purely Honors Chemistry
a) There is a concept called the dipole moment
 When there is a separation of opposite partial charge (δ) because of a difference
in electronegativity they give rise to an electric dipole moment.
You may wish to review your notes on electronegativity....
 A little physics is great here ... because essentially a dipole moment is a
* resultant force
Dipole moments are represented by an arrow pointing * towards the partial
negative charge.
 The unit of measurement for dipole moments is a Debye (D), which is defined so
that a single negative charge separated by 100 picometers (10-12) from a single
positive charge has a dipole moment of 4.80 D.
 A molecule with a dipole moment of 1.2 D would have 25% of an electron’s
charge on one atom with an equal positive charge on the other. (0.25 of 4.8 =1.2)
Dipole Moment of HBr
H is less electronegative than Br
2.1
H
2.8
Br
A dipole moment of 1.38 D in
the direction of the more electronegative Br
http://www.chem.ufl.edu/~itl/2045/lectures/lec_16.html
b) Effectively, you can recognize a dipole when you assign partial charges based upon
electronegativity values. Dipoles molecules have at least one axis with opposite partial
charge separation.
633
B) NONPOLAR MOLECULE: Any molecule which LACKS a distribution of opposite charge
at any either applicable axis of the molecule. (The ends of the molecule look the same ...
thus drawing the molecular shape becomes an important skill)
OR nonpolar molecule = any molecule which is symmetrical in shape (hence the
charge distribution will be identical [no difference or SAME] by default)
Tuck this little fact away ... Hydrocarbons (alkanes, enes, ynes, arenes) are considered
to be nonpolar molecules ... (but be careful(!) When you add O, N, halogens... you don’t
have hydrocarbons any longer....and molecular polarity could change....)
C) Now, in reality, water (a polar molecule), can to some level, dissolve the vast majority of molecules.
However, the level might be at a range below ten thousandths of a gram …. and thus water is not
considered a reasonable solvent for such compounds.
1) Given this there is however, another continuum idea, that can generalize, issues of solubility,
for molecules. This is the idea of “like dissolves like”. Now, remember, this is just a general
trend and represents a continuum of molecular water solvent interaction with molecular
solutes.
D) Applications of molecular polarity: Stain removal, super-oxygenated fluids, energy extraction etc...
Each is based upon an important application called:
1) LIKE DISSOLVES LIKE * Polar substances dissolve in other polar substances and
nonpolar substances dissolve in other nonpolar substances.
e.g.) Stop with the turpentine on your skin ... Go for the olive oil!!!
MATTER / MIXUTRES
MADE WITH POLAR
MOLECULES
MATTER / MIXTURES
MADE WITH NONPOLAR
MOLECULES
WATER
OIL / GREASE / FAT
* Alcohol (C-OH),
* methane, propane, butane,
Ethanol, Methanol, Glycols
hexane ...
* Ammonia
* dioxygen
* carbon dioxide
* carbon tetrachloride
* kerosene
634
Using: Like Dissolves Like ... Other applications
3) Okay Ya gotta go out and get the movie The Abyss. It is a typical boy meets girl, boy
loses girl, boy joins a deep ocean expedition, where he meets up with girl... Mayhem
ensues and it's all about realizing one's heart's desire ....
It's crap .... but it's really cool crap ...because it is going to introduce you to a real material,
broadly classified as a perfluorocarbon (purr-flur-oh-car-bon).
It is used to enable seriously deep water work, at depths where the pressure would crush the
lungs of the diver. The diver breaths in a nonpolar perfluorocarbon, saturated with dioxygen
gas ... and this is taken right into the lungs ...
see: http://johnclarkeonline.com/2011/06/20/liquid-breathing-its-not-as-easy-as-it-looks/
See, the nonpolar (but very liquid) perfluorocarbon can dissolved nonpolar dioxygen!
Like dissolves Like, yeah baby....
A classic perfluorocarbon is:
You can guess that it began
a hydrocarbon, but all of the
hydrogen have been
substituted with fluorine.
http://www.medicinescomplete.com/mc/martindale/current/images/c307-34-6.gif
With this... we are beginning to produce "synthetic bloods" that will afford surgical patients
a less stressful surgery .... check out: http://tinyurl.com/3fagf8w
or http://biomed.brown.edu/Courses/BI108/BI108_2005_Groups/10/webpages/PFClink.htm
Further (very cool) research reading can be found at: http://tinyurl.com/3ccqm3l
or
https://bdigital.ufp.pt/dspace/bitstream/10284/368/1/perfluorocarbons.pdf
Oh yeah, check out the picture:
This mouse is fully submerged in a sample of
perfluorocarbon fluid, saturated with dioxygen gas.
The mouse inhales the fluid mixture, and can
"breath" by exchanging nonpolar carbon dioxide
of it lungs with the dioxygen of the
perfluorocarbon
http://www.cracked.com/article_17476_7-man-made-substances-that-laugh-in-face-physics.htm
Know It:
Like Dissolves Like....
635
Using: Like Dissolves Like ... ONE MORE TIME!!!!
2) Hey Global Thinkers!
...
From NGEO "Dawn of the Ocean" 2 Sept 2010
....
Scientists at the University of Kiel, plan to take nonpolar CO2(g) molecules from the atmosphere and
pump them into areas of the sea bed that contain nonpolar methane hydrate stores (CH4) (also called
methane clathrates). Methane molecules become trapped in the frozen cages of water-ice (recall, as
http://www.noc.soton.ac.uk/gg/IPY/background.html
water expands as it freezes.) This occurs as low temperature and fairly
high pressure ...There are significant deep oceanic deposits in the Gas
Hydrate Stability Zone (GHSZ)
Anyway, by pumping CO2 into the area of clathrate formation, in theory the
nonpolar carbon dioxide molecules will dissolve the nonpolar methane, and
replace the methane molecules.
The methane will be pumped up and out, condensed and shipped for use as the fossil fuel that it is ....
Thus, the scientists are trying to integrate issues surrounding global warming with the greater extraction
and use of fossil fuels . Any thoughts? What must be considered? Would you buy stock in a company?
Reading further: Go To: https://www.llnl.gov/str/Durham.html
http://marine.usgs.gov/fact-sheets/gas-hydrates/title.html
Picture:
http://www.noc.soton.ac.uk/gg/IPY/background.html
In terms of concentration one liter of methane clathrate solid would contain, on average, 168
liters of methane gas at STP.
Calculation: The average methane clathrate hydrate composition is 1 mole of methane for every 5.75 moles of water. The
observed density is around 0.9 g/cm3. For one mole of methane, which has a molar mass of about 16.04 g, we have 5.75 moles
of water, with a molar mass of about 18.02 g, so together for each mole of methane the clathrate complex has a mass of 16.04 g
+ 5.75 × 18.02 g = 119.65 g. The percent composition of methane, therefore, is equal to 16.04 g / 119.65 g = 0.134.
The density is around 0.9 g/cm3, so one liter of methane clathrate has a mass of around 0.9 kg, and the mass of the methane
contained therein is then about 0.134 × 0.9 kg = 0.1206 kg. At a density as a gas of 0.717 kg/m3 at 0 °C, that means a volume
of 0.1206 / 0.717 m3 = 0.168 m3 = 168 L. http://en.wikipedia.org/wiki/Methane_clathrate#cite_note-5
.... And that's not all... Some folks have hypothesized that the disappearances of ships and planes in the
Bermuda Triangle, may be due to the destabilization of methane hydrates ...releasing huge amounts of methane
gas, that lower the density of water so much (ships sink), and of air so much (planes can't stay aloft), that they
are sent to the bottom of the sea....
http://www.bermuda-triangle.org/html/methane_hydrates.html
636
D) Complete:
Substance
Lewis Diagrams
Type of Molecule
(PM or NPM)
Type of Bonds
(PCB or NPCB)
*NPM
*PCB
*PM
*PCB
Dipole Moment
Drawing
CCl4
H2S
..
