HISTORICAL INFORMATION Discovered by: Sir Humphrey Davy Discovered at: England Discovered when: 1807 Origin of name: From the English word "potash" (pot ashes) and the Arabic word "qali" meaning alkali (the origin of the symbol K comes from the Latin word "kalium")

POTASSIUM Symbol : K Atomic number : 19 Atomic weight : 39,0983 Group number : 1 Group name : alkali metal Period number : 4 Block : s-block Standard state : solid at 298 K Colour : silvery white Classification : Metallic 293 K : g/cm3 Melting point : K (63.38°C) Boiling point : 1032 K (759°C)

Electronegativity: 0.82 Energy ionization : - 1st ionization energy : kJ/mole - 2nd ionization energy : kJ/mole - 3rd ionization energy : kJ/mole Electron affinity: kJ/mole Isotope: 39 K, 40 K, 41 K Electron configuration : [Ar] 4s1 Structure : body-centered cubic

Isolation Potassium is not made by the same method as sodium as might have been expected. This is because the potassium metal, once formed by electrolysis of liquid potassium chloride (KCl), is too soluble in the molten salt. cathode: K + (l) + e -  K (l) anode: Cl - (l)  1/2Cl 2 (g) + e - Instead, it is made by the reaction of sodium vapor with molten potassium chloride. Na + KCl K + NaCl This is an equilibrium reaction and under these conditions the potassium is highly volatile and removed from the system in a form relatively free from sodium impurities, allowing the reaction to proceed.

Chemical reactions of the elements Reaction of potassium with air If potassium is burned in air, the result is mainly formation of orange potassium superoxide, KO 2. K(s) + O 2 (g)  KO 2 (s) Reaction of potassium with water Potassium metal reacts very rapidly with water to form a colourless solution of potassium hydroxide (KOH) and hydrogen gas (H2). The resulting solution is basic because of the dissolved hydroxide. The reaction is exothermic. 2K(s) + 2H 2 O  2KOH(aq) + H 2 (g) Reaction of potassium with acids Potassium metal dissolves readily in dilute sulphuric acid to form solutions containing the aquated K(I) ion together with hydrogen gas, H 2. 2K(s) + H 2 SO 4 (aq)  2K + (aq) + SO 4 2- (aq) + H 2 (g)

Reaction of potassium with the halogens Potassium metal reacts vigorously with all the halogens to form potassium halides. 2K(s) + F 2 (g)  KF(s) 2K(s) + Cl 2 (g)  KCl(s) 2K(s) + Br 2 (g)  KBr(s) 2K(s) + I 2 (g)  KI(s) Reaction of potassium with bases Potassium metal reacts very rapidly with water to form a colourless basic solution of potassium hydroxide (KOH) and hydrogen gas (H 2 ). The reaction is exothermic. 2K(s) + 2H 2 O  2KOH(aq) + H 2 (g) The picture shows the reaction between potassium metal and water.

Uses - The superoxide KO 2 is used in breathing apparatus where moisture in the breath and carbon dioxide reacts with it to release oxygen 2KO 2 + H 2 O + 2CO 2  2KHCO 3 + O 2 - the alloy of potassium with sodium (NaK) is used as a heat-transfer medium in nuclear reactors. - Fertilizers usually as the chloride, sulphate, nitrate, or carbonate possium nitrate, KNO3, and potassium chlorate, KClO 3, are used in fireworks - Potassium permanganate, KMnO4, is an important oxidizing agent low-sodium salt - Potassium hydroxide is used in the preparation of potassium phosphates for liquid detergents