1. Molecular Shapes Electron pairs are negative and repulse each other.
valence-shell electron-pair repulsion theory (VSEPR)
States that molecules will achieve a 3-dimensional shape in order to push electron-pairs as far away from each other as possible
Shape 1: Linear
electron pairs force bonds to be 180º from each other
Ex: Any molecule with only two atoms
CO2
Shape 2: Bent Linear
Two pairs of unshared electrons push the bonds into a bent shape
Example: H2O 1

2. Molecular Shapes Shape 3: (Trigonal) Pyramidal
A single pair of unshared electrons push bonds away into a pyramidal shape
Example: Ammonia, NH3
Shape 4: Tetrahedral
With a central atom that bonds 4 times(Carbon), the bonds are spaced out equally.
Example: Methane, CH4 2

3. Molecular Shapes Shape 5: Trigonal Planar
A central atom bonded to three elements with no unshared pairs of electrons.
Shape is triangular and flat
Examples: BH3, CH2O 3

4. Molecular Polarity When Determining Polarity:
Ask: Are the bonds polar/nonpolar?
Ask: Is there symmetry?
Ask: What shape is it?
Nonpolar molecules have symmetry.
no positive/negative end
charge is evenly distributed
Examples: Diatomic molecules(BrINClHOF), CH4, CO2
Polar molecules do not have symmetry
Linear, trigonal planar and tetrahedral shapes can be polar if there is no symmetry
Bent linear and pyramidal shapes are always polar 4

5. Physical Properties of Molecules
Molecule- compounds that are formed by covalently bonded elements
Molecules tend to be
soft or brittle
Poor conductors of heat & electricity
low melting points
Many are gases or liquids at room temperature
Intermolecular Forces of Attraction
Determines the phase of molecules(solid, liquid or gas)
Relatively weak compared to ionic compounds
Dipole-dipole forces- polar molecules tend to “stick” to each other because of their positive-to-negative bonding.
Van der Waals Forces- non-polar molecules have a weak attraction to each other
Dipole-dipole forces are stronger than Van der Walls forces
both are very weak compared to ionic compounds 5

6. Naming Binary Molecules
Step 1: Determine if ionic or molecular. If it starts with a metal, see ionic rules for naming.
Step 2: The most metallic(closer to francium) atom is written first
Step 3: The least metallic (closer to flourine) atom is written second & ending is changed to “-ide.”
Step 4: Add prefixes to indicate how many of each element is in the formula. Mono is only used for the second element.
CO2 = carbon dioxide
Examples:
SO2
CCl4
N2H4
# atoms
Prefix 1
Mono 2 di 3
tri 4
tetra 5
penta 6
hexa 7
hepta 8
octa 9
nona 10
deca
sulfur dioxide
carbon tetrachloride
dinitrogen tetrahydride 6

7. Physical Properties of Molecules
“Like dissolves like”
Polar molecules dissolve polar molecules
Nonpolar molecules dissolve nonpolar molecules
But nonpolar and polar do not mix!
It's like oil and water. Well, it is oil(nonpolar) and water(polar)! 7

8. Physical Properties of Molecules
Ionic compounds can dissolve in polar liquids
Polar molecules surround the ions
positive end-to-anion
Negative end-to-cation
Compounds with Both ionic and Covalent bonds
Polyatomic ions are made with covalent bonds
Bonds between nonmetals are covalent
Bond with the metal is ionic. 8