:S - H
|
H
HF
NI3
Br2
PH3
CH4
Thought Questions: Do water and oil mix to produce a homogeneous mixture?
Should molecules of an oil be attracted to water molecules?
(These are really 2 different questions… Think hard ... Math or Theory??)
Here’s an example of a monounsaturated
oil molecule found in the mixture,we call
olive oil http://www.cardiactherapy.org/ChewingTheFat.htm
* The molecules of oil and water don't mix homogeneously .... but they do attract each other.... The + of all
those hydrogen atoms would be attracted to the - of water’s oxygen atoms …and look at the OH group at the
end…. (hence the oil spreads out over the surface)… but the hydrogen bonding between the water molecules is
just so much stronger than the oil/water attraction, that the oil molecules can’t “break in” and become
surrounded by water. … (think of water like a really strong clique … think of the movie “Mean Girls”). This
is why detergents (DAWN) help to mix oil and water … The DAWN surfactants weaken the IMF attraction
between the surface molecules of water .... As a side note, individualized molecules of oil, may and can
dissolve into water …but they must be highly individualized.
637
As with bonds, and molecular polarity, the concept of an Intermolecular Force is a continuum, running from
the rather weakly interacting forces to the pretty darn strong interactions of forces known as hydrogen bonds.
The take home message is that these forces due to un-balanced and/or opposite partial charges are exerted
(exist) between molecules and affect issues such as:
the phase of matter (s, l, g)at a specific temperature and pressure
the melting point,
the boiling point
density,
and
molecular solubility in water (….or in alcohol, acetone, oil mixtures…)
XIV) IMF .... (often called molecular forces of attraction or van der Waals forces)
A) Intermolecular forces are forces of attraction or repulsion which act between neighboring
molecules
They are weak compared to intRAmolecular forces (the bonds), which keep a molecule together. For
instance, the covalent bond present within HCl molecules is much stronger than the forces present
between the neighboring molecules, which exist when molecules are sufficiently close to each other.
As written, some IMF are really weak … and others are much stronger….hence, a continuum. None
of the IMFs are as strong as a bond, but these forces do create “crowds of molecules” (a metaphor for
multiple molecules in phase) and these “crowds” or phases have pretty special characteristics.
Visualize
weakest
London Dispersion Forces
very weak, but have a cumulative
effect with increases in mass
strongest (about 5% of a covalent bond)
Dipole Attractions
due to more permanent
  charges housed on
molecules
Hydrogen Bonds
strongest IMF … due to larger  
charges. Sometimes described as “superdipole” forces … because the strength of
these IMF affect the very stuff of … LIFE!
B) One Consequence (One Take Home Message): Some molecular compounds have higher melting
points when compared to other molecular compounds, because of the strength (or weakness) of their
intermolecular forces of attraction.
638
C) 3 Types of Intermolecular Forces of Attraction
(a.k.a. van der Waals forces)
1) London Dispersion Forces : Found between all molecules – but associated with nonpolar
molecules most closely.
a) LDF come from the distortion of the e- cloud due to a temporary and unequal
distibution of e- around the nuclei. Small areas of  on different atoms, attract each other.
i) a weak IMF due to instantaneous polarizations, due to the “correlated movements
of the electrons of different molecules. Electrons of the different molecules start
repelling each other and the electron clouds are pushed and pulled around, creating
imbalances in the electron cloud densities of the interacting molecules.
b) It is VERY IMPORTANT to note that: The magnitude of self-polarization increases
with increasing numbers of electrons (and therefore mass)
Open to activate: http://www.wou.edu/las/physci/ch334/lecture/intermol/london.htm
c) Hydrocarbons, diatomic elements and (oddly enough) linear molecules like CO2 are
exellent examples of NONPOLAR molecules with issues of phase, melting point... etc,
explained by the weakness (or strength) of the London Dispersion Forces BETWEEN their
molecules
Take Home Message: When it comes to nonpolar molecules and the strength of the IMF
between those molecules, * the size and mass of the molecule matters.
Heavier molecules imply a greater number of electrons (due to more protons ...) and thus the
opportunity and degree of the induced (but temporary) polarization can be greater.
e.g.) While samples of F2(g) and I2(s) represent nonpolar molecules ... the London Dispersion
Forces are of different strengths ... F-F to F-F interactions are weaker than I – I to I – I
interactions, because of iodine’s greater number of electrons (and greater number of
probable polarizations ... hence samples of di-iodine are solid at STP while difluorine is a gas.
639
Practice:
a) The diagrams represent nonpolar molecules. The intermolecular forces of attraction are strongest
between which set of molecules?
a)
b)
c)
d)
Now, Explain WHY by completing the following paragraph.
(When given choices, separated with a / ... circle the most correct
choice to make the statement accurate, in terms of the theory) Fill in most blanks with words such as: greatest/least, largest/smallest
circle one
Explanation: All of the molecules in every choice are: dipoles / nonpolar. Thus the primary intermolecular
circle one
force of attraction is Hydrogen Bonds / LDF.
circle one
These are the strongest / weakest of the forces. These forces
circle one
circle one
increase / decrease in strength as the mass of the molecule increases due to a greater / lesser number of
circle one
circle one
electrons. This greater / lesser number of electrons creates a greater / lesser chance for cloud distortions
and self-polarization.
Since, choice *d
shows molecules * greatest
the force of attraction between these molecules will have the * greatest
distortions and thus experience a *
in mass, then
number of cloud
stronger intermolecular attraction, affecting, density, boiling point ....
b) EACH of the following formulae represents a NONPOLAR gas. The only
intermolecular force of attraction between non-polar molecules is the very weak (London)
Dispersion Forces.
Assume 1 mol of each gaseous compound. Based upon mass circle the chemical in each pair
that should exert the greater (London) dispersion forces on like molecules
CO2(g) vs.
O2(g)
Which probably has the greater melting point / boiling point?
due to stronger London Dispersion Forces?
640
CH4(g) vs.
c)
C4H10(g)
Which probably has the greater melting point/boiling point?
C5H12(l) vs. C8H18(l)
Which probably has the greater melting point/boiling point?
The hydrocarbon 2-methylpropane reacts with iodine as represented by the balanced equation
below. At standard pressure, the boiling point of 2-methylpropane is lower than the boiling point of
2-iodo-2-methylpropane.
(An Idea... Keep It Simple Students [K.I.S.S.]
Is this a math question or a theory question??? )
Explain the difference in the boiling points of 2-methylpropane and 2-iodo-2-methylpropane in
terms of both differences in molecular polarity and differences in intermolecular forces.
* This is with what the Regents allowed you to get away.... Allow a maximum of 2 credits, allocated as follows:
• Allow 1 credit for correctly describing the molecular polarities.
Acceptable responses include, but are not limited to:
The molecules of 2-iodo-2-methylpropane are more polar than the molecules of 2-methylpropane.
• Allow 1 credit for correctly describing the intermolecular forces. Acceptable responses include, but are not limited to:
There are stronger intermolecular forces between molecules of 2-iodo-2-methylpropane.
*However, my students should
answer (e.g. on an exam):
2 methylpropane is a hydrocarbon and virtually a
nonpolar molecule, thus only LDF would exist between
nonpolar molecules.
However, due to the addition of the Iodine,
the 2-iodo-2-methylpropane is slightly polar
(and has significantly more e-) thus the LDF
experienced would be greater and there
would probably be a slight distribution of opposite
charge, creating partial charges that could be
attractive with other molecules …thus increasing
the boiling point.
