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.[5] Potassium metal reacts rapidly with atmospheric oxygen to form flaky white potassium peroxide in only seconds of exposure. It was first isolated from potash, the ashes of plants, from which its name derives. In the periodic table, potassium is one of the alkali metals, all of which have a single valence electron in the outer electron shell, that is easily removed to create an ion with a positive charge – a cation, that combines with anions to form salts. Potassium in nature occurs only in ionic salts. Elemental potassium reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction, and burning with a lilac-colored flame. It is found dissolved in sea water (which is 0.04% potassium by weight[6][7]), and occurs in many minerals such as orthoclase, a common constituent of granites and other igneous rocks.[8]

Potassium, 19K
Potassium pearls (in paraffin oil, ~5 mm each)
Pronunciation/pəˈtæsiəm/ (pə-TASS-ee-əm)
Appearancesilvery gray
Standard atomic weight Ar, std(K)39.0983(1)[1]
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


Atomic number (Z)19
Groupgroup 1: hydrogen and alkali metals
Periodperiod 4
Block  s-block
Electron configuration[Ar] 4s1
Electrons per shell2, 8, 8, 1
Physical properties
Phase at STPsolid
Melting point336.7 K (63.5 °C, 146.3 °F)
Boiling point1032 K (759 °C, 1398 °F)
Density (near r.t.)0.89 g/cm3
when liquid (at m.p.)0.828 g/cm3
Critical point2223 K, 16 MPa[2]
Heat of fusion2.33 kJ/mol
Heat of vaporization76.9 kJ/mol
Molar heat capacity29.6 J/(mol·K)
Atomic properties
Oxidation states−1, +1 (a strongly basic oxide)
ElectronegativityPauling scale: 0.82
Ionization energies
  • 1st: 418.8 kJ/mol
  • 2nd: 3052 kJ/mol
  • 3rd: 4420 kJ/mol
  • (more)
Atomic radiusempirical: 227 pm
Covalent radius203±12 pm
Van der Waals radius275 pm
Color lines in a spectral range
Spectral lines of potassium
Other properties
Natural occurrenceprimordial
Crystal structure body-centered cubic (bcc)
Speed of sound thin rod2000 m/s (at 20 °C)
Thermal expansion83.3 µm/(m⋅K) (at 25 °C)
Thermal conductivity102.5 W/(m⋅K)
Electrical resistivity72 nΩ⋅m (at 20 °C)
Magnetic orderingparamagnetic[3]
Molar magnetic susceptibility+20.8×10−6 cm3/mol (298 K)[4]
Young's modulus3.53 GPa
Shear modulus1.3 GPa
Bulk modulus3.1 GPa
Mohs hardness0.4
Brinell hardness0.363 MPa
CAS Number7440-09-7
Discovery and first isolationHumphry Davy (1807)
Symbol"K": from New Latin kalium
Main isotopes of potassium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
39K 93.258% stable
40K 0.012% 1.248×109 y β 40Ca
ε 40Ar
β+ 40Ar
41K 6.730% stable
 Category: Potassium
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Potassium is chemically very similar to sodium, the previous element in group 1 of the periodic table. They have a similar first ionization energy, which allows for each atom to give up its sole outer electron. It was suspected in 1702 that they were distinct elements that combine with the same anions to make similar salts,[9] and was proven in 1807 using electrolysis. Naturally occurring potassium is composed of three isotopes, of which 40
is radioactive. Traces of 40
are found in all potassium, and it is the most common radioisotope in the human body.

Potassium ions are vital for the functioning of all living cells. The transfer of potassium ions across nerve cell membranes is necessary for normal nerve transmission; potassium deficiency and excess can each result in numerous signs and symptoms, including an abnormal heart rhythm and various electrocardiographic abnormalities. Fresh fruits and vegetables are good dietary sources of potassium. The body responds to the influx of dietary potassium, which raises serum potassium levels, with a shift of potassium from outside to inside cells and an increase in potassium excretion by the kidneys.

Most industrial applications of potassium exploit the high solubility in water of potassium compounds, such as potassium soaps. Heavy crop production rapidly depletes the soil of potassium, and this can be remedied with agricultural fertilizers containing potassium, accounting for 95% of global potassium chemical production.[10]