Question

Period 5 of the periodic table contains _____elements.

Answer 1

The number of elements in a period can be determined as:

Let 'p' be the period number, and

1. If p is even, then the number of elements is: $\frac{{\left(p+2\right)}^2}{2}$
2. If p is odd, then the number of elements is: $\frac{{\left(p+1\right)}^2}{2}$

Since the period number is 5, it is odd.

Therefore, the number of elements in period 5 will be

$\frac{{\left(5+1\right)}^2}{2}=\frac{36}{2}=18$

Hence, period 5 of the periodic table contains 18 elements.