Potassium
Soft silvery metallic element belonging to group 1 of the periodic table (alkali metals). Occurs naturally in seawater and a many minerals. Highly reactive, chemically, it resembles sodium in its behavior and compounds. Discovered by Sir Humphry Davy in 1807.
Gallery
Dnn87, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
Emission spectrum
Physical Propertiesmass · density · phase · crystal
Atomic Mass
39.0983Da
Density
0.8900g/cm³
Phase (STP)
Solid
Melting Point
336.6K
Boiling Point
1032.2K
Molar Heat
0.7570J/(mol·K)
Crystal Structure
BCC
Lattice Constant
5.230Å
Atomic Radiiatomic · covalent · van der Waals
Atomic (Empirical)
220.00pm
Covalent
196.00pm
Van der Waals
275.00pm
Electronic Propertieselectronegativity · ionization · affinity
Electron Configuration
[Ar] 4s
Electron Shells
2, 8, 8, 1
Electronegativity
0.82Pauling
Electron Affinity
0.5kJ/mol
1st Ionization Energy
4.3kJ/mol
Oxidation States
+1
Orbital DiagramAufbau · Hund's rule · Pauli exclusion
Full: 1s2 2s2 2p6 3s2 3p6 4s1Short: [Ar] 4s
Ionization Energies (19 known)
Emission Spectrumvisible range · characteristic spectral lines
Abundanceby mass
Log scale · ppm = parts per million by mass
Biological Role
Major intracellular cation. Essential for nerve function, muscle contraction, and heart rhythm.
Discovery
Discovered By
Sir Humphrey Davy
Named By
—
Year
1807
Nuclear Data
Known Isotopes
29
Stable Isotopes
5
Stable Mass Numbers
32, 33, 34, 39, 41
Natural isotopic abundance (IUPAC recommended values)
Isotopes of K29 known
| Nuclide | Z | N | Mass (AMU) | Half-life | Decay | Jπ | Abundance |
|---|---|---|---|---|---|---|---|
| 31K | 19 | 12 | 31.036780 | Unknown | 3p (1%) | 3/2+ | — |
| 32Kstable | 19 | 13 | 32.023607 | Stable | p | 1+ | — |
| 33Kstable | 19 | 14 | 33.008095 | Stable | p | 3/2+ | — |
| 34Kstable | 19 | 15 | 33.998690 | Stable | p | 1+ | — |
| 39Kstable | 19 | 20 | 38.963706 | Stable | stable (1%) | 3/2+ | 9325.8100% |
| 40K | 19 | 21 | 39.963998 | 1.25 Gy | β⁻ (0.8928%), β⁺ (0.1072%) | 4- | 1.1700% |
| 41Kstable | 19 | 22 | 40.961825 | Stable | stable (1%) | 3/2+ | 673.0200% |
| 57K | 19 | 38 | 57.015169 | Unknown | β⁻, β⁻n, 2n | 3/2+ | — |
| 58K | 19 | 39 | 58.023543 | Unknown | β⁻, β⁻n, 2n | 2- | — |
| 59K | 19 | 40 | 59.030864 | Unknown | β⁻, β⁻n, 2n | 3/2+ | — |