Parts of the Atom

Learning Objectives

  • The definition of an element with reference to atomic number; mass number; isotopic forms of an element using appropriate notation

Summary Notes

Atoms are made up of the nucleus (which contains positive protons and neutral neutrons) and negative electrons which surround the nucleus in shells.

Elements are made up of one type of atom, they cannot be chemically broken down.

Protons have a plus one charge.

Neutrons have no charge.

Electrons have a negative one charge.

Atomic Number (Z) of an element is equal to the number of protons in the nucleus of an atom of an element.

Mass Number (A) is the total number of protons and neutrons of an element. You can calculate the number of neutrons in an element by subtracting the atomic number from the mass number.

Isotopes of an element are atoms that have the same atomic number (number of protons) but a different mass number (number of neutrons).

The charge of an atom is equal to the protons minus the electrons.

Videos to help build your understanding

What is An Atom?

Atomic and Mass Numbers

History of the Atom

Practice Material

Teacher's Tip:

Make it a habit to think of the mass number and atomic numbers as the larger and smaller number on the atomic symbols respectively. This is because the position of A and Z can sometimes be swapped around depending on the resources that you use.