Atoms

The Model of an Atom

• Atoms are made up of smaller particles called subatomic particles.

• The protons and neutrons are called the nucleons which are found in the nucleus.
• The nucleus is surrounded by a ‘cloud’ of electrons.
• The electrons are arranged in shells.
• An atom is electrically neutral when the number of protons = number of electrons.

Subatomic particle	Symbol	Relative mass	Charge
Proton	p	1	1+
Neutron	n	1	0
Electron	e⁻	1/1840	1-

Each element has its own structure of atom

Proton Number (atomic number)

• Number of protons in an atom
• Number of electrons in an electrically neutral atom

Nucleon Number (atomic mass)

• number of protons + number of neutrons in the nucleus of an atom