# Magnesium oxide is an ionic compound formed when magnesium reacts with oxygen. Explain how magnesium oxide is formed from its elements, including why the ions formed have the charges they do, and why the overall compound has no overall charge.

> Edexcel A-Level Chemistry (9CH0) — 2.1 Ionic bonding · Explain · 5 marks

> Magnesium is in Group 2 of the periodic table. Oxygen is in Group 6.

## Mark scheme (5 marks)

1. Magnesium atom loses 2 electrons to form a Mg²⁺ ion
2. Oxygen atom gains 2 electrons to form an O²⁻ ion
3. Ions achieve a full outer electron shell / stable noble gas electron configuration
4. The charges on the ions are linked to their group number — Group 2 element loses 2 electrons giving a 2+ charge; Group 6 element gains 2 electrons giving a 2− charge
5. The compound has no overall charge because the 2+ charge on Mg²⁺ and the 2− charge on O²⁻ cancel out / balance each other in a 1:1 ratio

## Key terms

- [ionic compound](https://www.gradenine.co.uk/glossary/ionic-compound)
- [ion](https://www.gradenine.co.uk/glossary/ion)
- [overall charge](https://www.gradenine.co.uk/glossary/overall-charge)

## Related

- [Revision notes for Edexcel A-Level Chemistry (9CH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" 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/magnesium-oxide-is-an-ionic-compound-5d941592) · Published by Druglandscape Ltd.