641
XV) C) IMF (continued)
2) Dipole Attractions: In addition to LDF, a second (& stronger) IMF is found between most
* polar molecules
These are due to a permanent (yet still incomplete) distribution
of opposite and partial charge, predicated upon electronegativity values.

a) symbol: partial charge =
b) Dipole attractions are often denoted by a dashed (----) line between (inter-) molecules. The
negative region of one molecule, attracts the * positive
region of * a different molecule
Here’s a neat application:
c) The compounds, bromine and iodine chloride are very similar in molecular mass (160  vs. 162 )
However, the normal boiling points of the two substances are significantly different. Using
the current understanding of IMF explain the iodine chloride’s higher boiling point
Bromine
Iodine chloride
(Br2) or
Br-Br
(ICl) or
I-Cl
Normal Boiling Point (C)
59
Molecular Mass ()
160
97
162
Based on boiling point, which substance has the stronger IMF?
One substance is a polar molecule. Which is it?
*ICl
*ICl
One substance is a nonpolar molecule. Which one? *Br2
Explain why there is a difference in normal boiling points. * The masses are so close, that LDF probably do
not matter. But, one molecule is a dipole, and thus creating a more permanent, stronger partial, but opposite
charge distribution. This creates a dipole force increasing the strength of the attractive force between the
molecules, increasing the amount of energy required to vaporize (boil) the substance.
642
3) Hydrogen Bonds: Some polar compounds exhibit an extreme form of dipole attractions
between like molecules, called hydrogen bonding (or hydrogen bonds).
a) In this course, I consider the name, hydrogen bond to be unfortunate.
Despite its name, hydrogen bonding is a form of Intermolecular Force of Attraction
b) Molecules exhibiting hydrogen bonds are "super-dipoles". Hydrogen bonds are stronger than
* "regualr" dipole attractions
,
but not as strong as a "full"
* covalent bond (only about 5% as strong)
c) Hydrogen bonds are formed BETWEEN molecules when one molecule has
H bonded to * F, O, N
and a second molecule that has atoms of * F, O, N
How can DNA molecules "unzip" rather readily at replication....
************************************************************************************************************************
Why the volume of a mass of ice is greater than the volume of an equal mass of liquid water....
643
d) Why are H-Bonds such strong IMF? Effectively, an atom of H is bonded to special
central atoms.
i) the central atom has a small atomic radii
(like the nonmetals to the extreme right of the PT)
ii) high electronegativity values especially as in the atoms of F, O, N
Both factors help to create a super-large partial charge distributed across the molecules.
Think about peanut butter a slice of bread and a Peppridge Farms Goldfish cracker
http://www.pfsda.com/history/90/
http://www.tastespotting.com/features/national-peanut-butter-day
e) Effects of Hydrogen Bonding: unusually high b.p., low vapor pressure, fairly large specific
heat constants
Boiling Points of Group 16 Hydrides
http://witcombe.sbc.edu/water/images/bptable.gif
644
Normal Boiling Points and the Effects of Hydrogen Bonding
SUBSTANCE
H2O compare
H2S compare
BOILING POINT (˚C)
NH3  compare
PH3  compare
+100



88
HF  compare
HCl  compare


Effect on IMF between molecules with
H bonded to F



Study the normal boiling point of three
molecules that do NOT have H-bonds
between molecules
Effect on IMF between molecules with
H bonded to O and other like molecules
Effect on IMF between molecules with
H bonded to N

CH4
O2
H2
APPLICATION:
Challenge: Which of the following substances is most likely to exist as a gas at room temperature and
a pressure of 1 atm: C2H5OH, Cl2, AgCl, or I2 ? Why?
Think:
Is this a math question or a theory question?
if yes:
if yes
Identify equation(s) or procedure(s)
Identify the concept/theory by name
What values do you know?
What values are unknown?
Input values into an equation
and begin your solution.
Write the tenet(s) of the basic concept.
Explain how the question &/or
your answer, meets the tenent(s)
Here's a solution: * In essence, the question asks which substance has the weakest IMF.
The weaker the (total) forces, the more likely the substance exists as a gas ... With that written, the following thought
process may help.
Toss out AgCl. It is ionic and all ionic compounds are solids at the above conditions, due to the strength of the bonding
electrostatic forces applied to surrounding ions of the crystal.
C2H5OH is a dipole and will exhibit hydrogen bonding between molecules (due to the OH) as well as LDF (because LDF are
present between all molecules...due to the presence of electrons)
We now come down to the nonpolar molecules of Cl2 and I2. Larger molecules have stronger IMF, hence a sample of I2
exerts stronger IMF than the Cl2 molecules or rather, the molecules of Cl2 are less likely to attract each other strongly, thus
a sample of chlorine gas molecules is most likely to exist as a gas at room temperature (21ºC to 23ºC) & 1 atm.
645
4) Molecule - Ion Attractions: found only in (aq) solutions: accounts for the attractions between
* water molecules (polar)
and an * ionic solutes
This attraction creates * hydrated ions
.
(electrolytes: ions surrounded by water molecules)
a) due to * water molecules’
attraction for the * ions
added to it.
http://cyberbridge.mcb.harvard.edu/images/bonding2_3.png
Study the diagram of NaCl in Water. What is going on between the
molecules of water, relative to the ions? Be specific in your analysis.
_
Alternate Image

+

+
Cl1-
Na1+
+


+
+
_
+
_
+

+
646
Now, at this "point", your teacher would like make a technical "point" , so here we are again, at
something which is : Purely Honors Chemistry
First, let's summarize the IMF:
IMF
General Application
Found between all molecules because the
London
force is generated by the effects of the
Dispersion variable movement of electrons ...and all
molecules have electrons
Comment
Seen, generally as the only IMF
between nonpolar molecules.
LDF are generally viewed as the
weakest IMF...but cummulative
Found between most dipoles due to the
Dipole
permanent partial charges which are
Attractions evolved due to differences in
electronegativity values of bonded atoms.
Hydrogen
Bonds
A form of dipole attraction. This is an
unusually strong IMF, Classically
described as existing between a molecule
which has H bonded to F, O, N and a
second molecule with atoms of F, O, N
(the presence of H is optional).
Not really an IMF, since it is a force of
Moleculeattraction between water molecules and
Ion
dissolved ions ... as in aqueous solutions
Attractions
of ionic compounds.
The small radius and large
electronegativity of F,O,N establish
relatively large and permanent partial
charges. A hydrogen bond is only
about 5 % of the strength of a
covalent bond
This attractive force helps to explain
the solubility of ionic compounds in
water, and the concepts of electrolytes
in water (a.k.a. hydrated ions)
Generally, speaking the stronger the total IMF, the greater the melting point and the greater the normal
boiling point of the molecular material.
Translation: The stronger the attraction between molecules, the more energy it takes to
sufficiently move them away from each other, in order to effect a change in phase.... once
achieved, the phase change will continue at a constant temperature.
647
Now, with all of that said ... what would be your response were I to say: The total effect of LDF between
molecules, can result in an overall higher normal boiling point than the total effects due to Hydrogen
Bonding alone? Could that make sense??
