019Alkali metal · Group 1 · Period 4
Potassium
Potassium (K) is element 19, a alkali metal in the s-block — group 1, period 4. It is a solid at room temperature with 4 electron shells (2, 8, 8, 1) and an atomic mass of 39.09831 u.
- Atomic mass
- 39.10 u
- Phase · STP
- solid
- Melting
- 337 K · 64 °C
- Boiling
- 1032 K · 759 °C
- Electronegativity
- 0.82
- Density
- 0.862 g/cm³
Photograph — Dnn87, CC BY 3.0 <https://creativecommons.org/licenses/by/3.0>, via Wikimedia Commons
Emission spectrum
The visible light Potassium emits when energised — its unique spectral fingerprint.
Identity
- Atomic number
- 19
- Standard atomic weight
- 39.10 u
- Category
- Alkali metal
- Group
- 1 · Alkali metals
- Period
- 4
- Block
- s-block
- Oxidation states
- +1
Physical properties
- Melting point
- 337 K · 64 °C
- Boiling point
- 1032 K · 759 °C
- Density
- 0.862 g/cm³
- Molar heat capacity
- 29.6 J/(mol·K)
- Atomic radius
- 275 pm
- Electron affinity
- 48.383 kJ/mol
Atomic structure
19protons
20neutrons
19electrons
1valence e⁻
- Noble-gas notation
- [Ar] 4s1
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s1
- Electrons per shell
- 2, 8, 8, 1
Periodic trends
Where Potassium ranks across all 118 elements.
Ionization energies
Energy to remove each successive electron (kJ/mol).
418.81
3.1k2
4.4k3
5.9k4
8.0k5
9.6k6
11.3k7
14.9k8
17.0k9
48.6k10
Successive ionization energies (kJ/mol, log scale).
Discovery
- Discovered
- 1807
- Discovered by
- Humphry Davy
- Named by
- —
- Appearance
- silvery gray