# Describe how the properties of elements change across Period 3 of the periodic table, from sodium to argon. Include at least one physical property and one chemical property in your answer.

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

> Period 3 contains the elements sodium (Na), magnesium (Mg), aluminium (Al), silicon (Si), phosphorus (P), sulfur (S), chlorine (Cl), and argon (Ar).

## Mark scheme (5 marks)

1. Metallic character decreases across Period 3 (from metals on the left to non-metals on the right) / sodium, magnesium and aluminium are metals; phosphorus, sulfur and chlorine are non-metals
2. Melting point generally increases from sodium to silicon (silicon has the highest melting point) then decreases from silicon to argon
3. Argon (noble gas) has very low / negligible melting and boiling points and exists as a monatomic gas at room temperature
4. Reactivity of metals decreases from sodium to aluminium (sodium is most reactive metal in the period) / sodium reacts vigorously with water but aluminium does not react noticeably with water
5. Reactivity of non-metals increases from sulfur to chlorine across the period / chlorine is more reactive than sulfur or phosphorus / non-metal reactivity increases going right (towards Group 7)

## Key terms

- [Period 3](https://www.gradenine.co.uk/glossary/period-3)

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](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/describe-how-the-properties-of-elements-0fae865d) · Published by Druglandscape Ltd.