CHE 002B Ch. 13 Chemical Bonding

Lewis Bong Theory

simplest way to represent chemical bonding

Valence Electron

electrons in the shell of the highest ‘n’

Ionic Bonds

transfer of electron

Covalent Bonds

sharing of electrons

Single Covalent Bonds

the sharing of one pair of electrons between two bonded atoms

Bond Pair

pair of electrons participating in bonding

Lone Pair

electrons that don’t participate in bonding

Electronegativity (EN)

describes an atom’s ability to compete for electrons

Properties of High EN Elements

• tendency to accept electrons due to large electron affinity

• towards noble gases

Polar Covalent Bonds

electrons are not equally shared

• the greater the EN difference, the greater ionic character of the bond

Formal Charge

shared charge assuming all bond pair electrons are shared equally between atoms

formular: # e - #lone - #bonded/2

Determining Plausible Structures

1. The value must be as small as possible

2. negative formal charges usually on the most EN element

Expanded Octets

occurs in periods 3 or higher elements; can have more than 8 valence electrons

Valence Shell Electron-Pair Repulsion Theory (VSEPR)

1. electron pairs repel each other

2. electron pairs assume orientation about an atom to minimize repulsion

explains shape

Bond Dipoles

a polar covalent bond produces a bond dipole

u = partial charge x distance

• dipole points from less EN to more EN

• the greater the EN difference, the greater the bond dipole

Polarity

the absolute value of the difference in electronegativity between atoms

Polar Molecule

u ≠ 0

Nonpolar molecule

u = 0

Bond Order

the number of chemical bonds between a pair of atoms shared

1. single

2. double

3. triple

Bond Length

the higher the bond order, the stronger the attraction between the atoms and the shorter the bond length

Average Bond Order

fractional bond order is possible for a molecule in which multiple resonance structures are present

Bond order = [(Number of electrons in bonding molecules) - (Number of electrons in antibonding molecules)]/2.

Bond Energies

the average energy required to break a given type of covalent bond

• increases with increasing bond order