The name proton was given to these particles.

The idea

After the discovery of the electron, scientists needed to explain how an atom could be neutral overall. Rutherford's group found that alpha particles were occasionally deflected strongly by a tiny, dense, positively charged region at the centre of the atom. The positive particles in that nucleus were later named protons. The name comes from the Greek word for 'first', because protons were regarded as fundamental building blocks of matter. In the modern model, each proton carries a relative charge of 1⁺ and a relative mass of 1, and the number of protons in the nucleus is the atomic number, which identifies the element.

For example: Every carbon atom has six protons, so its atomic number is 6.

What earns the marks

• State that protons are the positively charged particles found in the nucleus of an atom.
• Give the relative charge of a proton as 1⁺ and its relative mass as 1.
• Explain that the name proton was given to the positive particles identified in the nucleus after the nuclear model was proposed.
• Link the number of protons in the nucleus to the atomic number and hence to the identity of the element.
• Recognise that the positive charge of protons balances the negative charge of electrons in a neutral atom.

Common mistakes and how to put them right

• Saying that protons orbit the nucleus like electrons.

  Put it right by stating that protons are inside the nucleus.

• Describing a proton as having no charge or a negative charge.

  Put it right by stating that a proton has a relative charge of 1⁺.

• Confusing atomic number with mass number.

  Put it right by stating that atomic number equals the number of protons, while mass number equals protons plus neutrons.

Exam tips

• Use the wording 'relative charge' and 'relative mass' when comparing subatomic particles, because these are the quantities used in atomic models.
• When asked to identify an element from data, count the protons rather than the electrons, since the proton number defines the element.
• Sketch a simple nuclear model with a tiny central nucleus and label the proton position clearly to support a written answer.