Atoms & structure
Atom — পরমাণু
Quick answer
The atom is the smallest particle of an element that still shows that element's chemical identity.
Definition
An atom is the basic unit of matter: a tiny nucleus of protons and neutrons surrounded by electrons in shells. The number of protons, the atomic number, fixes which element the atom belongs to, while the arrangement of electrons decides how it bonds and reacts. Atoms are about a tenth of a nanometre across, so a single full stop on this page holds more atoms than there are people on Earth.
For example
A gold ring is a vast crowd of gold atoms, all with 79 protons each; a drop of water is an even vaster crowd of oxygen and hydrogen atoms joined in pairs.