Potassium
Symbol |
Name |
Atomic Number |
Atomic Weight |
Group Number |
K |
Potassium |
19 |
39.098 |
1 |
Standard Sate: solid at 298 K
Color: silvery white
The metal is the seventh most abundant and makes up about 1.5 % by weight of the earth's crust. Potassium is an essential constituent for plant growth and it is found in most soils. It is also a vital element in the human diet.
(K), chemical element of Group Ia of the periodic table, the alkali
metal group, indispensable for life. Potassium was the first metal to
be isolated by electrolysis, by the English chemist Sir Humphry Davy,
when he obtained the element (1807) by decomposing molten
potassium hydroxide (KOH) with a voltaic battery.
Properties, occurrence, and uses.
Potassium metal is soft and white with a silvery lustre, has a low
melting point, and is a good conductor of heat and electricity.
Potassium imparts a lavender colour to a flame, and its vapour is
green. It is the seventh most abundant element in the Earth's crust,
constituting 2.6 percent of its material. Most potassium is present in
minerals such as muscovite and orthoclase feldspar that are insoluble
in water, making potassium difficult to obtain, but it can be prepared
commercially by electrolysis from some refinable minerals, such as
carnallite and polyhalite.
There is little commercial demand for potassium metal itself, though
it is used for preparing potassium superoxide, KO2, which
refreshens exhaled air by liberating oxygen and removing carbon
dioxide and water vapour, and for alloying with sodium as a liquid
metallic heat-transfer medium. Potassium reacts vigorously with
water, liberating hydrogen (which ignites) and forming a solution of
potassium hydroxide, KOH. In plant metabolism, potassium
compounds are absorbed from soil in the form of tartrates and
oxalates, which may be converted to potassium carbonate (potash)
when the plants are burned. In higher animals potassium ions (K+)
together with sodium ions act at cell membranes in transmitting
electrochemical impulses in nerve and muscle fibres and in balancing
the activity of food intake and waste removal from cells. Too little or
too much potassium in the body is fatal, but potassium in the soil
ensures the presence of this indispensable element in food.
Natural potassium consists of three isotopes: potassium-39 (93.26
percent), potassium-41 (6.73 percent), and radioactive
potassium-40 (about 0.01 percent); several artificial isotopes have
also been prepared. Potassium easily loses the single 4s electron, so
it has a valence of one in all its compounds.
Principal compounds.
Potassium compounds are very important in agriculture and to lesser
extent in the manufacture of explosives. Potassium chloride, KCl, is
a naturally occurring potassium salt that is used as fertilizer and as a
raw material for the production of other important potassium
compounds. Electrolysis of potassium chloride yields potassium
hydroxide (also called caustic potash), which readily absorbs moisture
and is employed in making liquid soaps and detergents and in
preparing many potassium salts. Reaction of iodine and potassium
hydroxide produces potassium iodide, KI, which is added to table salt
and animal feed to protect against iodine deficiency.
Other potassium compounds of economic value include potassium
nitrate, also known as saltpetre, or nitre, KNO3, which has wide use
as a fertilizer and in fireworks and explosives and serves as a food
preservative; potassium chromate, K2CrO4, which is employed in
tanning leather and dyeing textiles; and potassium sulfate, K2SO4,
which is used in the production of fertilizers and potassium alums.
atomic number 19 atomic weight 39.098 melting point 63.28 C
(145.90 F) boiling point 760 C (1400 F) specific gravity 0.862 (20
C) valence 1 electronic config. 2-8-8-1 or 1s22s22p63s23p64s1
"potassium" Encyclop�dia Britannica Online.
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