What do valence electrons have to do with bonding?

1 Answer
May 19, 2014

The valence electrons are the electrons that determine the most typical bonding patterns for an element.

These electrons are found in the s and p orbitals of the highest energy level for the element.

Sodium #1s^2 2s^2 2p^6 3s^1#
Sodium has 1 valence electron from the 3s orbital

Phosphorus #1s^2 2s^2 2p^6 3s^2 3p^3#
Phosphorus has 5 valence electrons 2 from the 3s and 3 from the 3p

Lets take the ionic formula for Calcium Chloride is #CaCl_2#

Calcium is an Alkaline Earth Metal in the second column of the periodic table. This means that calcium #s^2# has 2 valence electrons it readily gives away in order to seek the stability of the octet. This makes calcium a Ca+2 cation.

Chlorine is a Halogen in the 17th column or #s^2p^5# group.
Chlorine has 7 valence electrons. It needs one electron to make it stable at 8 electrons in its valence shells. This makes chlorine a #Cl^(−1)# anion.

Ionic bonds form when the charges between the metal cation and non-metal anion are equal and opposite. This means that two #Cl^(−1)# anions will balance with one #Ca^(+2)# cation.

This makes the formula for calcium chloride, #CaCl_2#.

For the example Aluminum Oxide #Al_2O_3#

Aluminum #s^2p^1# has 3 valence electrons and an oxidation state of +3 or #Al^(+3)#
Oxygen #s^2p^4# has 6 valence electrons and an oxidation state of -2 or #O^(−2)#

The common multiple of 2 and 3 is 6.
We will need 2 aluminum atoms to get a +6 charge and 3 oxygen atoms to get a -6 charge. When the charges are equal and opposite the atoms will bond as #Al_2O_3#.

In molecular (covalent) compounds these same valence electrons are shared by atoms in order to satisfy the rule of octet.

I hope this is helpful.