Bonding Models
Lewis Structure
G. N. Lewis (UC, Berkeley, 1915)
Octet Rule: Closed shell configuration of 8 surrounding e
Chemical Bonding
Chemical Bonding
Why do bonds form between atoms? extra nuclear/electron attraction - more space for electrons
to move around in to avoid each other
Localized bonding - 2e- bonds - Lewis dot structures used to represent bonding - octet rule.
Rules for determining Lewis dot structures of molecules:
1. Calculate total #electrons necessary to complete octets of all atoms (duet in the case of hydrogen and
the alkali metals). Ex. CO2 requires 24 e-.
2. Calculate total # valence electrons available. Subtract this number from the number in part 1) and
divide by 2 to get # of bonds. You may have to form multiple bonds between atoms.
Ex. CO2 has 4+6+6=16 e- ; it should have (24-16)/2 = 4 bonds.
3. To arrange atoms in a molecule, in general, place unique atom in the middle. More
electronegative atoms and hydrogen go on the outside since the require fewer electrons, hence
fewer bonds, to complete their octets.
O C O
Lewis Dot Model
A quick method for determining the arrangement of atoms in a molecule from its molecular formula
4. The most stable structures have the largest sum of electronegativity differences for adjacent
atoms. E.g HOCl vs. HClO
Sum of differences 2.05 1.31
H O Cl H Cl O
Electronegativity 2.30 3.61 2.87 2.30 2.87 3.61
Differences 1.31 0.74 0.57 0.74
