Sodium vs Potassium: Group 1 Neighbours in the 3D Periodic Table
Sodium and potassium sit one above the other in group 1, the alkali metals. Both are soft enough to cut with a knife and both react with water. Potassium, lower down the group, is bigger and reacts more violently. In your body, they work as a pair to carry nerve signals.
Sodium vs potassium at a glance
| Sodium | Potassium | |
|---|---|---|
| Symbol | Na, from the Latin natrium | K, from the Latin kalium |
| Atomic number | 11 | 19 |
| Atomic mass | 22.99 | 39.10 |
| Electron shells | 2, 8, 1 | 2, 8, 8, 1 |
| In water | Fizzes and whizzes around, may catch fire | Bursts into lilac flame straight away |
| Flame colour | Bright yellow-orange | Lilac |
| Melting point | About 98 °C | About 63 °C |
| In the body | Mostly outside cells | Mostly inside cells |
| Discovered | 1807, by Humphry Davy | 1807, by Humphry Davy, a few days earlier |
Why potassium is more reactive
Both have one electron in their outer shell, which they give away easily. Potassium has an extra shell, so its outer electron is further from the nucleus and more shielded by the electrons in between. It is held less tightly, so potassium loses it more easily and reacts faster.
A team in your body
Your cells pump sodium out and potassium in, using a protein called the sodium-potassium pump. This sets up a tiny electrical difference across every cell. When a nerve fires, sodium rushes in and potassium flows out, carrying the signal along. Salt gives us sodium; bananas, potatoes and beans are good sources of potassium.
Quick facts
- Both are stored under oil to stop them reacting with air and water.
- Both are less dense than water, so they float as they react.
- Humphry Davy discovered both by passing electricity through their melted compounds.
- Street lights once glowed orange from sodium vapour lamps.
- Table salt is sodium chloride; some low-salt products use potassium chloride instead.
Sodium vs potassium questions
Which is more reactive, sodium or potassium?
Potassium. Its outer electron is further from the nucleus, so it is lost more easily.
What group are sodium and potassium in?
Group 1, the alkali metals.
What colour flame do sodium and potassium give?
Sodium gives a bright yellow-orange flame; potassium gives a lilac flame.
Why is potassium’s symbol K?
It comes from its Latin name, kalium. Sodium’s symbol Na comes from natrium.
What do sodium and potassium do in the body?
They work together to keep the right balance of water and to carry nerve and muscle signals.
More face-offs: see all 3D comparisons.
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