Question

The electronic configuration of an element X is 2, 8, 7.

What is its atomic number?

Answer 1

Step-1: Introduction

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

Step-2: To find the atomic number

The elemental classification is based on electronic configuration. The proton count of the element gives the atomic number of that element.

Atomic number of the element = 2+8+7 = 17.

The element with atomic number 17 is Chlorine ($\mathrm{Cl}$).

Final answer

Therefore, the atomic number of the element with configuration 2,8,7 is 17.