Physical and Chemical Properties of Potassium

Potassium is an alkali metal and is a part of group 1. Its symbol is K taken from its Latin name Kalium. Its atomic number is 19 and atomic weight is 39.098u. It is white with a silvery shine or luster. It is soft at room temperature. It has a low melting point (63.28 °C or 145.90 °F). Its boiling point is (760 °C or 1,400 °F). Potassium is a fine conductor of electricity and heat. 

Its electronic configuration is 2, 8, 8, 1 or we can say 1s2 2s2 2p6 3s2 3p6 4s1.


Potassium was first isolated from caustic potash KOH (molten) by electrolysis in 1807. It was done by Sir Humphry Davy. Potassium collected at the cathode.


A notable point is that the very first metal to be isolated by electrolysis is Potassium. Until then, Potassium and Sodium could not be distinguished from each other. Before potassium was recognized as an element, it was used to make soap by mixing potassium carbonate with animal fat.


Potassium is the seventh most abundant element found on Earth’s crust. It constitutes 2.6 percent of Earth’s mass. The element whose atomic number is 19 and atomic weight 39.098u has a melting point of 63.28°C and a boiling point of 760°C. Its specific gravity is 0.862 at 20°C. Potassium has two oxidation states +1 and -1(rarely). 

There are three isotopes for potassium which are naturally present: potassium-39, potassium-41, radioactive potassium-40. Several artificial isotopes have also been prepared. 


Since potassium is mainly present in igneous rocks, shale, and sediment in minerals like muscovite and orthoclase feldspar, it is difficult to procure the element itself. The fact that these minerals are insoluble in water makes the job tougher. Therefore, soluble potassium compounds such as carnallite (KMgCl3.6H2O), sylvite (KCl), polyhalite (K2Ca2Mg [SO4]4.2H2O), and langbeinite (K2Mg2 [SO4]3) which are found in ancient lake beds and sea beds are electrolyzed to obtain commercial compounds of potassium.

Another way to produce potassium is to do sodium reduction of molten potassium chloride, KCl, at 870°C. This is done by feeding molten KCl into a packed distillation column. Sodium vapor is passed up through the column alongside. More volatile potassium will be condensed at the top of the distillation tower. 


The element whose atomic number is 19 has 0.82 marking for electronegativity (according to Pauling). It has a density of 0.86 g.cm-3 at 0°C. It's Van der Waals radius measures to 0.235 nm. It has an ionic radius of 0.133 nm. The energy of the first isolation is 418.6 kJ.mol-1.


  • Reaction with air:

  • Though potassium is shiny when it’s cut, the reaction with air and moisture present in it tarnishes it. When potassium is burned in air, potassium superoxide (KO2) is formed. It is orange in color.

    K(s) + O2(g) → KO2(s)

  • Reaction with water:

  •  Potassium reacts rapidly and vigorously with water to form potassium hydroxide and hydrogen gas in the form of a colorless solution. The product is basic in nature. The reaction is exothermic. 

    2K(s) + 2H2O → 2KOH (aq) + H2 (g)

    The reaction is fast, higher than the rate of sodium reacting with water but lower than rubidium.

  • Reaction with halogens:

  • Formation of potassium halides occurs when potassium reacts with halogens. The reaction is quite vigorous.

    2K(s) + F2 (g) → KF(s) potassium fluoride

    2K(s) + Cl2 (g) → KCl(s) potassium chloride

    2K(s) + Br2 (g) → KBr(s) potassium bromide

    2K(s) + I2 (g) → KI(s) potassium iodide

  • Reaction with acids:

  • Potassium dissolves readily in dilute sulphuric acid to form solutions containing the aquated K (I) ion together with hydrogen gas.

    2K(s) + H2SO4 (aq) → 2K+ (aq) + SO42-(aq) + H2 (g)

  • Potassium oxide is an ionic compound of potassium and oxygen. Since it is highly reactive, it turns into a mixture of potassium peroxide and potassium superoxide. Treatment of potassium peroxide yields potassium oxide.

  • K2O2 + 2 K → 2 K2O


    Since potassium forms a lot of compounds, it is a very useful element. Potassium chloride (KCl) can be called as the most common potassium compound. It is used in fertilizers and also as a salt substitute. It can be used to produce other chemicals as well. Potassium hydroxide (KOH) is used in the manufacture of soaps, detergents and drain cleaners. Potassium carbonate (KHCO3) is used to make certain types of glass and soaps. It is obtained as a byproduct of the commercial production of ammonia. KHCO3 is also known as pearl ash. Potassium nitrate (KNO3) is used in the production of fertilizers, match heads and also pyrotechnics.