# Magnesium has atomic number 12. Describe the structure of a magnesium atom, including the number and location of each type of subatomic particle and the arrangement of its electrons in shells.

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

> Magnesium is a metal in Group 2 of the periodic table. It has atomic number 12 and mass number 24.

## Mark scheme (4 marks)

1. The nucleus contains 12 protons (and 12 neutrons for mass number 24)
2. The atom has 12 electrons orbiting the nucleus
3. Electrons are arranged in shells/energy levels: 2 electrons in the first shell and 8 in the second shell
4. 2 electrons in the third (outermost) shell

## 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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