Sodium (Na)

Sodium melts at 98 °C, so a lump of it turns liquid in hot water before it has finished reacting, which is exactly why the demonstration is so lively. Every nerve impulse in your body is a wave of sodium ions crossing a cell membrane, and the pump that moves them back out uses a substantial fraction of your resting energy budget. The metal was named by Davy from "soda", but its symbol comes from the Latin natrium, which is why sodium-potassium is written Na-K.

Properties

Atomic number

11

Symbol

Na

Standard atomic weight

22.99 u

Category

Alkali metal

Group

1

Period

3

Block

s-block

Electron configuration

[Ne] 3s¹

Electrons per shell

2, 8, 1

Melting point

370.95 K — 97.8 °C — 208.0 °F

Boiling point

1,156 K — 882.9 °C — 1621.1 °F

Density

0.97 g/cm³

Electronegativity

0.93 (Pauling)

Oxidation states

+1

Discovered

1807 by Humphry Davy

Electron configuration

Full

1s² 2s² 2p⁶ 3s¹

Noble gas shorthand

[Ne] 3s¹

Shells

K: 2 · L: 8 · M: 1

What it is used for

• Table salt and food preservation, as sodium chloride
• Sodium hydroxide for soap, paper and drain cleaner
• Sodium vapour street lamps, the orange ones
• Liquid-sodium coolant in fast breeder reactors
• Sodium bicarbonate in baking and in fire extinguishers

Hazards

• Reacts vigorously with water, releasing hydrogen that often ignites
• Must be stored under oil or in an inert atmosphere
• Sodium hydroxide is severely caustic to skin and eyes

Neighbours in the table

Group 1

Elements in the same group share their outer electron count, which is why they behave similarly in reactions. Sodium sits in group 1 with hydrogen, lithium, potassium, rubidium, cesium, francium.