Matter is composed of tiny particles, called molecules, which are continuously in motion. These molecules themselves comprise of groups of atoms.
Most of the atom is empty space. At its centre, it has a small, dense and positively charged nucleus of squashed protons and neutrons, surrounded by a cloud of negatively charged electrons.
Atom is the smallest unit of matter that has the characteristic properties of a chemical element.
- As such, the atom is the basic building block of chemistry.