Atomic Structure and Ions

Everything around us is made up of tiny particles called atoms. Each atom is made up of smaller particles called subatomic particles. The basic structure of an atom is a central nucleus surrounded by electrons, which orbit the nucleus in shells.

Subatomic particles

The nucleus contains two types of subatomic particles:

  • Protons
  • Neutrons
A diagram of a labelled atom showing the protons and neutrons in the nucleus and the electrons on the shells.

Protons are positively charged particles, while neutrons are neutral particles that do not carry any charge. The nucleus of an atom is incredibly dense and much smaller in size compared to the overall size of the atom.

  • n fact, the radius of a nucleus is about 10,000 times smaller than the radius of the entire atom, making most of the atom’s volume empty space.

The masses of subatomic particles are extremely small. So instead of measuring their absolute masses, scientists use relative masses. This means that the masses of subatomic particles are compared to a standard unit. By using relative masses, scientists can compare the masses of different particles.

The table below shows the relative mass and charge of each subatomic particle.

Subatomic particleRelative massRelative charge
ElectronVery small-1

You can remember that protons are positive and neutrons are neutral.

Most of an atom is empty space, but the nucleus contains protons and neutrons, so most of the mass is concentrated in the nucleus. The atom in the diagram above has 3 positively charged protons and 3 negatively charged electrons. So, the overall charge of the atom is neutral.

The Formation of Ions

Atoms can lose or gain electrons to form ions.

A diagram showing a neutral atom losing an electron to become a positive cation and an alternative path where it gains an electron to become a negative anion.

For example, let’s look at the diagram below.

A diagram depicting 3 atoms. One with a neutral charge as there are an equal number of protons and electrons, one with a -1 charge as there is one more electron than protons and one with a +1 charge as there is one more proton than electrons.

  • The first atom has 8 protons and 8 electrons, giving it a neutral charge.
  • The second atom has 8 protons and 9 electrons, giving it a charge of -1.
  • The third atom has 8 protons and 7 electrons, giving it a charge of +1.

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