Potassium (K)

Isotopes of potassium available from ISOFLEX

Isotope Z(p) N(n) Atomic Mass Natural Abundance Enrichment Level Chemical Form
K-39 19 20 38.9637069 93.26% >99.90% Chloride
K-40 19 21 39.9639985 0.01% 5.00-16.95% Chloride
K-41 19 22 40.9618260 6.73% >95.00% Chloride

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Potassium was discovered in 1807 by Sir Humphry Davy. Its name originates with the English word potash (“pot ashes”) and the Arabic word qali (meaning “alkali”). The origin of the symbol K is the Latin word kalium (“alkali”). It is an essential element needed for plant growth. Potassium deficiency has also been associated with several common animal ailments. It is in extracellular fluid in animals, at lower concentrations than sodium.

A soft, silvery metal, potassium has a body-centered cubic structure that rapidly oxidizes in moist air and imparts a crimson-red color to flame. It is soluble in liquid ammonia, aniline, mercury and sodium. It reacts violently with water and acids, reacts with alcohol, and dissolves in liquid ammonia and mercury. It also reacts with oxygen or air, forming three oxides: potassium monoxide, potassium peroxide and potassium superoxide. Reactions with halogens, fluorine, chlorine and bromine occur with explosive violence. Violent reactions can occur with many metal halides as well.

Potassium products have applications in the bleaching of textiles and straw, in the tanning of leather, and in the food industry — potassium is the main ingredient in baking powder, it improves dough strength and rise height, and it is a preservative in wine- and beer-making. Potassium nitrate is used in gunpowder and fertilizer. Potassium cyanide is used in mining and in organic synthesis. Potassium carbonate is used in glass, soap, fluorescent lamps, textile dyes and pigments. Potassium chlorate is added to matches and explosives. Potassium bromide was formerly used as a sedative and in photography.

Properties of Potassium

Name Potassium
Symbol K
Atomic number 19
Atomic weight 39.098
Standard state Solid at 298 °K 
CAS Registry ID 7440-09-7 
Group in periodic table
Group name Alkali metal 
Period in periodic table
Block in periodic table s-block 
Color Silvery white 
Classification Metallic 
Melting point 63.25 °C
Boiling point 760 °C
Thermal conductivity 102.5 W/(m·K) at 298.2 °K
Electrical resistivity 6.1 µΩ·cm at 0 °C
Electronegativity 0.8 
Specific heat 0.75 kJ/kg K
Heat of vaporization 76.9 kJ·mol-1 at 760 °C
Heat of fusion 2.33 kJ·mol-1
Density of liquid 0.819 g/cm3 at 100 ºC and 0.771 g/cm3 at 300 ºC 
Density of solid 0.862 g/cm3 at 20 ºC
Electron configuration [Ar]4s
Atomic radius 2.35 Å 
Oxidation state +1 
Ionization potential  4.341 eV

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