1)Molecular Shape and Molecular
Polarity
2)General Types of IMFA
3)Strength of IMFA and Physical
Properties of Matter
4)Effects of IMFA and Practical
Applications
Chapter 3
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§INTERMOLECULAR
FORCES OF ATTRACTION
§This force holds the
molecules together which
can be attractive or
repulsive
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§In combination with the particles’ kinetic energy,
§Intermolecular forces are accountable for
IMFA determine the properties of each phase as
well as phase changes that can potentially take
place.
the existence of different states of matter:
SOLID, LIQUID, GAS
§This are forces that hold IONS together
§IMFAs are relatively weaker than intramolecular
forces that exist within a molecule or ion.
§Strong intermolecular forces tend to yield liquids
and solids;
§Weak intermolecular forces favor formation of
gases.
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§ INTERMOLECULAR FORCES OF ATTRACTION are those
acting in between different molecules or ions.
§ INTRAMOLECULAR FORCES OF ATTRACTION are those acting
between atoms within a single molecule or ion. These include
ionic bonding, covalent bonding, and metallic bonding.
Attractive force
Attractive force
Attractive force
not
And en
e
w
t
be M S!
ATO
What is holding these
molecules?
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Intermolecular Forces
ONLY exist in nonmetals!
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§Exists between ions and a
§Exists between ions and is based on
Coulumb’s law where the force of attraction
between two oppositely charged ions is
directly proportional to the magnitude of the
charges of the ions but inversely proportional
to the distance between the two ions.
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§ Occurs between polar covalent molecules due to the
molecules containing a
hydrogen atom bonded to any
of the most highly
electronegative atoms –
fluorine, oxygen, and nitrogen.
§ This interaction is responsible
for the high boiling point of
water.
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§Occurs between
attraction of the partial positive (δ+) atoms of one molecule
to the partial negative (δ−) atoms of the other molecule. The
interaction between SO2 is an example of the interaction.
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§ Exists between polar
polar compound. The
interaction becomes
stronger as either the charge
of the ion increases or as the
polarity of the molecule
increases. A salt dissolved in
water exhibits this
interaction.
polar covalent and
non-polar covalent
molecules. A
temporary dipole is
created due to the
nearby permanent
dipole.
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§ Often called LONDON DISPERSION
FORCES, after the German-born physicist
Fritz London (1900-1954) who postulated
their existence in 1930.
§ These forces are caused by fluctuations in the electron
distribution within molecules or atoms; consequently, these
forces are present in all molecules and atoms.
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Ammonia (NH3)
Nitrogen Trichloride (NCl3)
Cl
- Dipole- Dipole
- POLAR
(The geometry is
Trigonal Pyramid (1
lone pair); not
symmetrical –
therefore, it’s POLAR)
:
:
:
CH3F, and H2S
Cl
:
Polar and nonpolar molecules
POLAR or
NONPOLAR?
IMFA Type
IMFA Type
:
LONDON DISPERSION
FORCES (LDF)
(weakest)
N
Cl
: :
Dipole-induced dipole
POLAR molecules
NH3, HF,
CH3OH
:
DIPOLE-DIPOLE
POLAR molecules containing H, chemically
bonded to F, O, and N
EXAMPLES
Mg2+, Cl1-, K1+
Ca2+ and PCl3
: :
H-BONDING
(strong)
INTERACTING SUBSTANCES
IONS only
Ions and polar molecule
:
TYPE OF IMFA
Ion-Ion
Ion-Dipole
POLAR or
NONPOLAR?
H
- LDF
N
H
Hl and CH4
H
- POLAR
(The geometry is
Trigonal Pyramid (1
lone pair); not
symmetrical –
therefore, it’s POLAR)
- H-Bonding
(since the Hydrogen atom is
chemically bonded to Oxygen
atom)
- Dipole- Dipole
- LDF
All molecules, whether POLAR or NONPOLAR
In general, however, dipole–dipole interactions in small polar molecules are significantly stronger than London dispersion forces, so the former predominate
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Compound
1.) Carbon Tetrachloride
3.) Water
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2.)Xenon Tetrafluoride
4.) Sulfur Hexafluoride
5.) Hydrogen Bromide
POLAR or
NONPOLAR
IMFA Type
1.)
2.)
3.)
4.)
5.)
1.)
2.)
3.)
4.)
5.)
1)Molecular Shape and Molecular
Polarity
2)General Types of IMFA
3)Strength of IMFA and Physical
Properties of Matter
4)Effects of IMFA and Practical
Applications
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Hydrofluoric
Acid (HF)
Ammonia
(NH3)
§Both non-metal
§H is bonded to F
§ΔEN 0.96–POLAR
§ ΔEN 1.78–POLAR
§Dipole-Dipole
§Dipole-Dipole
§LDF
§H-bonding
Hydrochloric
Acid (HCl)
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§Both non-metal
§LDF
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Physical properties of substances
especially for the condensed states
(liquid and solid) vary significantly
depending on the nature and strength
of the attractive forces among atoms,
molecules, or ions.