* Consider these data:
Olive Oil
Approximate
Boiling Point (ºC)
253
Soybean Oil
254
Water
100
Material
Density (g/mL)
Composition
0.914 to 0.918
Palmitic Acid (C16H32O2)
and various
Octadecanoic acids
(C18H36O2)
depending upon composition of the mixture
0.924-0.927
depending upon composition of the mixture
1.00
at 4ºC
hydrogen and oxygen atoms
*How can we account for the greater boiling points in the above (nonpolar) oils versus the water, which
has the super-dipole force of attraction between its molecules? (Hint: begin by considering the origin of hydrogen bonds vs.
the origin of LDF)
*Why does the hot cooking oil spatter and crackle when I but foods into it ... but the oil does NOT spatter
when I add oils to hot water? (JCE: Nov 2009 p 1281-85)
648
MOLECULES AND IMF
(all comparisons assume
similar pressure and temperature)
help to explain physical properties
like solubility, boiling point,
density and melting point
2 Ways we can categorize Molecules
x
related to each other
x
3 Types of IMF
 Dipole
Attractions
found between dipoles
 even/same/
no difference in
distribution of
partial charge
x
x
stronger than LDF because
the electron cloud
distortion or
polarization is more
permanent
x
x
x
x
Molecule-Ion Attractions
not really a true IMF ... but close
enough...
accounts for hydrated ions
attraction between ions and
water molecules
649
Create a concept map using the following terms / descriptions.
Nonpolar
Molecule
s
 uneven / difference in the
distribution of partial charge
 uneven / different shape
(pyramidal, bent, some linear)
 even/same/
no difference
in shape
Polar
Molecules
(Dipoles)
Bonding tends to be independent of the type of
molecule. Nonpolar molecules may have polar
covalent bonds or nonpolar covalent bonds.
 Hydrogen Bonding
misnamed (not a bond...)
a special type of dipole attraction
(a "super-dipole attraction)
found between a dipole made
with H-F,O,N and another
dipole with F, O, N.
London Dispersion
Forces
found between all molecules
due to temporary distortions
in the electron cloud
become stronger as the size of
the molecule increases.
Heavier molecules have
stronger LDF.
The primary IMF accounting
for the physical properites of
NONpolar molecules
650
And think about this flowchart as you answer questions:
INTERACTING MOLECULES OR IONS
yes
Are the ions
in water?
yes
Then this is
all about
molecule-ion
attraction
Are polar molecules (dipoles)
involved?
Are nonpolar molecules
involved?
Are ions involved?
yes
Is it about a
solid ionic
compound?
yes
Then any
physical
property
(e.g.)
melting
point, is
due to the
nature of
& the
strength
of the
ionic bond
itself
yes
Is the question about
physical properties or
bond types
if physical properties
if bond types
Then think LDF
which are affected
by shape (long &
skinny vs. chunky)
& greater mass
Then
analyze
the
molecule
… in all
likelihood,
at our
level, the
bonding is
nonpolar
covalent.
Is the question about
physical properties or
bond types
if physical properties
is H-F,O,N involved?
Hydrogen bonds or
hydrogen bonding
is H-F,O,N absent?
just dipole attractions
if bond types
Then
analyze
the
molecule
the
bonding is
polar
covalent.
651
Here are 2 applications of IMF for "real life" !!!!
Gecko's amazing sticky feet
BBC News Online: Sci/Tech http://news.bbc.co.uk/2/low/science/nature/781611.stm
Wednesday, 7 June, 2000, 18:17 GMT 19:17 UK
The mystery of how geckos manage to scurry up walls and stick to
ceilings may have been solved by scientists. It seems the little
lizards have a network of tiny hairs and pads on their feet which
produce electrical attractions that literally glue the animals down.
With millions of the hairs on each foot, the combined attraction of
the weak electrical forces allow the gecko to stick to virtually any
surface - even polished glass.
Californian researchers believe the reptile's sticky toes could now
help them to develop a novel synthetic adhesive that is both dry and self-cleaning.
If a human hand had the equivalent "sticking power", it could lift huge weights. "If the hands were maximally attached,
we estimate that kind of size would be able to hold about 90 pounds (40 kilos) or so," Professor Autumn Kellar, one of the
researchers in the gecko study, told the BBC.
Noisy creatures
Geckos are small, insect-eating, and often very noisy creatures that have become popular pets.
Biologists have long admired the animals' ability to walk up smooth surfaces but have never
really understood how it was done.
Suction was regarded as an unlikely explanation since geckos can cling on to a wall even in a
vacuum. That astonishing trick of walking upside down on the ceiling would seem to rule out
friction.
Furthermore, without any glands on their feet, it would be hard for geckos to produce their
own natural glue.
But a team of researchers, led by Professor Robert Full, now think it may all come down to
van der Waals forces - the weak attraction that molecules have for one another when they are brought very, very close
together.
Outstanding adhesives
The scientists looked closely at the feet of a Tokay gecko (Gekko gecko) which is native to South-East Asia. Close-up
pictures reveal about two million densely packed, fine hairs, or "setae", on each toe.
The end of each seta is further subdivided into hundreds to thousands of structures called spatulae.
Professor Full's team of biologists and engineers calculated the combined adhesive force of all the tiny hairs lining the
gecko's toes is 10 times greater than the maximum force reportedly needed to pull a live gecko off the wall.
"These billion spatulae, which look like broccoli on the tips of the hairs, are
outstanding adhesives," said Professor Full, head of the Poly-PEDAL (Performance,
Energetics, Dynamics, Animal Locomotion) Laboratory at the University of
California, Berkeley.
He said: "Geckos have developed an amazing way of walking that rolls these hairs
onto the surface, and then peels them off again, just like tape. But it's better than tape."
Professor Full's team believe the stickiness of the gecko can now be attributed to intermolecular forces so weak
they are normally swamped by the many stronger forces in nature.
652
Unbalanced charges
These forces come into play, though, because the gecko foot hairs get so close to the surface.
He said: "The hairs allow the billion spatulae to come into intimate contact with the surface, combining to create a strong
adhesive force.
"Our calculations show that van der Waals forces could explain the adhesion, though we
can't rule out water adsorption or some other types of water interaction."
Van der Waals forces arise when unbalanced electrical charges around molecules attract
one another.
They are responsible for the attraction between layers of graphite, for example, and the
attraction between enzymes and their substrate.
Though the charges are always fluctuating and even reversing direction, the net effect is
to draw two molecules together, such as molecules in a gecko foot and molecules in a
smooth wall.
In yet-to-be published work the gecko hairs have been shown to be self-cleaning, unlike any other known adhesive. Work
has also begun on building a mechanical gecko that Professor Full hopes will lead researchers to a new, synthetic, dry
adhesive.
The gecko research is published in Nature.
SEM images by Kellar Autumn & Ed Florance
653
Previous Story / Next Story / Volume 20 archive
Phys. Rev. Lett. 99, 198103
(issue of 9 November 2007)
Title and Authors
2 November 2007
Clarity through Diversity
N. Dorsaz & G. Foffi/EPFL & IRRMA
Goldilocks effect. Two different-sized eye-lens
proteins, modeled as spheres in this simulation,
segregate if their mutual attraction is too small
(top) and clump if it is too large (bottom), but
they stay mixed if the attraction is just right
(center).
Milky-white cataracts, the world's leading cause of
blindness, can occur when proteins in the lens of
the eye aggregate into clumps. In an upcoming
issue of Physical Review Letters, researchers report
that although one pure lens protein forms clumps, a
mixture of that same protein with another lens
protein is less clumpy. By comparing experiments
with extensive computer simulations, they conclude
that the effect arises because the two proteins attract
each other, but not too strongly. The new information
on lens protein interactions could have benefits
beyond cataract research because controlling similar
attractions could help keep particles dispersed in
material and food processing.
The lens of the eye consists of an ordered array of
cells, filled mostly with water and several proteins
called crystallins. The lens is clear only when the
different protein types are evenly dispersed. But if
they clump up or segregate from one another by
type, a cataract can result because the clumps
scatter light, somewhat like the droplets of
condensed water that make up clouds.
