Potassium
alkali metal · period 4 · group 1 (alkali metals (and hydrogen)) · s-block
Potassium is a chemical element with the symbol K (from Neo-Latin kalium) and atomic number 19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force.
What the numbers say
At standard temperature and pressure Potassium is a solid, sitting in period 4, group 1 of the s-block.
Its melting point of 337 K (64 °C) is the 91st highest of the 110 elements with a measured value — mid-range among the elements.
At 0.856 g/cm³ it is the 84th densest of 96 elements with a quoted density.
Pauling electronegativity is 0.82. Paired with oxygen (3.44) that is a difference of 2.62, which puts the bond predominantly ionic — expect a stable oxide ceramic.
In the solid state it takes a body-centered cubic structure — BCC packing is stronger but shows a ductile-to-brittle transition as temperature drops.
It is reported in 2 oxidation states (-1, 1), which sets how many distinct compounds and phases it can form.
First identified in 1807.
Crystal structure
Solid Potassium adopts a Body-centered Cubic arrangement, in the Cubic (isometric) system — axes a = b = c, angles α = β = γ = 90°. Symmetry controls the anisotropy of stiffness and thermal expansion, and the available slip systems set how far the metal deforms before it fractures.
Check it against computed structures
The structure search queries the Materials Project, OQMD and the Open Materials Database for computed crystal structures containing K — with DFT formation energy, hull stability and band gap where the provider publishes them.
K 2 · L 8 · M 8 · N 1
Properties
| Atomic number | 19 |
|---|---|
| Atomic mass | 39.09831 u |
| Series | alkali metal |
| Group | 1 |
| Period | 4 |
| Block | s-block |
| Phase at STP | Solid |
| Density | 0.856 g/cm³ |
| Melting point | 336.7 K (64 °C) |
| Boiling point | 1032 K (759 °C) |
| Electronegativity (Pauling) | 0.82 |
| Electron configuration | [Ar] 4s¹ |
| Crystal structure | Body-centered Cubic |
| Oxidation states | -1,1 |
| Discovered | 1807 |
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See K in context with all 118 elements.
Working with potassium in a real design?
Ask the materials chat how K behaves in your alloy system, what it does to weldability, and which grades to look at — with the source of every number named.