# Explain why elements in Period 3 show a trend from metallic to non-metallic character as you move from left to right across the period.

> AQA A-Level Chemistry (7405) — 3.2.1 Periodicity · Explain · 5 marks

> Period 3 of the periodic table contains elements ranging from sodium (Na) to argon (Ar). Chemists observe that the physical and chemical properties of these elements change systematically across the period.

## Mark scheme (5 marks)

1. The number of protons (atomic number / nuclear charge) increases across the period
2. The number of electrons in the outer shell increases from 1 to 8 across the period
3. Metals on the left lose electrons easily to form positive ions / have low ionisation energies
4. Non-metals on the right tend to gain electrons or share electrons / have nearly full outer shells
5. The same (third) electron shell is used across the whole period, so the increasing nuclear charge pulls outer electrons more strongly to the right, making it harder to lose electrons

## Key terms

- [period](https://www.gradenine.co.uk/glossary/period)
- [metallic character](https://www.gradenine.co.uk/glossary/metallic-character)
- [non-metallic character](https://www.gradenine.co.uk/glossary/non-metallic-character)

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](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/explain-why-elements-in-period-3-77aacf14) · Published by Druglandscape Ltd.