For decades, researchers have studied the
segregation and aggregation properties of naturally
occurring mixtures of lens crystallins and of single
components, but no one has looked at just two
crystallins at the high concentrations that occur in
the eye. A Swiss and American collaboration led by
Peter Schurtenberger of the University of Fribourg
in Switzerland has now explored the behavior of
two of the main crystallins, using neutron scattering
to probe their detailed structure. First the team
looked at each protein on its own. They confirmed previous findings that the larger of the two
654
acts just like a collection of 18-nanometer-diameter billiard balls, but the smaller molecules, only
3 or 4 nanometers in diameter, tend to stick together, forming light-scattering clumps. But when
the researchers mixed the two, the clumping was reduced.
To investigate why the larger crystallin reduced clumping of the smaller one, the team performed
large-scale simulations using a group of networked computers. Guided by the known singlemolecule behavior, they used tens of thousands of hard spheres to represent the protein
molecules. They mixed spheres with two different diameters and made the smaller ones sticky.
The team then varied the attraction between the large and small proteins. With no attraction, an
initially uniform mixture separated into regions that were rich in either large or small proteins, in
disagreement with the original lab experiment.
But adding a small attraction between the large and small proteins kept the two species
thoroughly mixed. Moreover, the detailed structure in the simulation agreed with that observed by
neutron scattering. "We can overcome [the segregation] by turning on a little bit of an attraction
between the small and the big ones," says Schurtenberger. But if the researchers made the simulated
attraction even a little stronger, both small and large proteins started to bind together in large
clusters. "The stability that we find comes from a finely-tuned balance," he says, suggesting that a
similar balance may be needed for healthy lenses.
In the long run, researchers hope that modifying the protein interactions could prevent cataracts.
But Schurtenberger also notes that tuning intermolecular attractions could help maintain
uniformity in food processing and in advanced materials used to make optical fibers.
Annette Tardieu of the University of Paris 6 and the National Center for Scientific Research
(CNRS) in France says that such a crystallin mixture "has never been studied before in detail" and
may well give insight into cataracts. But she is not convinced of the role of the attractive force,
because the hard spheres used in the simulations could mask other important details of real
proteins. "I would prefer to trust the experiments," she says.
--Don Monroe
Don Monroe is a freelance science writer in Murray Hill, New Jersey.
New Insight Into Cataract Formation: Enhanced Stability Through
Mutual Attraction
A. Stradner, G. Foffi, N. Dorsaz, G. Thurston, and P. Schurtenberger
Phys. Rev. Lett. 99, 198103
(issue of 9 November 2007)
Previous Story / Next Story / Volume 20 archive
ISSN 1539-0748 © 2008 by The American Physical Society. All Rights Reserved.
655
NAME________________________________________
IMF PRACTICE
Directions: For questions 1-8, use the following choices:
1)
2)
3)
4)
London Dispersion Forces...(between nonpolar molecules)
Dipole Attractions...(between most dipoles)
Hydrogen Bonding...(a super-dipole attraction between molecules with ... H-FON and other’s with FON)
Molecule-Ion Attractions...(not really an IMF, but found with hydrated ions (ionic compounds in water))
_____1. Which of the following is most responsible for the low normal boiling point of CH4(g) ?
i) THINK: Is this molecule polar or nonpolar?
_____2) Which of the above is responsible for the high normal boiling point of NH3(g)?
i) THINK: Is this molecule polar or nonpolar?
_____3) Which of these is found between molecules of I2(s)?
i) THINK: Is this molecule polar or nonpolar?
_____4) The forces of attractions which exist between molecules of H2S are _________
i) THINK: Is this molecule polar or nonpolar?
_____5) Study Group 17 which of these best explains why F2 is a gas at STP, but I2 is a solid at STP ?
i) THINK: Are these molecules polar or nonpolar?
_____6) Which are responsible for the low boiling point of CO2(l)  CO2(g) ?
_____7) What are responsible for the unusually high normal boiling point of water H2O(l)?
_____8) What forces of attraction exist in a 100 mL sample of KCl(aq)?
For questions 9 - 16 select/provide the most correct answer from the choices provided.
_____9) Intermolecular forces of attraction are STRONGEST between the molecules in a sample of
1) H2O(g)
2) H2(s)
3) H2O(l)
4) H2O(s)
c) KBr(aq)
4) CCl4(l)
_____10) Molecule-ion attractions are found in
a) Cu(s)
b) CO(g)
_____11) The reason why H2O has such an unusually high boiling point is due to
1) ionic bonds
2) hydrogen bonds
3) metallic bonds
4) coordinate covalent bonds
656
_____12) Citing the qualities of __________ helps to explain why nonpolar CH4 is a gas at STP while
nonpolar octane (C8H18) is a liquid at STP
1) polar covalent bonds
2) dipole attractions
3) London Dispersion Forces
4) ionic bonds
_____13) Using the idea of "like dissolves like", NH3(g) is most soluble in a sample of
1) CCl4(l)
2) H2O(l)
3) N2(l)
4) CO2(l)
14) Neither oxygen gas nor carbon dioxide gas are very soluble in water. Why ? ______________
_______________________________________________________________________________
15) Water can NOT get out a stain made from mayonnaise (which is mostly oil), but CCl4 can remove
the stain. Why?
_________________________________________________________________________________
16) Ascorbic acid (Vitamin C) has the following structural formula:
H
|
H-C-OH
|
HO-C-H
|
O
H-C
|
C
|
OH
Scurvy, a deficiency in Vitamin C, was one of the earlier nutrient-deficiency
diseases to be recognized. It was the bane of extended voyage seafarers. They
suffered from vomiting, bleeding gums, anemia and slow healing wounds. In
1735 Dr. James Lind showed that scurvy could be prevented by the inclusion of
fresh citrus fruits in the diet. The British Admiralty required all ships to carry a
C==O supply of limes. (thus the colloquial name of “limeys” given to British sailors).
|
The determinative factor in citrus fruits was/is vitamin C. Vitamin C must be
C
taken “fresh” because the vitamin is destroyed by cooking.
|
OH
a) Based upon its structural formula, is Vitamin C a dipole or a nonpolar molecule? _____________________
b) Based upon its composition and structure what type of IMF would you predict exists between water molecules and
ascorbic acid ?
Answer : ________________________________ Defense _____________________________________
______________________________________________________________________________________
c) Based upon its structure and the information, would you expect Vitamin C to be eliminated from the body in
water-based urine or stored in body fat? What implications might your answer have with respect to your
requirement for daily Vitamin C?
Answer: ________________________________________________________________________________
________________________________________________________________________________________
________________________________________________________________________________________
657
___17) Which compound has hydrogen bonding between its molecules?
1) CH4
2) CaH2
3) KH
4) NH3
___18) As a liquid sits in a beaker, it evaporates into the gas phase. That gas phase exerts a pressure on the
liquid. That gas phase is called the vapor pressure.
The weaker the IMF between molecules in the liquid phase the more readily the molecules move into
the
gas phase and hence have a greater vapor pressure.
Using your knowledge of chemistry and the information of Table H, which statement concerning
propanone and water at 50ºC is true?
1) Propanone has a higher vapor pressure and stronger intermolecular forces than water
2) Propanone has a higher vapor pressure and weaker intermolecular forces than water
3) Propanone has a lower vapor pressure and stronger intermolecular forces than water
4) Propanone has a lower vapor pressure and weaker intermolecular forces than water
___19) Which type of molecular attraction accounts for the unusually high boiling point of H2O?
1) molecule-ion
2) dipole attractions
3) london dispersion
4) hydrogen bonding
___20) Which Group 16 element when combined with hydrogen forms a compound that would exhibit
the strongest hydrogen bonding?
