Question

Silicon (atomic no. 14) and phosphorous (atomic no. 15) belong to same period of the periodic table.

(a) State the electronic configuration of:

1. Silicon
2. Phosphorous

(b) Name the period in which above elements occur

Answer 1

(a) Electronic configuration: It is the distribution of electrons in the various shells around the nucleus of an atom.
(i) Atomic number of Silicon $\left(\mathrm{Si}\right)$= 14

• As atomic number= Number of protons and
• Number of protons= Number of electrons for a neutral atom
• Electronic configuration of Silicon= 2, 8, 4 (K, L, M)

(ii) Atomic number of Phosphorous $\left(\mathrm{P}\right)$= 15

• Electronic configuration of Phosphorous= 2, 8, 5 (K, L, M)

(b) These elements occur in 3^rd period.

• The number of shells present in the atom of an element indicate the period number.
• Example: Silicon and Phosphorous accommodate their electrons in three shells i.e. K, L, M. Therefore their period number is 3.
• This can also be confirmed from the periodic table given below.