Potassium

Source of the photo
http://periodictable.com/Elements/019/index.html
Author of the description
Gruiz Katalin

Atomic number

19

Atomic mass

39.0983 g.mol -1

Electronegativity

0.8

Density

0.86 g.cm -3 at 0 °C

Melting point

63.2 °C

Boiling point

760 °C

Vanderwaals radius

0.235 nm

Ionic radius

0.133 (+1)

Isotopes

5

Electronic shell

[ Ar ] 4s1

Energy of first ionisation

418.6 kJ.mol -1

Discovered by

Sir Davy in 1808

 


The name is derived from the english word potash. The chemical symbol K comes from kalium, the Mediaeval Latin for potash, which may have derived from the arabic word qali, meaning alkali.
Potassium is a soft, silvery-white metal, member of the alkali group of the periodic chart. Potassium is silvery when first cut but it oxidizes rapidly in air and tarnishes within minutes, so it is generally stored under oil or grease. It is light enough to float into water with which it reacts instantly to release hydrogen, which burns with a lilac flame.

The chemistry of potassium is almost etirely that of the potassium ion, K+.

Applications

Most potassium (95 %) goes into fertilizers and the rest goes mainly into making potassium hydroxide (KOH), by the electrolysis of potassium chloride solution, and then converting this to potassium carbonate (K2CO3). Potassium carbonate goes into glass manufacture, expecially the glass used to make televisions, while potassium hydroxide is used to make liquid soaps and detergents. A little potassium chloride goes into pharmaceuticals, medical drips and saline injections.
Other potassium salts are used in baking, photography and tanning leather, and to make iodize salts. In all cases it is the negative anion, not the potassium, which is the key to their use.