1. Unit 4
Bonding Theories

2. O = O O = O VSEPR Theory Valence Shell Electron Pair Repulsion
Predicts the shapes of covalent molecules
The repulsion between electron pairs causes molecular shapes to adjust so that the valence-electron pairs stay as far apart as possible.
O = O
O = O

3. - - Molecular Shapes 180o 120o 104.5o 109.5o 107o SHAPE DESCRIPTION
ILLUSTRATION
Linear
Bond Angle = 180o
One or two bonding pairs, no lone pairs X A
180o X A
104.5o
Bent
Bond Angle = 104.5o
Two bonding pairs, two lone pairs X A
107o X A
120o
Trigonal Planar
Bond Angle = 120o
3 bonding pairs, no lone pairs X A
109.5o
Trigonal Pyramidal
Bond Angle = 107o
3 bonding pairs, one lone pair
Tetrahedral
Bond Angle = 109.5o
Four bonding pairs, no lone pairs

4. Lone Pairs
Take up MORE space
SQUEEZE the bond angle X A X A

5. HF CH4 Practice: Determine the shape of each molecule: LINEAR
TETRAHEDRAL

6. More Practice: BF3 NH3 SeCl2 TRIGONAL PLANAR TRIGONAL PYRAMIDAL BENT F

7. Bond Polarity A B Due to differences in ELECTRONEGATIVITY,
Equal & Unequal Sharing of Electrons
Shared Electron Pair A B 
Due to differences in ELECTRONEGATIVITY,
the sharing of electrons is not always equal between the atoms.

8. Electronegativity
Electronegativity (EN) is the ability of an atom to attract electrons
F=largest electronegativity
Atoms with the largest electronegativity attract electrons more strongly than those with a small electronegativity.

9. Periodic Table of Electronegativities
Why are the Noble Gases not listed?

10. Nonpolar Covalent Bonds
Bonding electrons are shared equally.
Examples: H2, CO2, BF3, CH4
GUIDELINES FOR IDENTIFYING A NONPOLAR BOND:
If only two atoms involved, both atoms are identical.
NO lone pairs are on the central atom.
All atoms bonded to the central atom are the same.
The bond types are identical around the central atom.

11. = = NONPOLAR COMPOUNDS F H B H C BOTH ATOMS ARE IDENTICAL
ALL ATOMS BOUND TO CENTRAL ATOM ARE THE SAME
BOTH ATOMS ARE IDENTICAL
BOND TYPES ARE IDENTICAL AROUND CENTRAL ATOM
NO LONE PAIRS ON CENTRAL ATOM H C
= = O C
BOND TYPES ARE IDENTICAL AROUND CENTRAL ATOM
ALL ATOMS BOUND TO CENTRAL ATOM ARE THE SAME
NO LONE PAIRS ON CENTRAL ATOM
WHAT MAKES THIS A NONPOLAR COMPOUND?

12. Polar Covalent Bonds Bonding electrons are shared unequally.
Examples: HCl, H2O, HCN, PBr3, CH3F
GUIDELINES FOR IDENTIFYING A POLAR BOND:
If only two atoms involved, both atoms are different.
Lone pairs are on the central atom.
At least one atom bonded to the central atom is different from the rest.
There is more than one bond type around the central atom.

13. THERE ARE MORE POLAR COMPOUNDS THAN THERE ARE NONPOLAR!Br H Cl
ATOMS ARE DIFFERENT
THERE ARE MORE POLAR COMPOUNDS THAN THERE ARE NONPOLAR!
LONE PAIRS ON CENTRAL ATOM O H H C F
LONE PAIRS ON CENTRAL ATOM
ATOMS BOUND TO CENTRAL ATOM ARE NOT THE SAME
DIFFERENT BOND TYPES AROUND CENTRAL ATOM C H N
WHAT MAKES THIS A NONPOLAR COMPOUND?

14. Electronegativity Differences
Another way to determine the polarity of a bond is by determining the difference in electronegativity (ΔEN) of two atoms.
Electronegativity Differences & Bond Types:
IONIC: ΔEN > 1.7
POLAR COVALENT: 0.4 < ΔEN ≤1.7
NONPOLAR COVALENT: ΔEN ≤ 0.4
ΔEN = Ι EN atom 1 – EN atom 2 Ι

15. PRACTICE: H – F N – O C – H Si – P B – Cl Ι 2.1-4.0Ι = 1.9 IONIC
Determine if the bond is IONIC, POLAR, or NONPOLAR:
H – F
N – O
C – H
Si – P
B – Cl
Ι Ι = 1.9 IONIC
Ι 3.0 – 3.5 Ι = 0.5 POLAR
Ι 2.5 – 2.1 Ι = 0.4 NONPOLAR
Ι 2.1 – 1.8 Ι = 0.3 NONPOLAR
Ι 2.0 – 3.0 Ι = 1.0 POLAR

16. So What Does It Mean To Be Polar?
EXPLAINATION:
EXAMPLE:
In a polar bond, the more electronegative atom attracts electrons more strongly & gains a slightly negative charge.
The less electronegative atom has a slightly positive charge.
Chlorine is the more electronegative atom
POSITIVE
NEGATIVE H Cl

17. DIPOLES
A molecule that has two poles is said to be a dipolar molecule or DIPOLE.
Two poles have been created
positive pole & negative pole
When placed between oppositely charged plates, they tend to orientate with respect to the positive & negative plates.
POSITIVE
NEGATIVE H Cl

18. Intermolecular Forces
Are weaker than either ionic or covalent bonds.
Types of Intermolecular Forces:
Hydrogen Bonds
Van der Waals Forces
Dipole Interactions
Dispersion Forces

19. Hydrogen Bonds
Attractive forces in which a hydrogen covalently bonded to a very electronegative atom is also weakly bonded to an unshared electron pair of another electronegative atom.

20. Properties of Hydrogen Bonds
Hydrogen bonds are very easy to break
5% the strength of a covalent bond
Strongest of the intermolecular forces
Water molecules are held together
by hydrogen bonds.
Hydrogen bonding accounts for
many properties of water.
Liquid at room temperature
Cohesive properties

21. Van der Waals Forces Dipole Interactions Dispersion Forces
Occur when polar molecules are attracted to one another
Like Hydrogen bonds, but with other atoms
Dispersion Forces
Weakest of all molecular interactions
Caused by the motion of electrons of a molecule when close to a neighboring molecule