Atomicity

Atomicity

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.

ACTIVITY

Write down atomicity of the following elements and compounds.

Elements                 Atomicity

Cl                                       2

Na                                       1

K                                         1

Ca                                        1

Compounds              Atomicity

H₂O                                       3

Nacl                                       2  

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.