Question

The total number of valence electrons in $P{{O}_{4}}^{3-}$ion is:
(A) 26
(B) 28
(C) 24
(D) 32

Answer 1

Hint: We know that elements generally lose or gain the minimum number of electrons which are necessary to achieve a full octet and to become a stable configuration. This is done with the help of valence electrons which are the outermost shell electrons associated to that atom. Since these electrons lie in a valence shell, hence they are named as valence electrons. Here we have to tell the total number of valence electrons in $P{{O}_{4}}^{3-}$ ion.

Complete answer:
Let us first discuss the concept of valence electrons in atoms or ions as follows:-
-Valence electrons: These are the electrons that are associated with an atom and can participate in the formation of a chemical bond such as covalent bond where both atoms in the bond contribute valence electrons in order to form a shared pair.
-These electrons are part of most of the chemical reactions as they contain more energy compared to the electrons that are present in inner orbits. Valence electrons can be calculated by counting the outermost electrons of each atom.
-Now let us calculate the total number of valence electrons in $P{{O}_{4}}^{3-}$ ion as follows:-
The atomic number of oxygen is 8 and hence its electronic configuration is: $1{{s}^{2}}2{{s}^{2}}2{{p}^{4}}$. Here the outermost shell is second and the number of electrons in it is six. Therefore the number of valence electrons in an ‘O’ atom is 6.
The atomic number of phosphorus is 15 and hence its electronic configuration is: $1{{s}^{2}}2{{s}^{2}}2{{p}^{6}}3{{s}^{2}}3{{p}^{3}}$. Here the outermost shell is third and the number of electrons in it is five. Therefore the number of valence electrons in ‘P’ atoms is 5.
Total number of valence electron in an ion= {Sum of number of valence electron of each atom in that ion + negative charge – positive charge}
There are 3 negative charges in $P{{O}_{4}}^{3-}$ ion, so total number of valence electrons= 5 + 4(6) + 3 = 32.

Hence the total number of valence electrons in $P{{O}_{4}}^{3-}$ ion is (D) 32.

Note:
-Remember to study and learn the periodic table with atomic number and electronic configuration of each atom as it is helpful in solving these types of questions.
-Also the number of valence electrons plays an important part in valencies and various oxidation states shown by a particular atom.