Question

Why is the second ionisation energy of silicon lower than Aluminium?

Answer 1

Answer:

Stability of valence shell electronic configuration.

Explanation:

Silicon belongs to group 4A and has valence shell electronic configuration 3s² 3p² while Aluminium belongs to 3A with valence shell configuration 3s² 3p¹. Removal of first electron changes configuration of Silicon to 3s²3p¹ (Si+1) and Aluminium changes to 3s² (Al+1). Complete s orbital of Al+1 ion makes it difficult to remove the second electron and Si+1 ion has less than half filled p orbital (3p¹) which makes it easier to remove the second electron. Thus, second ionisation energy of Silicon is lower than Aluminum.

Answer 2

Reason for lower ionisation energy of silicon is as follows -

• The electron configuration of silicon is [Ne] 3s² 3p².
• The electronic configuration of aluminium is [Ne] 3s² 3p¹.
• After removal of first electron, silicon has outermost electron at 3p¹ and aluminium has outermost electron at 3s².
• Here as can be seen, s orbital is completely filled while p orbital is neither half nor completely filled.
• This is the reason, it is easier to remove second electron from silicon than aluminium and thus it has lower second ionisation energy.