1) selenium
2) tellurium
___21) When compared to H2S,
1) metallic bonds
3) oxygen
4) sulfur
H2O has a higher boiling point because H2O contains stronger
2) covalent bonds
3) ionic bonds
4) hydrogen bonds
___22) Which characteristic of the compound C5H12 causes it to have a higher normal boiling point than C2H6?
1) The distance between molecules of C5H12 is greater
2) The force of attraction between molecules of C5H12 is greater
3) C5H12 has a greater number of ionic bonds
4) C5H12 is a smaller molecule
658
___23) Which structural formula represents a dipole?
..
:S
1)
H
2)
3)
H
:O=C=O:
˙˙
˙˙
4)
H
|
H CH
|
H
.. ..
N≡N
For questions 24-27 use choices a-e. A choice may be used, once, more than once or not at all.
H

HNH
|
H
ammonia
(1)
 
FF
˙˙ ˙˙
fluorine
(2)
|
HCH
|
H
methane
(3)

HO
|
H


O=C=O
carbon dioxide
water
(4)
(5)
___24) Which of the above would be classified as a linear nonpolar molecule made from polar covalent bonds?
___25) Which of the above would be classified as a nonpolar molecule with nonpolar covalent bonds?
26) ____ and ____ Which of the above would be classified as a dipole?
___27) Which of the above would be most similar in shape to a molecule of carbon tetrafluoride?
659
For questions 28 - 35 SELECT FROM AMONG THE CHOICES WHICH DESCRIBE THE VALIDITY OF THE
“ASSERTION” AND THE VALIDITY AND RELATIONSHIP OF THE “REASON”.
ASSERTION
1)
2)
3)
4)
5)
REASON
True
True
True
False
False
True statement and correctly explains or predicts the assertion
True statement but does NOT correctly explain or predict the assertion
False
True
False
For example:
Assertion
Mr. D. has brown eyes
Reason
because
Mr. D. is wearing socks
ANSWER: Both statements are true. However, the wearing of socks has NOTHING TO DO with the
color of Mr. D’s eyes. Therefore, the BEST answer is ‘b”.
ASSERTION
REASON
____ 28. In a nonpolar covalent bond the electrons
are shared equally by two atoms
because
The electronegativity values of the atoms
in a nonpolar bond are identical, no atom has
dominance in attracting the bonding electrons.
____29. NH3 is a nonpolar molecule
because
The molecule NH3 demonstrates an
unequal or asymmetrical distribution of
opposite charge and shape.
____30. The bonds of CCl4 may be classified
as polar covalent bonds
because
Chlorine is a gas at STP and Carbon is a
solid at STP.
____31. Molecules of CCl4 are considered
to be nonpolar molecules.
because
There is a symmetrical distribution of charge
and/or shape in a molecule of CCl4
____32 . A solid at STP is soft, has a low
melting point and is a poor conductor
of electricity. It is probably a
molecular substance..
because
Covalent bonds are the result of the physical
overlap of two atoms s and/or p orbitals.
____33 CaO should conduct electricity when
melted.
because
CaO is an ionic compound and breaks into free
moving ions, when melted. which can conduct a
current
____34 Water has a linear shape
because
There are two possible bonding sites
on an atom of oxygen capable of making
polar covalent bonds.
____ 35 Gold conducts electricity
because
Gold has metallic bonds providing a sea of
mobile (delocalized) electrons capable of
conducting an electrical current.
660
1)
2)
3)
4)
5)
True
True
True
False
False
True statement and correctly explains the assertion
True statement but does NOT correctly explain the assertion
False
True
False
ASSERTION
REASON
_____ 36 The compounds HF and HCl
both have polar covalent bonds
because
All compounds with polar covalent bonds must
be classified as dipoles.
_____ 37 The molecule CI4 is a polar
molecule
because
CI4 is made from nonpolar covalent bonds
_____ 38 Solid Mg conducts electricity
while solid MgO does not
conduct electricity.
because
The sea of mobile electrons responsible for
the bonding in Mg(s) allow for conduction
while the lack of mobility in the electrons of
MgO inhibits conduction.
_____39 The molecule C12H22O11
(table sugar) is a good electrolyte
when dissolved in water.
because
An electrolyte is a general term given to
a substance which dissociates into ions in
solution & can conduct an electrical current.
Answers:
1) 1
2) 3
3) 1
4) 2
5) 1
6) 1
7) 3
8) 4
9) 4
10) 3
11) 2
12) 3
13) 2
14) Oxygen molecules (gas)and Carbon dioxide molecules are nonpolar molecules … while water is a polar
molecule. Like dissolveslike and polar molecules does not efficiently dissolve nonpolar molecules
15) Water is a polar molecule and oil and carbon tetrachloride are both nonpolar molecules. Since Like
dissolves Like, the carbon tetrachloride (old-form of dry cleaning fluid) can remove the oil, while the water can not.
16)
a) Dipole
b) Hydrogen bonding (bonds) Defense _It is a polar molecule, with extensive examples of O or O bonded to H so
it will form Hydrogen bond attractions between itself and water (which has O bonded to H)
c) Urine-based water …. I need to get sufficient Vitamin C every day, because it is so soluble in water
it is eliminated daily.
17) 4
18) 2
27) 3
28. 1
36 3
37 5
19) 4
29. 4
38 1
20) 3
21) 4
30 2
22) 2
31. 1
23) 1
32 2
24) 5
33 1
25) 2
34 4
26) 1 and 4
35 1
39 4
661
GENERAL QUESTIONS REGARDING BONDING AND IMF
1) The bonds between hydrogen and oxygen in a water molecule are classified as
1) polar covalent
2) hydrogen bonds
3) ionic
4) nonpolar covalent
2) Which atom will form an ionic bond with an atom of bromine?
1) nitrogen
2) lithium
3) oxygen
4) carbon
..
3) Given the Lewis Structure: H : F:
¨
The electrons in the bond between hydrogen and fluorine are more strongly attracted to the
1)
2)
3)
4)
hydrogen,
fluorine,
hydrogen,
fluorine,
due to a
due to a
due to a
due to a
higher electronegativity
lower electronegativity
lower electronegativity
higher electronegativity
4) When ionic bonds are formed, metal atoms tend to become
1)
2)
3)
4)
oxidized by losing electrons and become anions
reduced by gaining electrons and become anions
oxidized by losing electrons and become cations
reduced by gaining electrons and become cations
5)
6) Which compound contains both ionic and covalent bonds?
1) CaCO3
2) PCl3
3) MgF2
4) CH3Br
7) Which characteristic is a property of molecular substances?
1)
2)
3)
4)
good thermal energy conductivity
good electrical conductivity
low melting point
high melting point
662
8) A substance that does NOT conduct electricity as a solid, but DOES conduct electricity when fused
(melted), is most likely classified as a(n)
1)
2)
3)
4)
covalent (molecular) compound
nonmetal element
metallic element
ionic compound
9) The bonds of which substance have the greatest ionic character?
1) HCl
3) HF
2) F2
4) Cl2
10) Metallic bonding occurs between species that have seem to have ______________ ionization energies and
experience ________________________
1) high,
a delocalization of valence electrons due to filled inner d orbitals and/or filled
valence orbitals
2) high,
a transfer of valence electrons due to partially filled d orbitals and/or filled
valence orbitals
3) low,
a delocalization of valence electrons due to partially filled inner d orbitals and/or
partially filled valence orbitals
4) low,
a transfer of valence electrons due to filled inner d orbitals and/or filled
valence orbitals
11) At STP, metallic bonding occurs between atoms of:
1) sulfur
2) fluorine
3) hydrogen
4) copper
12) A substance that conducts an electrical current when dissolved in water is called a(n)
1) catalyst
2) metalloid
3) non-electrolyte
4) electrolyte
3) Which pair of atoms will share electrons when a bond is formed between them?
