About The Unit ^🔗

• Chemical Reactions
• External
• 4 Credits

Ngā Whāinga Ako ^🔗

• Review the structure of the atom

Copy this diagram into your book.

Overview ^🔗

An atom is made up of two distinct parts. The nucleus and electrons.

• The nucleus is the centre of the atom (B).
• The electrons (C) move around the nucleus in a shell (A)
• If one orbit is a shell, all the shells together are called the electron shells (F)
• The nucleus holds the vast majority of the mass and is made of two particles
• The proton (D) and the neutron (E)

Atomic Number

The number of protons inside the nucleus.

Mass Number

The number of protons + neutrons inside the nucleus.

NB: In a neutral atom, the number of protons is equal to the number of electrons. Why?