§Both non-metal
§H is bonded to N
§Not symmetrical –
POLAR
§Dipole-Dipole
BOILING
POINT
§H-bonding
§LDF
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MELTING
POINT
VISCOSITY
POINT
VAPOR
PRESSURE
SURFACE
TENSION
§The melting point of a substance is the temperature
at which its solid and liquid phases coexist in
equilibrium.
§Is the resistance to flow of a liquid
§The freezing point of
water is the same as the
melting point of ice:
32°F (0°C)
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§The vapor pressure of a
increase the surface area by a
unit amount.
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§The boiling point of a liquid is the
substance is the pressure
exerted by its vapor state and
reflects the escaping tendency
that indicates a liquid’s
evaporation rate.
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§Is the energy required to
temperature at which its vapor
pressure equals the atmospheric
pressure
§Addition of heat results in the
transformation of the liquid into its
vapor.
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Water
Melting Point,
Viscosity,
Surface Tension
Ethene
Strong
IMFA
Boiling Point
High Boiling
Point!
Low Boiling
Point!
Low
Vapor
Pressure
High
Boiling
Point
Strength of
IMFA?
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ACTIVITY 1: Identify the ONE with the higher boiling point (BP), melting point (MP), viscosity (V),
surface tension (ST), and vapor pressure (VP).
Molecules
BP
MP
V
ST
VP
§ Boiling point, melting point, viscosity, and surface tension
increases with increasing strength of intermolecular
forces. On the other hand, vapor pressure increases with
decreasing strength of intermolecular forces.
Dihydrogen Sulfide vs Water
§ If all other variables are CONSTANT, the LDF increases with
Methanol vs Ethanol
increasing molar mass.
q Example: I2 (molar
mass= 126.9 g/mol x 2 = 253.8 g/mol) has a higher
boiling point than Cl2 (molar mass = 35.45 g/mol x 2 = 70.9 g/mol)
Carbon Tetrachloride vs Methane
q MOLAR MASS IS EQUAL TO THE ATOMIC MASS OF THE ELEMENT
§ However, substances that form HYDROGEN BONDS have
much higher Boiling Point, Melting Point, Viscosity, and Surface
Tension than one would predict based on molar mass.
Acetic Acid vs Acetone
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1)Molecular Shape and Molecular
Polarity
2)General Types of IMFA
3)Strength of IMFA and Physical
Properties of Matter
4)Effects of IMFA and Practical
Applications
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Medical implants and
prostheses are
designed to aid a
person by acting as a
substitute to a missing
part, support an injured
structure, or improve
an existing part of the
body.
Artificial pacemaker
§ Type of breast implant depends on the filler material;
§Materials used in making implants &
Dental implants
Cochlear grafts
Breast implants
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some have saline solution as the filler, while others
have silicon gel.
prostheses should be inert to avoid adverse
reactions in the body. Most importantly,
implants for support must have strong IMFA to
be durable. The basis of material selection in
making objects depends on the strength it
confers.
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§ SALINE-FILLED IMPLANTS – ion-dipole exist; saline
consists of salt, which in turn is made up of cations and
anions dissolved in water.
§ SILICON GEL-BASED IMPLANTS – dipole-induced
dipole IMFAs are present, since silicon is a semi-metal.
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§ For electronic devices and household gadgets, dipole-
induced dipole exists since components of such
devices include polar substances like transient voltage
suppression diodes and metalloids or semi-metals
capable of having induced dipole.
§ Sports equipment are materials used for exercise or
Property (strong,
moderately, strong,
weak)
IMFAs
Electronic Devices
Semi-metals
Moderately strong
Dipole-induced
dipole, induced
dipole-induced dipole
Construction
Materials
Sand, gravel, rocks,
water, cement
ü Carbohydrates
ü Lipids
ü Nucleic Acids
ü Proteins
Sports Equipment
sports activities. These apparatuses must be durable;
hence the need for strong IMFAs.
§ Construction supplies, due to the required strength
from their components (sand, gravel, rocks, water,
cement), have the following IMFAs consequently:
ion-ion, H-bonding, dipole-dipole, and ion-dipole.
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Composition (type of
atom/ polarity)
MATERIALS
Household Gadgets
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§ Like in water, carbohydrates have oxygen atoms connected to
hydrogen atoms (o-h bonds) also known as hydroxyl groups;
therefore, carbohydrates exhibit hydrogen bonding.
§ CARBOHYDRATES are the most abundant type
of organic macromolecules on Earth. These are
sugar polymers, and the term carbohydrate was
coined from the atom carbon plus water, meaning
hydrated carbon.
§ Examples include starch in potatoes, rice and pasta,
sucrose in sweets and soft drinks, fructose in honey,
maltodextrins in sports drinks, glycogen in meat,
cellulose in indigestible fiber as well as lactose in
milk.
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Monosaccharide
(Glucose)
Polysaccharide
(Amylose starch)
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§ Cell walls of plants
have cellulose as
the major
component.