1) Ba and I
2) K and Cl
3) Br and Cl
4) Li and I
663
14) An element with an electronegativity of 0.9 bonds with an element having an electronegativty of 3.1.
Which phrase best describes the bond between these elements? The bond is:
1) mostly ionic in character and formed between two nonmetals
2) mostly ionic in character and formed between a metal and a nonmetal
3) mostly covalent in character and formed between two nonmetals
4) mostly covalent in character and formed between a metal and a nonmetal
15)
The total number of electrons used to bond the two carbons to each other is:
1) 6
2) 2
3) 3
4) 14
16) Covalent bonds are formed when electrons are:
1)
2)
3)
4)
transferred from one atom to another
captured by a nucleus
delocalized into a sea of mobile electrons
shared between two atoms
For questions 17-25 use the following choices:
1)
2)
3)
4)
5)
if only I is correct
if only II is correct
if only I and II are correct
if only II and III are correct
if I, II and III are correct
17) Given the formula H2S it could be determined that a molecule of the compound is:
I)
classified as a polar molecule
II) made from polar covalent bonds
III) “bent “ in shape
18) Given the formula CaF2 it could be determined that
I) it is molecular
II) the electronegativity difference is greater than 1.7
III) it is a solid at STP
664
1)
2)
3)
4)
5)
if only I is correct
if only II is correct
if only I and II are correct
if only II and III are correct
if I, II and III are correct
19) Given the formula CBr4 it could be determined that it is
I) it is molecular made of polar covalent bonds
II) a nonpolar molecule
III) pyramidal in shape
20) Given 1 mol of N2 at STP, it can be determined that
I)
the phase is best explained by London Dispersion Forces
II) it is made from polar covalent bonds
III) the intermolecular forces of attraction are stronger than those found between molecules in 1 mol of Br2
21) Given the formula PH3 you could determine that
I) it is tetrahedral in shape
II) issues regarding normal boiling point are best explained by dipole attractions
III) the compound is made from polar covalent bonds
22) Which sample(s) exhibit(s) stronger intermolecular forces of attraction between molecules, at STP than
those found between the molecules, in a sample of F2 at STP?
I) H2
II) NH3
III) I2
23) Which of the following represent(s) a nonpolar substance?
I) NH3
II) C4H10
III) CO2
24) A chemist performed the same tests on two homogeneous white crystalline solids, A, and B.
Her results are shown in the following table.
Solid "A"
Melting Point
Solubility in water at 0C
(grams per 100g of water)
Electrical Conductivity in
aqueous solution
Solid "B"
935C
68C
35.7
103.2
Good Conductor
Nonconductor
I) Both A and B are made from ionic bonds, primarily
II) Solid A could be an ionic compound
III) Solid B could be a covalent compound
665
Your choice have been repeated for your convenience.
1)
2)
3)
4)
5)
if only I is correct
if only II is correct
if only I and II are correct
if only II and III are correct
if I, II and III are correct
25) The table below lists the results of various tests a chemistry student performed on three different
unknown substances.
The Results of Various Tests on Three Unknown Substances
Characteristic
Unknown 1
Unknown 2
Unknown 3
Solubility in water
insoluble
soluble
Conductivity in aqueous
solution
Conductivity as a solid
not applicable
yes
slightly
soluble
no
yes
none
none
Melting Point
600˚C
802˚C
52˚C
Description
-solid at STP
-crystalline
-high luster
-solid at STP
-crystalline
-brittle
-opaque
-solid at STP
-crystalline
-soft
-white color
Which of the following conclusions is (are) most probable based upon the above data ?
I) Unknown #1 could be a metallic element
II) Unknowns #2 is probably an ionic compound
III) Unknown # 3 could be an ionic compound
666
For questions 26 – 27 use the following choices.
ASSERTION
1)
2)
3)
4)
5)
REASON
True
True
True
False
False
For example:
Assertion
Mr. D. has brown eyes
True statement and correctly explains / predicts the assertion
True statement but does NOT correctly explain / predict the assertion
False
True
False
because
Reason
Mr. D. wears socks
Reasoning: Both statements are true. However, the wearing of socks is unrelated with Mr. D’s eye color.
Therefore, the best answer is "b”.
ASSERTION
26
27
28)
REASON
The intermolecular force of attraction
between the molecules of H2S is
primarily hydrogen bonding
because
CH4 and C8H18 both have ionic bonds.
because
H O
| //
H−C−C − O-H
|
H
bp = 118C
ethanoic acid
H O
| //
H−C−C − O-H
|
Cl
bp = 189C
Hydrogen bonding is strongest between all
molecules in which hydrogen is bonded to
any other nonmetal species.
Methane (CH4) and octane (C8H18 ) are
organic, molecular compounds
Rationalize the differences in the boiling
points, in terms of structure and composition
Place your answer on the answer sheet.
mono-chloro-ethanoic acid
667
ANSWERS TO: GENERAL QUESTIONS REGARDING BONDING AND IMF
1 1) The bonds between hydrogen and oxygen in a water molecule are classified as
(DIFFERENT NONMETALS = POLAR COVALENT)
1) polar covalent
3) ionic
2) hydrogen bonds
4) nonpolar covalent
2 2) Which atom will form an ionic bond with an atom of bromine?
(METAL IONS BONDED TO NONMETAL IONS & Br-1 IS THE NONMETAL
ANION …SO YOU ARE BEING ASKED TO IDENTIFY A METAL)
1) nitrogen
2) lithium
3) oxygen
4) carbon
..
4 3) Given the Lewis Structure: H : F:
¨
The electrons in the bond between hydrogen and fluorine are more strongly attracted to the
1)
2)
3)
4)
hydrogen,
fluorine,
hydrogen,
fluorine,
due to a
due to a
due to a
due to a
higher electronegativity
lower electronegativity
lower electronegativity
higher electronegativity
3 4) When ionic bonds are formed, metal atoms tend to become
1)
2)
3)
4)
oxidized by losing electrons and become anions
reduced by gaining electrons and become anions
oxidized by losing electrons and become cations
reduced by gaining electrons and become cations
3 5)
NONPOLAR COVALENT
BOND IS BETWEEN C & H ….
OR TWO ATOMS OF THE
SAME NONMETAL ELEMENT
TERNARY INORGANIC
COMPOUNDS (THOSE WITH
1 6) Which compound contains both ionic and covalent bonds? POLYATOMIC IONS) TEND TO HAVE
BOTH…. THE NONMETAL ATOMS
1) CaCO3
2) PCl3
3) MgF2
4) CH3Br OF THE PAI ARE BONDED TO EACH
OTHER VIA COVALENT BONDS…
3 7) Which characteristic is a property of molecular substances?
1)
2)
3)
4)
good thermal energy conductivity
good electrical conductivity
low melting point
high melting point
WHILE THE METAL CATION BONDS
VIA AN IONIC BOND TO THE PAI.
668
4 8) A substance that does NOT conduct electricity as a solid, but DOES conduct electricity when fused
(melted), is most likely classified as a(n)
1)
2)
3)
4)
covalent (molecular) compound
nonmetal element
metallic element
ionic compound
3 9) The bonds of which substance have the greatest ionic character?
