The Size Of Atoms (AQA GCSE Combined Science: Synergy: Life & Environmental Sciences): Revision Note

Atomic, molecular and nuclear radius

How big is an atom?

• Atoms are extremely small with a radius of about 1 x 10^-10 metres or 0.1 nanometres

• The radius of a small molecule such as methane (CH₄) is about 5 x 10^-10 metres or 0.5 nm

• The central nucleus contains protons and neutrons only, packed close together in a small region of space

• The radius of the nucleus is about 10 000 times smaller than that of the atom, around 1 x 10^-14 m

  • So, it is an extremely small region of space compared to the overall size of the atom

• This means that virtually all of the atom's mass is concentrated inside the nucleus

• Electrons have a much smaller mass than protons and neutrons (1 proton has the same mass of around 1840 electrons) and move in the space outside the nucleus in orbits

Sub-Atomic Particle Mass Comparison Table

The size and scale of an atom

• To put the size of an atom into perspective, if an atom were magnified to the size of a football stadium, then:

  • The nucleus would be the size of a small pea at the centre of the pitch where kick-off takes place

  • The electrons would be orbiting the pea at the outermost seats of the stadium

  • In between the nucleus and the electrons is nothing but empty space

• Another way to think about the size of an atom is to consider that the size of a full stop on a piece of paper is usually 0.003 m = 3 x 10^-3 m

• The width of a hydrogen atom is about 1.06 x 10^-10 m

• This means that you could fit almost 28,301,887 hydrogen atoms across the diameter of a full stop!