Question

Why first period in the morden periodic
table contain only two elements​

Answer 1

Answer:

There are only two elements in the first period: hydrogen and helium. ... This is because in quantum physics, this period fills up the 1s orbital. Period 1 elements follows the duet rule, they only need two electrons to complete their valence shell. These elements can only hold two electrons, both in the 1s orbital.

Explanation:

I hope it will help you have a nice day ahead

Answer 2

because the inventor of the periodic table made it easy to learn by distributing the elements in ascending order.