Translations:Potassium/1/en

This page is about the chemical element. For the use of potassium as a medication, see Potassium chloride (medical use). For the use of potassium in biology, see Potassium in biology.

Potassium, ₁₉K

Potassium pearls (in paraffin oil, ~5 mm each)
Potassium
Appearance	silvery white, faint bluish-purple hue when exposed to air
Standard atomic weight Ar°(K)
	39.0983±0.0001  39.098±0.001 (abridged)
Potassium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson ↑ K ↓ ← potassium →
Atomic number (Z)	19
Electron configuration	[Ar] 4s1
Electrons per shell	2, 8, 8, 1
Physical properties
Phase at STP	solid
Melting point	336.7 K ​(63.5 °C, ​146.3 °F)
Boiling point	1030.793 K ​(757.643 °C, ​1395.757 °F)
Density (at 20° C)	0.8590 g/cm3
when liquid (at m.p.)	0.82948 g/cm3
Critical point	2223 K, 16 MPa
Heat of fusion	2.33 kJ/mol
Heat of vaporization	76.9 kJ/mol
Molar heat capacity	29.6 J/(mol·K)
Atomic properties
Oxidation states	−1, +1 (a strongly basic oxide)
Electronegativity	Pauling scale: 0.82
Ionization energies	1st: 418.8 kJ/mol 2nd: 3052 kJ/mol 3rd: 4420 kJ/mol (more)
Atomic radius	empirical: 227 pm
Covalent radius	203±12 pm
Van der Waals radius	275 pm
Color lines in a spectral range Spectral lines of potassium
Other properties
Natural occurrence	primordial
Crystal structure	​body-centered cubic (bcc) (cI2)
Lattice constant	a = 532.69 pm (at 20 °C)
Thermal expansion	77.37×10−6/K (at 20 °C)
Thermal conductivity	102.5 W/(m⋅K)
Electrical resistivity	72 nΩ⋅m (at 20 °C)
Magnetic ordering	paramagnetic
Molar magnetic susceptibility	+20.8×10−6 cm3/mol (298 K)
Young's modulus	3.53 GPa
Shear modulus	1.3 GPa
Bulk modulus	3.1 GPa
Speed of sound thin rod	2000 m/s (at 20 °C)
Mohs hardness	0.4
Brinell hardness	0.363 MPa
CAS Number	7440-09-7
History
Discovery and first isolation	Humphry Davy (1807)
Symbol	"K": from New Latin kalium
Isotopes of potassium
Main isotopes Decay abun­dance half-life (t1/2) mode pro­duct 39K stable 40K 1.248×109 y β− 40Ca ε 40Ar β+ 40Ar 41K stable