§ Hydrogen bonds
between hydroxyl
groups of glucose
monomers hold
parallel cellulose
molecules together.
§ Carbohydrates can have structural and storage functions. It
serves a structural purpose in cell walls of plants and
bacteria; where cellulose is present in plant cells, while
peptidoglycan in bacterial cell wall.
§ The strength from hydrogen bond confers the firm
structure of plant and bacterial cell walls; hence their
structural functions.
§ Cellulose is the component of plant cells difficult to digest by
humans.
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Disaccharide
(Sucrose)
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§In cell membranes, carbohydrates perform
membrane function as glycophorin and mucin.
§Glycophorin is a transmembrane glycoprotein in
red blood cells.
§Mucin is the most abundant macromolecules in
mucus; important for lubrication, protection and for
moisture maintenance.
§Carbohydrates are also used as storage of energy.
ü Starch - stored form of carbohydrates in plants;
ü Glycogen - stored form of carbs in animals.
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§ LIPIDS are a group of organic molecules found in
biological systems that are insoluble in water but
soluble in nonpolar solvents.
§ Two types of lipids: those that contain fatty acid
(fats, oils, waxes, etc.) and those that do not contain
fatty acid (steroid, cholesterol, terpenes, etc.).
Components of a fatty acid include a polar head and a long
chain nonpolar hydrocarbon tail.
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§ Fatty acids spontaneously
§ The polar head consists of a carboxyl group
form micelles when
immersed in POLAR
substance since fatty acids’
polar heads can interact
with a POLAR medium such
as water ion-dipole via
HYDROGEN bonding or
DIPOLE-DIPOLE
interaction; and the
NONPOLAR tail can interact
with another NONPOLAR
substance or with another
NONPOLAR tail.
§ IMFAs present are therefore hydrogen bonding for the hydroxyl
group (
) and dipole-dipole for carbonyl group (
).
§ The tail is composed of long chain nonpolar aliphatic chain; hence,
London Dispersion forces are prevailing .
§ Fatty acids are consequently amphiphilic by virtue of having a polar
head and a nonpolar tail.
§ There are several types of IMFAs present in a fatty acid; but which shall
determine the overall characteristics of the molecules?
§ From the figure, the major IMFA present is expected to be London
dispersion forces, specifically hydrophobic interactions between the
nonpolar tails; since the nonpolar hydrocarbon tail is much more prominent
than the small polar head.
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§ When grease or oil (nonpolar hydrocarbons) mixes with
the soap-water solution, fatty acids act as bridge between
polar water molecules and nonpolar oil molecules. Since
fatty acids in soap have both polar and nonpolar portions,
the soap act as an emulsifier.
§ EMULSIFIER – allows normally immiscible liquids to mix.
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§IMFAs between
§ NUCLEIC ACIDS are
§ From the charged phosphate,
polymers of several
nucleotide residues. A
nucleotide consists of a
nitrogenous base, sugar,
and phosphate.
ion-ion.
§ From the oxygen & hydroxyl
(-OH) groups in the sugar,
dipole-dipole & H-bonding.
§ In nitrogenous base, H-
§ the main chain of nucleic
bonding (from NH 2) &
dipole-dipole (from nitrogen
atoms) are likely.
acids consist of a sugarphosphate backbone; the
side chains consist of
nitrogenous bases.
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nitrogenous bases
determine the folding
of the sugar-phosphate
backbone to yield a
specific conformation,
such as double helix in
DNA (deoxyribonucleic
acid), consequently
providing the
framework for overall
three-dimensional
shape of nucleic acids.
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§FIVE NITROGENOUS BASES:
1)Adenine ( A )
2)Guanine ( G )
3)Cytosine ( C )
4)Uracil ( U )
5)Thymine ( T )
Adenine (A) can form two
hydrogen bonds with either
Thymine (T) or Uracil (U).
§PROTEINS are the most abundant type of
molecules in the body. Each protein performs
specific function.
§Protein molecules have roles in catalysis,
muscle contraction, gene regulation, hormone
regulation, immunity, structure, and transport.
Guanine (G) can form three Hbonds with Cytosine (C );
hence, a nucleic acid rich in
G-C nucleotides are more
resilient.
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§ AMINO ACIDS are the building blocks of
proteins.
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§Without these IMFAs in proteins, the skin,
§ Amino
group,
has Hbonding
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§ Depending on
the type of
side chain,
other forces of
attraction can
also be
present
hair, nails, and cartilages would easily be
frail.
§In medical standpoint, for instance, if
there is less hydrogen bonding for
stabilization, scurvy is a consequence;
this results to abnormal bone growth and
poor wound healing.
§ The carboxyl
group (COOH) has
H-bonding
and dipoledipole IMFAs
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§
Answer all the questions on your data notebook.
1) What are the evidences of chemical change?
2) Is it possible to control the rates of a chemical reaction?
How?
3) What are the forms of energy that can be observed when
you burn a paper?
4) Where does the energy during a chemical reaction come
from?
5) What are some examples of renewable energy sources?
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