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 is made up of two different types of particles:

  • Protons
  • Neutrons

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.

  • In fact, the radius of a nucleus can be 10,000 times smaller than the diameter of the entire atom, with most of the atom being 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 proteins 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.

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

  • The first atom has 8 protons and 8 electrons, so it has a neutral charge of 0.
  • The second atom has 8 protons and 9 electrons, so it has a negative charge of -1.
  • The third atom has 8 protons and 7 electrons, so it has a positive charge of +1.