Question

This question is related to Period 3 of the modern periodic table.

How many elements are there in this period?

Answer 1

The period in a Periodic table:

1. The elements in the horizontal rows of a periodic table represent periods.
2. The 3rd-period elements are the elements in the 3rd row of the periodic table.

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

Let 'p' be the period number, and

1. If p is even: $\raisebox{1ex}{${\left(p+2\right)}^2$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$
2. If p is odd: $\raisebox{1ex}{${\left(p+1\right)}^2$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$

Since the period number is 3, it is odd.

Therefore, number of elements in period 3 will be

$$\begin{gathered} \raisebox{1ex}{${\left(3+1\right)}^2$}\!\left/ \!\raisebox{-1ex}{$2$}\right.=16/2 \\ =8 \end{gathered}$$

Hence, there are 8 elements in period 3 of the modern periodic table.