Chapter 8, Problem 2STP

Interpretation Introduction

Interpretation: The number of valence electrons in a molecule of phosphoric acid needs to be determined.

Concept Introduction: The number of valence electrons in an atom is equal to the number of electrons present in the valence shell. For a molecule, the number of valence electrons can be calculated by taking the sum of valence electrons of each atom in the molecule.

Answer to Problem 2STP

Option (D)

Explanation of Solution

Reason for correct options:

The given molecule is phosphoric acid, ${\text{H}}_{\text{3}}{\text{PO}}_{\text{4}}$ . The atoms present in the molecule are H, P, and O. Here, the number of valence electrons in a hydrogen atom is 1, the number of valence electrons in a phosphorus atom is 5, and that in an oxygen atom is 6. Since, there are 3 hydrogen atoms, 1 phosphorus atom, and 4 oxygen atoms, the total number of valence electrons can be calculated as follows:

  $\begin{array}{l}N=3\left(1\right)+5+4\left(6\right)\\ =3+5+24\\ =32\end{array}$

Thus, the total number of valence electrons in ${\text{H}}_{\text{3}}{\text{PO}}_{\text{4}}$ molecule is 32.

The correct option is (D).

Conclusion

Reason for incorrect options:

The total number of valence electrons in a molecule is the sum of valence electrons of each atom present in the molecule. Since, after calculation, the total number of valence electrons comes out to be 32, options (A), (B), and (C) are incorrect options.