Atomic Structure

Describing Nucleus

• Atom = nucleus (proton and neutron) and electrons

• Nucleus = protons and neutrons at the centre of the atom

​Proton Number (Z)

• The number of protons in an atom is called its proton number (it can also be called the atomic number)

Nucleon Number (Z)

• The total number of particles in the nucleus of an atom is called its nucleon number (or mass number)

• The mass number is the number of protons and neutrons in the atom

• The number of neutrons can be found by subtracting the atomic number from the mass number

​Number of Neutrons = Nucleon Number - Proton Number

Example

​Practice