Atom And Molecule


An atom is the smallest unit into which matter can be divided without the release of electrically charged particles.

It also is the smallest unit of matter that has the characteristic properties of a chemical element.

The atom is the basic building block of all matter.

Atoms are very small, they are smaller than anything that we can imagine or compare with.

More than millions of atoms when stacked would make a layer barely as thick as a sheet of paper.

Most of the atom is empty space.

The rest consists of a positively charged nucleus of protons and neutrons surrounded by a cloud of negatively charged electrons.


Atomic mass

Atomic mass is the average mass of atoms of an element, calculated using the relative abundance of isotopes in a naturally-occurring element.

Atomic mass indicates the size of an atom.

Although the mass is the sum of all the protons, neutrons and electrons in an atom.


A molecule is in general a group of two or more atoms that are chemically bonded together, that is tightly held together by attractive forces.

A molecule can be defined as the smallest particle of an element or a compound that is capable of an independent existence and shows all the properties of that substance.

Atoms of the same element or of different elements can join together to form molecules.



Compounds composed of metals and non-metals contains charged species. The charged species are known as Ions.

An ion is a charged particle and can be negatively or positively charged.

Negatively charged ion is called an ‘anion’ and the positively charged ion, a ‘cation’.

A group of atoms carrying a charge is known as a polyatomic ion.