Skip to content
Grade 9 Intermediate About 20 min Version 1 Awaiting review Premium

Build an atom

An atom has a tiny nucleus made of protons (positive) and neutrons (no charge), surrounded by electrons (negative) in shells. The number of protons is the atomic number, and it decides which element the atom is. Protons + neutrons = mass number. In a neutral atom there are as many electrons as protons. Electrons fill shells from the inside: up to 2 in the first, 8 in the second and 8 in the third. An atom that gains or loses electrons becomes a charged ion. Atoms of the same element with different numbers of neutrons are isotopes.

What you will learn

  • Describe the structure of an atom.
  • Work out the atomic number, mass number and electron arrangement.
  • Explain what ions and isotopes are.

Before you start

  • Know that elements are made of atoms.

Materials

  • Coloured beads or a periodic table (for a real model)

Equipment

  • None

Procedure

  1. Build a hydrogen atom: 1 proton, 0 neutrons, 1 electron. Record it.
  2. Build carbon-12: 6 protons, 6 neutrons, 6 electrons. Record it.
  3. Build a sodium ion: 11 protons, 12 neutrons, 10 electrons.
  4. Build a chloride ion: 17 protons, 18 neutrons, 18 electrons.
  5. Build carbon-14: 6 protons, 8 neutrons, 6 electrons.

How this simulation is simplified

  • Electrons fill shells of 2, 8, 8 and then the fourth shell, which is right for the first 20 elements.
  • A nucleus is shown as unstable if it has far too few or far too many neutrons for its protons (a rough guide only).