Potassium
. Potassium, symbol K (from Latin kalium, “alkali”), chemically reactive, extremely soft metallic element. In group 1 (or Ia) of the periodic table (see Periodic Law ), potassium is one of the alkali metals . The atomic number of potassium is 19. PROPERTIES AND OCCURRENCE Potassium was discovered and named in 1807 by the British chemist Sir Humphry Davy . The metal is silvery white and can be cut with a knife. It has a hardness of 0.5. Potassium exists in three natural isotopic forms, with mass numbers 39, 40, and 41. Potassium-40 is radioactive and has a half-life of 1.28 billion years. The most abundant isotope is potassium-39. Several radioactive isotopes have been artificially prepared. Potassium melts at about 63° C (about 145° F), boils at about 760° C (about 1400° F), and has a specific gravity of 0.86; the atomic weight of potassium is 39.098. Potassium metal is prepared by the electrolysis of fused potassium hydroxide or of a mixture of potassium chloride and potassium fluorid