Potassium (K)

Science / Periodic Table of Elements / Potassium (K): 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. Potassium in the environment: Most potassium occurs in the Earth's crust as minerals, such as feldspars and clays. Potassium is leached from these by weathering, which explains why there is quite a lot of this element in the sea (0.75 g/liter). Minerals mined for their potassium are pinkish and sylvite, carnallite and alunite. The main mining area used to be Germany, which had a monopoly of potassium before the first World War. Today most potassium minerals come from Canada, USA and Chile. The world production of potassim ores is about 50 million tonnes, and reserves are vast (more than 10 billion tonnes). Potassium is a key plant element. Although it is soluble in water, little is lost from undisturbed soils because as it is released from dead plants and animal excrements, it quickly become strongly bound to clay particles, and it is retained ready to be readsorbed by the roots of other plants. Read more: http://www.lenntech.com/periodic/elements/k.htm#ixzz0eb4AA5WT

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