Question

A neutral atom has the following electronic configuration: 1s² 2s² 2p⁶ 3s²3p⁵

How many protons are in the atomic nucleus and to which group of the periodic table does this element belong?

Answer 1

1s2 2s2 2p6 3s2 3p5

Just add the number of electrons in each sub shells, that is =2+2+6+2+5 = 17, means atomic number of given element is 17, or ₁₇Cl. Therefore the number of protons = 17

Reason: the number of protons and electrons are equal in a neutral atom.

Group?

It belongs to 17 th group or halogens family. Another way of finding group number of elements in p-block is, add 10 with the number of electrons in valance shell, 3s² 3p⁵ . So group number = 10+2+5 =17

₁₇Cl = 1s² 2s² 2p⁶ 3s² 3p⁵