Try these..
• Mg
• CaCl2
• H2S
Double and Triple Bonds
Example: HCN
Make a table:
atom
have
need
H
1
2
C
4
8
N
5
8
total
10
18
Difference: 18-10=8 divide by 2 = 4
You need 4 bonds in this structure
Sharing 4 or 6 electrons (Double or Triple bonds
allow this to happen)
Electron dot drawings for polyatomic ions
Always include brackets and charges, but have covalent
bonds inside the ion
Count the number of valence electrons for each and the add
or subtract and electron to make the correct charge
NH4+
OH-
SO42Draw NH4OH
Why is water so unique?
Why Can water bugs run across a pond?
Why does water have such a high boiling point?
Why can we live on earth?
Why is water attracted to a – charge?
Why is Hexane not attracted?
In this unit we will be able to
understand how the Chemical
Bonds in a substance determine
physical properties
• Why water is so unique
• How the bonds that compose a substance
determine the properties within
• How shampoo works
• How household cleaners work effectively
Lets set up your Lab Book
• Purpose: To study the physical properties of
common solids and to investigate the
relationship between the type of bonding in a
substance and its properties.
– Volatility
– Melting Point
– Solubility
– Brittleness
– Conductivity
• Procedure: See Handout
• Volatility-Waft the substance
• Solubility (Hexane and Water) in well plate
• Conductivity (RED &GREEN LIGHT MEANS
CONDUCTIVE)
• Melting Point Watch Glass on beaker of water and
test tube in bunsen burner
• Brittleness (MORTAR AND PESTLE STATION)
Data
• Record Observations in Table
Disposal
• Rescue Aluminum if possible
• Rinse out Sand in Garbage
• Everything else can go down Sink
What did you discover in the periodic
properties lab?
• Which substance was the most volatile?
• Which substances had the lowest melting
point?
• Which substances conducted electricity?
• Which substances dissolved in water? Hexane?
• Which substances do you believe had the
strongest bonds? Why?
• Which substances do you believe have the
weakest bonds? Why?
• How do you determine the types of bond that
exist in a compound?
• What is electronegativity?
• For the following molecules,and ionic
compounds
• Draw the Lewis Dot Structure
• CaS
• AlCl3
• BH3
Electron dot drawings for polyatomic ions
Always include brackets and charges, but have covalent
bonds inside the ion
Count the number of valence electrons for each and the add
or subtract and electron to make the correct charge
NH4+
OH-
SO42Draw NH4OH
Exceptions to the octet rule
1. Metals
MgH2
BH3
3. Some Nonmetal atoms
because of their size, they can have more than an
octet of electrons (due to the presence of empty “d”
orbitals which can be used for bonding).
SF6
PCl5
DON’T FOCUS ON THESE BUT KNOW THEY OCCUR!
Try these….
• Mg(OH)2
C3H6
O2
Note:
• Not all covalent bonds have equal sharing of
electrons
• There are electron hogs!!! Elements that hold
on to the electrons more tightly than others
• You can determine if a bond is ionic,covalent
and if there is an electron hogs, through
looking at a characteristic property.
When the ΔE.N. is less than 2.0, the bond is covalent
Examples: The O-H Bond in H2O
The N-O Bond in NO2
• This means the electrons spend more time around one of the
elements giving it a partial charge
• Draw a picture of how you think the electrons would be
distributed for an OH bond and a NO bond
When the electrons are shared equally
ex: H-H bond
NCl Bond
the bond is pure covalent and has no partial charge
Draw a picture that describes what this would look like
Why do you think there would not be a partial charge on these
bonds?
The type of bond can usually be calculated by
finding the difference in electronegativity of the two
atoms that are going together.
Electronegativity
Difference
• If the difference in
electronegativities is
between:
– 2.0 to 4.0: Ionic
– Covalent Bonds
– 0.1 to 1.9: Polar Covalent
– 0.0: Non-Polar Covalent
Example: NaCl
Na = 0.8, Cl = 3.0
Difference is 2.2, so
this is an ionic bond!
