# Phosphorus has atomic number 15 and mass number 31. State the number of protons, neutrons and electrons in one atom of phosphorus, and state in which electron shells these electrons are arranged.

> Pearson Edexcel International GCSE Chemistry (4CH1) — 1.3 Atomic structure · State · 4 marks

## Mark scheme (4 marks)

1. Number of protons = 15
2. Number of neutrons = 16
3. Number of electrons = 15
4. Correct electron shell arrangement: 2, 8, 5

## Key terms

- [atomic number](https://www.gradenine.co.uk/glossary/atomic-number)
- [mass number](https://www.gradenine.co.uk/glossary/mass-number)
- [proton](https://www.gradenine.co.uk/glossary/proton)
- [neutron](https://www.gradenine.co.uk/glossary/neutron)
- [electron](https://www.gradenine.co.uk/glossary/electron)
- [electron shell](https://www.gradenine.co.uk/glossary/electron-shell)

## Related

- [Revision notes for Pearson Edexcel International GCSE Chemistry (4CH1)](https://www.gradenine.co.uk/learn)
- [How to answer "State" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/phosphorus-has-atomic-number-15-and-b90354bd) · Published by Druglandscape Ltd.