Question

What is the valency of the element with atomic number $35$ and$15$?

Answer 1

As we know that in chemistry, periodic tables play a vital role. In the periodic table there are totally $118$ elements. In the periodic table there are totally $18$ columns and $7$ rows. The columns are called groups. Hence, $18$ groups in the periodic table. The rows are called periods. Hence, totally $7$ period in the table. The valency is nothing of the number of electrons that donate or accept the atom to attain the stable electronic configuration.

Complete answer:
We also need to know that the valency of the atom is nothing but the number of electrons gain or loss to attain the stable electronic configuration in the molecule.
The general electronic configuration of the element with atomic number $36$ is${\text{1}}{{\text{s}}^{\text{2}}}{\text{,2}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{p}}^{\text{6}}}{\text{3}}{{\text{s}}^{\text{2}}}{\text{3}}{{\text{p}}^{\text{6}}}{\text{3}}{{\text{d}}^{10}}{\text{4}}{{\text{s}}^{\text{2}}}{\text{4}}{{\text{p}}^6}$.
The general electronic configuration of the element with atomic number $35$ is${\text{1}}{{\text{s}}^{\text{2}}}{\text{,2}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{p}}^{\text{6}}}{\text{3}}{{\text{s}}^{\text{2}}}{\text{3}}{{\text{p}}^{\text{6}}}{\text{3}}{{\text{d}}^{10}}{\text{4}}{{\text{s}}^{\text{2}}}{\text{4}}{{\text{p}}^5}$.
The atom having atomic number of $36$ is stable, for this stable electronic configuration of the element with atomic number $35$ is accept the one electron. Hence the valency of the element with atomic number $35$ is one.
The general electronic configuration of the element with atomic number $18$ is ${\text{1}}{{\text{s}}^{\text{2}}}{\text{,2}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{p}}^{\text{6}}}{\text{3}}{{\text{s}}^{\text{2}}}{\text{3}}{{\text{p}}^3}$.
The general electronic configuration of the element with atomic number $15$ is ${\text{1}}{{\text{s}}^{\text{2}}}{\text{,2}}{{\text{s}}^{\text{2}}}{\text{2}}{{\text{p}}^{\text{6}}}{\text{3}}{{\text{s}}^{\text{2}}}{\text{3}}{{\text{p}}^{\text{6}}}$.
The atom having atomic number of $18$ is stable, for this stable electronic configuration of the element with atomic number $15$ accepts the three electrons. Hence the valency of the element with atomic number $15$ is three.

Note:
We need to know that the atomic number of the element is nothing but the number of electrons or number of protons. The mass number of the atom is nothing but the sum of the number of protons and the number of neutrons. The atomic number of the atom is equal to the number of protons or the number of electrons. In every atom the number of protons and the number of electrons are equal. The stable electronic configuration in the second period is $10$. The stable electronic configuration in the third period is $18$.