Chemical Bonding. Chemical Bonds Compound are formed from chemically bound atoms or ions Bonding only involves the valence electrons.

Covalent Bonding

• What’s going on?• Molecule – formed when 2 or more atoms

bond covalently

Sharing of electrons

Two Types of Covalent Bonds

i) nonpolar covalent – equal sharing of e-

ii) polar covalent – UNequal sharing of e-

Nonpolar vs. Polar

NONPOLAR POLAR

Nonpolar vs. Polar

Nonpolar vs. Polar

Predict these shapes

N••

HH

H

NH3

trigonalpyramidal

H2O CO2

O••

••H H

bent

C••••O O

••••

linear

Using electronegativity to determine bond type• Recall electronegativity: how much an

atom wants electrons

• Each atom is assigned a number between 0-4.0 to determine electronegativity strength

• We know 3 types of bonds:

- nonpolar covalent

- polar covalent

- ionic

• To determine bond type, subtract electronegativity values and see scale

Using electronegativity to determine bond type

Scale

0 4.01.70.3

polarcovalent

nonpolarcovalent ionic

H-H

H-O

2.2 – 2.2 = 0

3.44 – 2.2 = 1.24

nonpolar

polar

H-C 2.55 – 2.2 = 0.35 polar

K-F 3.98 – 0.82 = 3.16 ionic

Dipole Moment

• defn – imbalance of electron density in a covalent bond– Due to electronegativity of atoms

- (partial negative) = signifies more EN atom

+ (partial positive) = signifies less EN atom

= shows direction of dipole moment

Examples

H = 2.2C = 2.6N = 3.0Cl = 3.2O = 3.4F = 4.0

H O+ -

Cl C- +

N H- +

C F+ -

Intermolecular Forces

• Defn – attractive forces between 2 molecules; weak compared to bonds

Intermolecular Forces

• London Dispersion Forces – very weak, exist in all molecules due to temporary shifts in the electron cloud

Electrons evenly distributed

Temporary dipole

London force

Intermolecular Forces

• Dipole-Dipole – attraction between oppositely charged regions of polar molecules

+ - +

-+

-

Intermolecular Forces

• Hydrogen Bonding – special type of dipole-dipole occurring btwn molecules that have a H bonded to either a N,O, or F of another molecule; strongest force

- Water is prime example

OHH

O

+ +

-

OHH

O

OHH

O

OHH

O

OHH

O OHH

O

hydrogenbond

+ +

-

+ +

-

Strength Ranking

Hydrogen > dipole-dipole > London