Potassium
alkali metalProperties
| Property | Value |
|---|---|
| Atomic Mass | 39.098 amu |
| Category | alkali metal |
| Group | 1 |
| Period | 4 |
| Electron Configuration | 1s2 2s2 2p6 3s2 3p6 4s1 |
| Electronegativity | 0.82 (Pauling) |
| Oxidation States | 1 |
| Melting Point | 336.7 K (63.6 °C) |
| Boiling Point | 1032 K (758.9 °C) |
| Density | 0.862 g/cm³ |
| Discovered By | Humphry Davy (1807) |
About Potassium
Potassium is the alkali metal that taught chemists what electrolysis could really do. Humphry Davy passed current through molten KOH in 1807 and watched the first beads of metal coalesce — the first metallic element ever isolated by an electric current. The symbol K survives from kalium, the Latinized form of the Arabic al-qalyah for plant ashes, the original source of potash before mining took over. Drop a chunk of the metal into water and the 4s¹ electron leaves so eagerly that the released hydrogen ignites with the characteristic lilac flame from the 766.5 nm and 769.9 nm K-D lines — the same emission lines that show up in flame photometry to quantify K⁺ in serum and soil samples. Biologically, the Na⁺/K⁺ ATPase pump moves three Na⁺ out and two K⁺ in per ATP hydrolyzed, maintaining the resting membrane potential that makes every nerve impulse and muscle contraction work. Industrially, almost all mined potash (K₂O equivalent, mostly as KCl from sylvite deposits in Saskatchewan and Belarus) goes straight to fertilizer for crops that can't access enough K from soil clays.
Fun Fact
Every banana is very slightly radioactive because it contains potassium, and about 0.012% of all potassium is the radioactive isotope K-40 — but you would need to eat roughly 10 million bananas at once to receive a lethal radiation dose.
Common Uses
- Potassium chloride (muriate of potash) as the dominant K source in NPK fertilizers
- KOH (caustic potash) for liquid soaps, biodiesel transesterification, and alkaline batteries
- Potassium nitrate (saltpeter) in black powder, fertilizer blends, and food curing
- K₂Cr₂O₇ and KMnO₄ as benchtop oxidizers in titrations and organic synthesis
- IV potassium chloride and oral KCl tablets to correct hypokalemia in clinical settings