Formation of ionic bonds

We can visualize the formation of ionic bonds as the transfer of an electron from a metal atom to a non-metal atom to form an ion pair. in vacuo:

M_(g) + energy M_(g)⁺ + e^-

X_(g) + e^- X_(g)^- + energy

M_(g)+ X_(g) MX_(g)

• Example: 2 Na + Cl₂ NaCl.
  • Na + energy Na⁺ + e^-
  • Cl + e^- Cl^- + energy
  • Na⁺ + Cl^- NaCl + H

  Movie of NaCl formation from free atoms: Na + Cl NaCl

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Lewis Structures for Atoms

Name	Lewis Structure	Kernel electrons	Valence electrons
Sodium	Na.	1s2 2s2 2p6	3s1
Phosphorus		1s2 2s2 2p6	3s2 3p3
Bromine		1s2 2s2 2p6 3s2 3p6 3d10 (≠ [Ar] = 1s2 2s2 2p6 3s2 3p6 )	4s24p5

 

 

 

 

 

 

 

 

Formal Charge (FC) = the charge an atom would have if all bonding pairs were shared equally (polar bonds don't exist in this model).

To assign Formal Charges:

1. Draw a correct Lewis Structure.

2. Assign both electrons of a lone pair to its associated atom.

3. Divide all bonding pairs, giving one electron of each pair to each atom in the bond.

4. Calculate FC = # electrons on the unbonded (elemental) atom - # electrons assigned to the bonded atom.

 

 

 

 

 

© R A Paselk

Last modified 3 April 2015