Question

Define atomicity.

Answer 1

Hint: Atomicity is based on the number of atoms present in a molecule. It depends on the number of atoms which are bonded together. They are of four types depending on the value of atomicity.

Complete step by step solution:
Matter is anything that takes up space and has mass. Atoms are the fundamental unit of matter. Molecules or compounds are made up of these atoms. Elements are a part of an atom. Central part of the atom is termed as the nucleus. Nucleus contains protons and neutrons. Protons are the positive charged atomic particles and the neutrons are the uncharged or neutral atomic particles. Electrons orbit around the nucleus. They are negatively charged. Protons attract electrons.
There are different types of atomic theories developed by different people. They are Dalton’s atomic theory, Rutherford’s atomic model, Bohr model of atom, etc.
Atomicity is the number of atoms present in a molecule of an element or compound. E.g. The atomicity of hydrogen molecules is 2. Hydrogen molecule is represented as ${\text{H}}_2$
Atomicity of oxygen molecules is 2. It is represented as ${\text{O}}_2$
Atomicity of ozone molecules is 3. It comprises 3 oxygen atoms. It is represented as ${\text{O}}_3$.
Molecules are divided into four types depending on the atomicity-monoatomic, diatomic, triatomic and polyatomic.
Monoatomic molecules are those having atomicity equal to 1 or it consists of only one atom.
Diatomic molecules are those having atomicity equal to 2 or it consists of two atoms.
Triatomic molecules have atomicity equal to 3
Polyatomic molecules have atomicity greater than 3.
Additional information:
Some examples of monatomic molecules are Helium, Neon or all the noble gases.
Diatomic- ${\text{O}}_2,{\text{H}}_2,{\text{N}}_2$etc.
Triatomic-${\text{O}}_3$
Polyatomic- ${\text{P}}_4,{\text{S}}_8$

Note: Atomicity is based on the number of atoms and valency is based on the number of electrons in the outermost shell. Valency tells about the ability to combine with other atoms. Atomicity is also based on the atoms bound to each other.