Potassium (K)
Element 19 · Alkali metal · Solid at 25 °C · Group 1, Period 4
Potassium is an essential nutrient your nerves and muscles cannot work without — bananas are famous for it — and potassium compounds are a mainstay of fertilizer.
On the periodic table, potassium sits in group 1 — the alkali metal group — in period 4. It is one of 6 elements classified as an alkali metal, and at room temperature (25 °C) it is a solid.
The alkali metals are soft, silvery metals with a single electron in their outer shell — which they give up so easily that they are among the most reactive metals known. They react vigorously (sometimes violently) with water, tarnish in air within minutes, and are never found as free metals in nature. In the lab they are stored under oil to keep air and moisture away. Reactivity increases as you move down the group.
Properties of potassium
| Atomic number (Z) | 19 |
|---|---|
| Symbol | K |
| Atomic mass | 39.098 |
| Category | Alkali metal |
| Group | 1 |
| Period | 4 |
| Block | s-block |
| Metal / nonmetal | Metal |
| State at 25 °C | Solid |
| Electron configuration | [Ar] 4s1 |
| Electronegativity (Pauling) | 0.82 |
| Melting point | 63.5 °C (336.65 K / 146.3 °F) |
| Boiling point | 759 °C (1,032.15 K / 1,398.2 °F) |
| Density | 0.862 g/cm³ |
Position in the periodic table
Potassium shares group 1 — the alkali metal group with Hydrogen (H), Lithium (Li), Sodium (Na), Rubidium (Rb), Caesium (Cs), Francium (Fr). Elements in the same group have the same number of outer electrons, so they tend to behave alike chemically — comparing them is one of the fastest ways to see periodic trends in action.
Physical properties
Potassium melts at 63.5 °C (336.65 K / 146.3 °F) and boils at 759 °C (1,032.15 K / 1,398.2 °F), giving it a liquid range of about 695.5 °C at standard pressure.
Its density is 0.862 g/cm³.
See also: the interactive periodic table, how to read the periodic table, the element families tour.