Two different chemical elements, both alkali metals, both essential to the body and easily confused because they behave similarly. Sodium is element 11, symbol Na; potassium is element 19, symbol K. In the body they work as a pair across cell membranes, and most dietary advice concerns getting less sodium and more potassium.
The core difference
- sodium — symbol Na, atomic number 11
- potassium — symbol K, atomic number 19
Both are soft, highly reactive alkali metals that never occur free in nature — they are always found combined, most familiarly as salts.
Why the symbols look wrong
Neither symbol matches its English name, because both come from Latin: natrium for sodium and kalium for potassium. Those names survive in German and several other languages, and in words like natron and alkali. The English names are newer, coined when the elements were first isolated in 1807.
How they work together in the body
Cells maintain a difference in concentration across their membranes — sodium mostly outside, potassium mostly inside — and actively pump to keep it that way. That gradient is what makes nerve signalling and muscle contraction possible, including the heartbeat. This is why they are always discussed as a pair rather than separately.
In food
- Sodium reaches most people through salt, sodium chloride, and through processed food where it is used for preservation and flavour.
- Potassium is found in fruit, vegetables, pulses and dairy — bananas are the usual example, though beans and potatoes carry more.
Note that salt and sodium are not the same measure: table salt is about 40% sodium by weight, so a figure for salt is roughly two and a half times the figure for sodium.
Frequently asked questions
Why is potassium K and sodium Na?
The symbols come from their Latin names, kalium and natrium, which predate the English names coined when both were isolated in 1807.
Are sodium and salt the same thing?
No. Table salt is sodium chloride and is about 40% sodium by weight, so a salt figure is roughly 2.5 times the sodium figure.
Why are sodium and potassium always mentioned together?
Cells keep sodium mostly outside and potassium mostly inside, and that gradient drives nerve signalling and muscle contraction, including the heartbeat.