In chemistry we usually understand atomicity to imply the total number of atoms present in one molecule of an element, compound or a substance.
Let we see how to calculate the atomicity of elements. For example, Oxygen exists as a diatomic molecule which means that a molecule of oxygen contains two atoms hence its atomicity is 2.
O+O → O2
(Oxygen atom + Oxygen atom) → Oxygen Molecule
Similarly a phosphorus (P4) molecule contains 4 atoms; a sulphur (S8) molecule contains 8 sulphur atoms. Hence their atomicity is 4 and 8 respectively.
For molecule containing more than one types of atoms, simply count the number of each atom and that would be its atomicity. For example, a molecule of sulphuric acid (H2SO4) consists of 2 hydrogen atom, 1 sulphur atom and 4 oxygen atoms. Hence e its atomicity is 2+1+4=7.
One molecule of water (H2O) contains two atoms of hydrogen and one atom of oxygen, the atomicity of water is three.
Elements in human Body
Nearly 99% of the mass of our human body consists of just 6 chemical elements: oxygen, carbon, hydrogen, nitrogen, calcium, andphosphorus. Another 5 elements make up most of the least percentage point: potassium, sulphur, sodium, chlorine, and magnesium.
Write down atomicity of the following elements and compounds.
Elements in air
Air is a mixture of gases. The molecules of two different elements, nitrogen and oxygen, make up about 99% of the air. The rest includes small amounts of argon and carbon dioxide. (Other gases such as neon, helium, and methane are present in trace amounts.) Oxygen is the life-giving element in the air.