Question

What is the valency of phosphorus in $P{H}_{3}$?
A.-1
B.+2
C.+3
D.-4

Answer 1

Hint: Valency of an atom is defined as the number of hydrogen atoms that can combine with or replace from one atom of element. Simply it is the number of electrons with which an atom can bond.

Complete step by step answer:
Valency or valence of an element can be defined as the measure of its combining power with other atoms in order to form compounds or molecules. It is related to the number of electrons present in the outermost shell of an atom.

- If the number of electrons in the outermost shell of an element is one to four, then the element is said to have positive valency and it is equal to the no. of electrons present in the outermost shell.

- And if the number of electrons in the outermost shell of an element is greater than 4, then the element is said to have a negative valency and it is calculated by subtracting 8 from it.

-The elements of the same group are said to have the same valency. For a molecule which is in the stable state, is known to have the valency 0.

- Let us now consider the case of $P{H}_{3}$. It contains phosphorus and hydrogen as its constituent elements. The number of valence electrons or the number of electrons in the outermost shell of phosphorus is 3.

- Thus, one atom of phosphorus is capable of combining with three atoms of hydrogen in order to form phosphine $(P{H}_{3})$.

Therefore, the valency of phosphorus in $P{H}_{3}$ is +3. Hence, the correct answer is option (C).

Note: Valency and oxidation state might seem the same but they are not. Valency is the combining capacity of an electron whereas oxidation state is defined as the total no. of electrons an element can gain or lose in order to form a chemical bond.