Overview

Potassium is a chemical element found among the alkali metals of the periodic table: see periodic table. Its chemical symbol is K, derived from the Latin name kalium, and its atomic number is 19. A neutral potassium atom contains 19 protons and 19 electrons. In nature potassium does not occur in the free metallic state because it reacts readily with air and water.

Physical and chemical properties

Potassium is a soft, silvery metal that can be cut with a knife and is less dense than water. It belongs to Group 1 and shares many traits with sodium and other alkali metals: it is electropositive, has a single valence electron, and ignites or reacts vigorously when exposed to moisture. The familiar lilac or violet color produced in a flame test is a diagnostic property used in qualitative analysis.

Occurrence, minerals and production

Potassium is abundant in the Earth's crust but is found combined in salts and minerals rather than as a pure element. Common potassium-bearing minerals include sylvite (potassium chloride) and various evaporite and igneous minerals. Commercial production of potassium compounds (often called potash) comes from mining these deposits and from processing brines; potassium metal itself is prepared by chemical reduction or electrochemical methods and must be handled under oil to prevent reactions with air or water.

Biological role and uses

Elemental potassium is not ingested, but dissolved potassium ions (K+) are essential to life. Potassium is the principal intracellular cation in animal cells and is central to nerve conduction, muscle contraction and maintaining cellular fluid balance. Plants require potassium as a macronutrient; this underlies the widespread use of potassium compounds in fertilizers such as potassium chloride and potassium sulfate. Industrially, potassium hydroxide and potassium carbonate are important chemicals in manufacturing, and potassium nitrate has historical use in gunpowder and modern use as an oxidizer.

Isotopes and geochronology

Natural potassium includes several isotopes. Two stable isotopes are recognized: 39K and 41K, which differ by the number of neutrons. A radioactive isotope, 40K, decays slowly and is present in small amounts; its decay to argon-40 provides a basis for potassium-argon dating used in geology and archaeology. The standard atomic mass for potassium is approximately 39.10 atomic mass units (u).

History, safety and notable facts

Potassium was first isolated by Sir Humphry Davy in 1807 by electrolysis of potash (potassium hydroxide), and its name reflects historical alkali sources. Metallic potassium must be stored and handled carefully because of its reactivity; contact with water produces potassium hydroxide and hydrogen gas, which can ignite. Many potassium salts are safe and nutritionally important, but excessive intake or impaired kidney function can create dangerous electrolyte imbalances. For further technical summaries and data, see entries in standard references: element tables, specialized isotope pages at atomic number resources, and chemical safety guides at elemental data and periodic resources.

  • Common compounds: KCl, K2SO4, KOH, KNO3.
  • Key uses: fertilizers, industrial chemicals, laboratory reagents, geochronology.
  • Notable property: characteristic lilac flame color used in analysis.

For more on potassium's role in biology, chemistry and industry, consult introductory chemistry texts and reputable online resources: see symbol reference, isotope summaries at isotope databases, and atomic mass tables at mass listings.