Question

What is meant by atomicity?

Answer 1

Hint:Atomicity determines the total no. of atoms present in the molecule or we can say that the no. of atoms combining to form a molecule of an element. It can be calculated by taking the ratio of molecular mass and atomic mass of a particular element.

Complete step by step answer:
Total no. of atoms in the molecule of an element determines its atomicity. For example- an oxygen molecule contains two atoms of oxygen to form ${{O}_{2}} $molecule, so its atomicity is 2. We can find its atomicity by taking the ratio of molecular and atomic masses. The atomic mass of oxygen is 16u and molecular mass of oxygen is 32u. Taking the ratio of both we get, Atomicity of oxygen = $\dfrac{32}{16}$ = 2.
Molecules are classified into different types on the basis of atomicity as-
Monoatomic- molecule composing one single atom, helium is monatomic in nature.
Diatomic- molecule containing two atoms, oxygen is diatomic in nature as it exists as ${{O}_{2}} $molecule.
Triatomic- molecule compositing three atoms, ${{O}_{3}} $ exists as an ozone molecule.
Polyatomic- which contains more than 3 atoms, ex- ${{S}_{8}} $
Atomicity for water can be determined as it contains two atoms of hydrogen and one atom of oxygen so its atomicity is 3.

Note:
Atomicity should not be confused with valency. Valency determines the maximum no. of electrons that an atom can gain or lose to become stable while atomicity determines the no. of atoms present in a molecule of an element. Valency does not depend upon the no. of atoms, it is determined through electronic configuration of the atom. Atom with unity valency is known as mono-valence whereas a molecule containing one atom is known as monatomic.