These bonds are called intramolecular
forces
• Have various strengths
– Ionic (STRONGEST)
– Polar Covalent (NEXT STRONGEST)
– Covalent (STRENGHTH DEPENDS ON
ELECTRONEGATIVITY DIFFERENCE)
Bond Polarity
HCl is POLAR because it
has a positive end and a
negative end. (difference
in electronegativity)
+d -d
••
••
H Cl
••
Cl has a greater share in
bonding electrons than
does H.
Cl has slight negative charge (-d) and H has slight
positive charge (+ d)
Bond Polarity
This is why you can dissolve Glucose in water
and not hexane…
Glucose is charged thus will be attracted to
the charged bonds in water
Today we’re Putting it all together!
• Why do substances have the properties that
they do?
• How can I predict the physical state of a
substance?
Draw the Lewis Dot and Predict the
shape for
• I2
• SO42• TeBr2
The difference between polar bonds
and polar molecules
• Polar bonds have a electronegativity
difference between 2 atoms
• Polar molecules
– Include a polar bond
– Have an asymmetrical shape
• Is NH3 a Polar Molecule?
– Yes! Why?
Is CCl4 a polar molecule? Why?
Does it have a polar Bond? Yes
Do it have an asymmetrical shape? NO!!!
Thus it is not a polar molecule.
What about CO2
Does it have a polar bond?
Is it asymmetrical? NO
Thus it is not a polar molecule..
Intermolecular Forces
and
Bonding in Solids
What holds molecules together?
What holds several molecules together?
How does this relate to Properties?
Intramolecular
Forces (Those bonds that hold molecules or
compounds together internally) vs.
Intermolecular Forces (Those forces that exist
BETWEEN molecules).
Intermolecular Forces
Intermolecular forces are forces between molecules
(Intermural sports are between different schools).
Intramolecular forces hold atoms together in a molecule. Intramural
sports are competition at a specific school.
Intermolecular vs Intramolecular
•
41 kJ to vaporize 1 mole of water (inter)
•
930 kJ to break all O-H bonds in 1 mole of water (intra)
Generally,
intermolecular
forces are much
weaker than
intramolecular
forces.
“Measure” of
intermolecular force
boiling point
melting point
Types of intermolecular Forces
• Dispersion Forces
Weak Intermolecular Forces (In Non Polar
Bonds)
• Dipole-dipole interactions (In Polar Bonds)
• Hydrogen bonds (Bonds between H and F,O,N Ex:
H2O, NH3
• Relative strength of Intermolecular Forces:
– Weakest to strongest: dispersion forces, dipole-dipole,
hydrogen bonds
– All are much weaker than intramolecular forces
(covalent bonds,ionic bonds or metallic bonds)
What type of Intermolecular Forces
exist
• In Non Polar molecules
• Dispersion Forces
• In Polar Molecules
• Dipole Dipole Forces, dispersion forces and sometimes
Hydrogen Bonds
Intermolecular Forces
What type(s) of intermolecular forces exist between each of
the following molecules?
CH4
CH4 is nonpolar: dispersion forces.
S
SO2
SO2 is a polar molecule: dipole-dipole forces. There are also
dispersion forces between SO2 molecules.
HF
HF is a polar molecule: dipole-dipole forces. Hydrogen is
bounded to F. Hydrogen bonds exist. There are also dispersion
forces between HF molecules.
How does mass affect dispersion
forces?
Boiling Points of Group IV Hydrides
Which molecule will have a lower
boiling point?
AsH3 or PH3? Why?
Molecule Polarity
• “Like Dissolves Like”
– Polar dissolves Polar
– Nonpolar dissolves
Nonpolar
How do I put all this information
together?
1. Determine if a Substance is a Ionic
Compound or Molecule
2. If the substance is a molecule,determine if it
is polar
3. Look the type of intermolecular forces in the
molecule
4. Look at the Mass of the substance
Why does water have the qualities
that it does?
• What types of bonds?
• What types of intermolecular forces at room
temperature?
• Why types of substances will dissove in water?
• Will NaCl dissolve in water?
• Will NaCl dissove in hexane?
• Will Lauric acid dissolve in water?
• Will Lauric acide dissolve in hexane?