Magnesium (Mg) — Atomic Number 12

Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny grey alkaline earth metal. It is essential for life — it is the central atom in chlorophyll. It burns with a brilliant white light. First isolated by Sir Humphry Davy in 1808.

At a Glance

Chemical Properties

Magnesium loses two 3s² electrons to form Mg²⁺ (configuration 2,8, like neon).

Key Reactions

1. Combustion: $2\text{Mg}+{\text{O}}_2\to 2\text{MgO}$ — brilliant white flame (UV radiation — do not look directly)
2. With steam: $\text{Mg}+{\text{H}}_2\text{O}\to \text{MgO}+{\text{H}}_2$ — reacts with hot water/steam
3. With acid: $\text{Mg}+2\text{HCl}\to {\text{MgCl}}_2+{\text{H}}_2$

Compounds & Uses

• Lightweight alloys — aircraft, cars, laptops
• Flares and fireworks — brilliant white light
• Chlorophyll — magnesium enables photosynthesis

IGCSE Essentials

1. Burns with brilliant white light
2. Forms Mg²⁺ (loses 2 electrons)
3. Reacts with steam but only slowly with cold water
4. Group 2 trend: Be < Mg < Ca < Sr < Ba (reactivity increases down)

Sources

• Magnesium — Wikipedia
• Magnesium — Ptable.com
• Magnesium — RSC Periodic Table