1) HCl
3) HF
2) F2
4) Cl2
IONIC CHARACTER =
ELECTRONEGATIVITY
DIFFERENCE. LOOK UP
TABLE S AND DO THE MATH
skip 10) Metallic bonding occurs between species that have seem to have ______________ ionization energies
and
experience ________________________
1) high,
a delocalization of valence electrons due to filled inner d orbitals and/or filled
valence orbitals
2) high,
a transfer of valence electrons due to partially filled d orbitals and/or filled
valence orbitals
3) low,
a delocalization of valence electrons due to partially filled inner d orbitals and/or
partially filled valence orbitals
4) low,
a transfer of valence electrons due to filled inner d orbitals and/or filled
valence orbitals
4 11) At STP, metallic bonding occurs between atoms of:
1) sulfur
2) fluorine
3) hydrogen
4) copper
4 12) A substance that conducts an electrical current when dissolved in water is called a(n)
1) catalyst
2) metalloid
3) non-electrolyte
4) electrolyte
3 13) Which pair of atoms will share electrons when a bond is formed between them?
SHARE ELECTRONS = COVALENT BOND … SO YOU ARE LOOKING FOR
TWO NONMETAL SPECIES.
1) Ba and I
2) K and Cl
3) Br and Cl
4) Li and I
669
2 14) An element with an electronegativity of 0.9 bonds with an element having an electronegativty of 3.1.
Which phrase best describes the bond between these elements? The bond is:
1) mostly ionic in character and formed between two nonmetals
2) mostly ionic in character and formed between a metal and a nonmetal
3) mostly covalent in character and formed between two nonmetals
4) mostly covalent in character and formed between a metal and a nonmetal
1 15)
The total number of electrons used to bond the two carbons to each other is:
1) 6
2) 2
3) 3
4) 14
ONE COVALENT
BOND = 2 ETHUS, 3
COVALENT
BONDS EQUAL 6
ELECTRONS
4 16) Covalent bonds are formed when electrons are:
1)
2)
3)
4)
transferred from one atom to another
captured by a nucleus
delocalized into a sea of mobile electrons
shared between two atoms
For questions 17-25 use the following choices:
1)
2)
3)
4)
5)
if only I is correct
if only II is correct
if only I and II are correct
if only II and III are correct
if I, II and III are correct
5 17) Given the formula H2S it could be determined that a molecule of the compound is:
I)
classified as a polar molecule
II) made from polar covalent bonds
III) “bent “ in shape
DRAW THE LEWIS STRUCTURE…2 LONE PAIR
OF ELECTRONS = A BENT SHAPE
& THE BONDS ARE BETWEEN DIFFERENT
NONMETALS (THUS POLAR COVALENT
BONDS) AND IT IS UNEVEN IN SHAPE AND/OR
OPPOSITE CHARGE DISTRIBUTION …THUS A
POLAR MOLECULE (OR DIPOLE)
670
4 18) Given the formula CaF2 it could be determined that
I) it is molecular
II) the electronegativity difference is greater than 1.7
III) it is a solid at STP
IT IS A METAL ION BONDED TO A
NONMETAL ION … SO IT IS IONIC
BONDING (THUS NOT A MOLECULAR
SUBSTANCE)
ALL IONIC COMPOUNDS ARE SOLIDS
AT STP
3 19) Given the formula CBr4 it could be determined that it is
I) it is molecular made of polar covalent bonds
II) a nonpolar molecule
III) pyramidal in shape
1 20) Given 1 mol of N2 at STP, it can be determined that
IT IS TETRAHEDRAL IN SHAPE (4
BONDS …NO LONE PAIR OF EON THE CENTRAL ATOM
IT’S A NONPOLAR MOLECULE
(SO LDF) ….BONDS ARE
NONPOLAR COVALENT….
I)
the phase is best explained by London Dispersion Forces
II) it is made from polar covalent bonds
III) the intermolecular forces of attraction are stronger than those found between molecules in 1 mol of Br2
4 21) Given the formula PH3 you could determine that
DRAW THE LEWIS
STRUCTURE….
I) it is tetrahedral in shape
II) issues regarding normal boiling point are best explained by dipole attractions
III) the compound is made from polar covalent bonds
4 22) Which sample(s) exhibit(s) stronger intermolecular forces of attraction between molecules, at STP than
those found between the molecules, in a sample of F2 at STP?
F2 HAS LDF …AS DOES I2 BUT IT IS
LARGER AND THUS LDF ARE
I) H2
II) NH3
III) I2
STRONGER. NH3 HAS H-BONDING
4 23) Which of the following represent(s) a nonpolar substance?
I) NH3
II) C4H10
III) CO2
DRAW THE LEWIS
STRUCTURES …. EVEN IN
SHAPE AND/OR OPPOSITE
CHARGE DISTRIBUTION IS A
NONPOLAR MOLECULE
671
4 24) A chemist performed the same tests on two homogeneous white crystalline solids, A, and B.
Her results are shown in the following table.
Solid "A"
Melting Point
Solubility in water at 0C
(grams per 100g of water)
Electrical Conductivity in
aqueous solution
Solid "B"
935C
68C
35.7
103.2
Good Conductor
Nonconductor
I) Both A and B are made from ionic bonds, primarily
II) Solid A could be an ionic compound
III) Solid B could be a covalent compound
Your choice have been repeated for your convenience.
1)
2)
3)
4)
5)
if only I is correct
if only II is correct
if only I and II are correct
if only II and III are correct
if I, II and III are correct
3 25) The table below lists the results of various tests a chemistry student performed on three different
unknown substances.
The Results of Various Tests on Three Unknown Substances
Characteristic
Unknown 1
Unknown 2
Unknown 3
Solubility in water
insoluble
soluble
Conductivity in aqueous
solution
Conductivity as a solid
not applicable
yes
slightly
soluble
no
yes
none
none
Melting Point
600˚C
802˚C
52˚C
Description
-solid at STP
-crystalline
-high luster
-solid at STP
-crystalline
-brittle
-opaque
-solid at STP
-crystalline
-soft
-white color
Which of the following conclusions is (are) most probable based upon the above data ?
I) Unknown #1 could be a metallic element
II) Unknowns #2 is probably an ionic compound
III) Unknown # 3 could be an ionic compound
672
For questions 26 – 27 use the following choices.
ASSERTION
1)
2)
3)
4)
5)
REASON
True
True
True
False
False
For example:
Assertion
Mr. D. has brown eyes
True statement and correctly explains / predicts the assertion
True statement but does NOT correctly explain / predict the assertion
False
True
False
because
Reason
Mr. D. wears socks
Reasoning: Both statements are true. However, the wearing of socks is unrelated with Mr. D’s eye color.
Therefore, the best answer is "b”.
ASSERTION
REASON
4 26
The intermolecular force of attraction
between the molecules of H2S is
primarily hydrogen bonding
because
Hydrogen bonding is strongest between all
molecules in which hydrogen is bonded to
any other nonmetal species.
THE IMF IS DIPOLE ATTRACTION…NOT HBONDING … H-BONDING REALLY APPLIES WELL
TO FORCES BETWEEN MOLECULES WITH
H-O, F, N …..NOT S
4 27
28)
CH4 and C8H18 both have ionic bonds.
H O
| //
H−C−C − O-H
|
H
bp = 118C
ethanoic acid
because
H O
| //
H−C−C − O-H
|
Cl
bp = 189C
Methane (CH4) and octane (C8H18 ) are
organic, molecular compounds
Rationalize the differences in the boiling
points, in terms of structure and composition
Place your answer on the answer sheet.
mono-chloro-ethanoic acid
The extra Cl on the mono-chloro-ethanoic acid adds a significantly large number of electrons, which, in
turn help to generate stronger LDF forces between molecules, increasing the energy required to
boil a sample (turn liquid into gas).
LDF while weak, are aggregate in nature, in that more electrons lead to stronger polarizations.
673