Question

What is the atomicity of an element? How is it useful in writing the chemical formula of an element?

Answer 1

Atomicity:

• The number of atoms in a molecule of an element is called its atomicity.
• For example the atomicity of carbon dioxide (${\mathrm{CO}}_2$) is 3, the atomicity of calcium chloride (${\mathrm{CaCl}}_2$) is 3, and the atomicity of sulphuric acid (${\mathrm{H}}_2{\mathrm{SO}}_4$) is 7.
• The chemical formula for an element is represented by the symbol of the element followed by its atomicity in subscript.
• For example the chemical formula of Calcium is (Ca), Magnesium is (Mg), and Silver is (Ag).
• The chemical formula for a compound is represented by the symbol of each element followed by the number of its atoms present in one molecule, written in the subscript.
• When the number of atoms of an element in the molecule is one, the subscript is not written.
• For example the chemical formula of water is (${\mathrm{H}}_2\mathrm{O}$), carbon dioxide (${\mathrm{CO}}_2$ ), and sodium chloride are ($\mathrm{NaCl}$ ).