Sodium (Na) — Atomic Number 11

Sodium is a chemical element with the symbol Na (from Latin natrium) and atomic number 11. It is a soft, silvery-white alkali metal that is highly reactive — it must be stored under oil. It is the sixth most abundant element in Earth’s crust. The pure metal was first isolated by Sir Humphry Davy in 1807 by electrolysis of molten caustic soda.

At a Glance

Chemical Properties

Sodium readily loses its single 3s¹ electron to form Na⁺ (configuration 2,8, like neon). It is more reactive than lithium but less reactive than potassium.

Key Reactions

1. With water: $2\text{Na}+2{\text{H}}_2\text{O}\to 2\text{NaOH}+{\text{H}}_2$ — fizzes, melts into a silvery ball, darts around, may ignite with a yellow flame
2. With oxygen: $4\text{Na}+{\text{O}}_2\to 2{\text{Na}}_2\text{O}$
3. With chlorine: $2\text{Na}+{\text{Cl}}_2\to 2\text{NaCl}$ (vigorous, yellow flame, white smoke)

Characteristic Test

Flame test: Intense golden yellow

Extraction

Extracted by the electrolysis of molten sodium chloride (Downs Process). NaCl is mixed with CaCl₂ to lower the melting point. Sodium forms at the cathode, chlorine at the anode.

Compounds & Uses

• Sodium vapour lamps — the yellow glow of street lights
• Coolant in some nuclear reactors (liquid sodium)

IGCSE Essentials

1. Flame test: bright yellow — classic exam identification
2. Stored under oil — reacts violently with water
3. Reactivity: Li < Na < K (increases down Group 1)
4. Conducts electricity when molten (free ions)

Sources

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