Explain why atoms are electrically neutral, and explain what happens to the overall charge of an atom when it loses an electron.

AQA A-Level Physics (7408) — 3.2.1 Particles · Explain · 5 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (5 marks)

An atom contains protons, which carry a positive charge, and electrons, which carry a negative charge.
The number of protons equals the number of electrons in a neutral atom, so the positive and negative charges cancel.
This balance gives the atom an overall charge of zero.
If the atom loses an electron it becomes a positive ion.
Now there are more protons than electrons, so the overall charge is positive.

Examiner tips

Use the terms ‘protons’, ‘electrons’, ‘positive charge’, ‘negative charge’, ‘neutral atom’, ‘ion’
Show the cancellation of charges to explain neutrality
Explain the change in charge when an electron is lost

Common mistakes

Saying the atom becomes neutral after losing an electron
Using ‘negative ion’ instead of ‘positive ion’
Not mentioning the balance of protons and electrons

Mark scheme (5 marks)

An atom contains protons (which are positively charged) and electrons (which are negatively charged)
The number of protons equals the number of electrons in a neutral atom
The positive and negative charges balance/cancel, giving an overall charge of zero
When an atom loses an electron it becomes a (positive) ion
There are now more protons than electrons, so the overall charge is positive

Key terms in this question

electrically neutral · electron · overall charge