Question

Write the electronic configuration of each one of Li (3), Na (11) and K (19) and answer the following question:

What is the period of Na in the periodic table.

Answer 1

Step-1: Introduction

The elements in periodic table are placed in periods and groups. Periods are horizontal rows that has increasing atomic numbers. Groups are vertical columns. There are 7 periods and 18 groups in periodic table.

Step-2: Electronic configuration

Atomic numbers of Lithium ($\mathrm{Li}$), Sodium ($\mathrm{Na}$) and Potassium ($\mathrm{K}$) are 3, 11 and 19 respectively.

Electronic configuration of Lithium = (2, 1).

Electronic configuration of Sodium = (2, 8, 1).

Electronic configuration of Potassium = (2, 8, 8, 1).

Step-3: Period of Sodium

Sodium has 2 electrons in K-shell, 8 electrons in L-shell and 1 electron in M-shell. So, it has 3 shells.

Number of shells = Number of period

So, period number is 3.

Therefore, the period number of Sodium in the periodic table is 3.