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 right arrow M(g)+ + e-

X(g) + e- right arrow X(g)- + energy

M(g)+ X(g) right arrow MX(g)




















Lewis Structures for Atoms


 Lewis Structure

Kernel electrons 

Valence electrons



 1s2 2s2 2p6



 phosphorus Lewis dot structure

 1s2 2s2 2p6

 3s2 3p3


 bromine Lewis dot structure

 1s2 2s2 2p6 3s2 3p6 3d10

(≠ [Ar] = 1s2 2s2 2p6 3s2 3p6 )










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