Atomic theory

Structure of the atom

Everything in the world is made up of atoms. The structure of the atom is what gives an element its chemical and physical properties.

Atoms are made up of three smaller particles:


Negatively charged particles that spin around the positive centre of the atom in circles called energy levels. Their mass is so small it is nearly zero.


Positively charged particles that are contained in the nucleus of the atom (the centre) they have a mass of 1 amu (atomic mass unit).


Particles with no charge that are also contained in the nucleus of the atom. They also have a mass of 1 amu.

Electrons orbit a central nucleus of protons and neutrons.Electrons orbit a central nucleus of protons and neutrons

The nucleus has an overall positive charge as it contains the protons.

ElectronApprox 0-1Energy level
Proton1 amu+1Nucleus
Neutron1 amu0Nucleus

Every atom has no overall charge (neutral). While atoms do contain charged particles, they have the same number of positive protons as negative electrons. These opposite charges cancel each other out making the atom neutral.