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Home · IGCSE 0625 · Nuclear physics · Protons, neutrons, electrons · Practice
Core · Practice questions · Protons, neutrons, electrons

Count the particles.

Six original Cambridge-style questions on the subatomic particles and nuclide notation: relative charge and mass, reading the symbol, and counting protons, neutrons and electrons.

Original questions All questions on this page are original work, written in the Cambridge IGCSE style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
What the examiner wants

Read the two numbers correctly.

01
Recall
[3 marks]

State the relative charge of a proton, a neutron and an electron.

  • Proton: charge +1. ✓
  • Neutron: charge 0 (no charge). ✓
  • Electron: charge -1. ✓
02
Recall
[2 marks]

Compare the relative mass of an electron with the relative mass of a proton.

  • A proton has a relative mass of 1. ✓
  • An electron is far lighter, about 1/1840 of a proton, so its mass is almost nothing. ✓
03
Application
[3 marks]

A neutral atom has a nucleon number of 19 and a proton number of 9. State the number of protons, neutrons and electrons it contains.

  • Protons = 9. ✓
  • Neutrons = A - Z = 19 - 9 = 10. ✓
  • Electrons = 9 (neutral atom). ✓
04
Recall
[2 marks]

Define the proton number and the nucleon number of an atom.

  • The proton number is the number of protons in the nucleus. ✓
  • The nucleon number is the total number of protons and neutrons in the nucleus. ✓
05
Application
[2 marks]

Atom X has 8 protons. Atom Y has 9 protons. Explain why X and Y must be different elements.

  • The element is decided by the proton number. ✓
  • X and Y have different proton numbers, so they are different elements. ✓
06
Application
[2 marks]

An atom of nucleon number 7 and proton number 3 loses one electron to become an ion. State the charge of the ion and explain why.

  • The ion has a charge of +1. ✓
  • It now has 3 protons but only 2 electrons, so there is one more positive charge than negative. ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.