Explain atoms and molecules?

An atom is the smallest constituent unit of ordinary matter that constitutes a chemical element. Every solid, liquid, gas, and plasma is composed of neutral or ionized atoms. Atoms are extremely small, typically around 100 picometers across.

Atoms consist of three basic particles: protons, electrons, and neutrons. The nucleus (centre) of the atom contains the protons (positively charged) and the neutrons (no charge). The outermost regions of the atom are called shells and contain the electrons (negatively charged).

A molecule is made up of two or more atoms of the same kind or of different kinds chemically combined together. 

• Molecules exist in both elements and compounds. 

• Molecules in elements consist of a fixed number of one kind of atom only.

Examples: Molecules of the element are O2, Na₂, molecules of a compound are H₂O, NaCl.