# Magnesium has atomic number 12. An atom of magnesium has two electrons in its outermost shell. Describe the arrangement of electrons in a magnesium atom and explain how the atomic number relates to the number of electrons in a neutral magnesium atom.

> Pearson Edexcel International GCSE Chemistry (4CH1) — 1.2 Atoms · Describe · 4 marks

> Magnesium is a metal in Period 3 of the periodic table. It has atomic number 12 and its most common isotope has a mass number of 24.

## Mark scheme (4 marks)

1. A neutral magnesium atom has 12 electrons (equal to the number of protons / atomic number)
2. Electrons are arranged in shells/energy levels around the nucleus
3. The electron arrangement is 2, 8, 2 (first shell has 2, second shell has 8, third/outermost shell has 2)
4. In a neutral atom the number of electrons equals the number of protons / the atomic number gives the number of protons, which equals the number of electrons in a neutral atom

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel International GCSE Chemistry (4CH1)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/magnesium-has-atomic-number-12-an-072c9f3f) · Published by Druglandscape Ltd.