Question

How many elements are there in period 1?

Answer 1

The period in the periodic table:

• The elements in the horizontal rows of a periodic table represent periods.
• The first period elements are the elements in the first row of the periodic table.

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

Let 'p' be the period number, and

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

Since the period number is 1, it is odd.

Therefore, the number of elements in period 1 will be

$\frac{{\left(1+1\right)}^2}{2}=\frac{4}{2}=2$

Hence, there are 2 elements in period 1 of the periodic table, Hydrogen $\left(\mathrm{H}\right)$ and Helium $\left(\mathrm{He}\right)$.