Potassium

Potassium is a <a href="/facts/Chemical_element/0jducgWD">chemical element</a>; it has <a href="/facts/Symbol_(chemistry)/2Fe1VAL0">symbol</a> K (from <a href="/facts/Neo-Latin/mbBrTVEd">Neo-Latin</a> kalium) and <a href="/facts/Atomic_number/bgAr581S">atomic number</a> 19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric <a href="/facts/Oxygen/acyn6o8r">oxygen</a> to form flaky white <a href="/facts/Potassium_peroxide/5AQySWhT">potassium peroxide</a> in only seconds of exposure. It was first isolated from <a href="/facts/Potash/4e2vBL9L">potash</a>, the ashes of plants, from which its name derives. In the <a href="/facts/Periodic_table/umdGIfUb">periodic table</a>, potassium is one of the <a href="/facts/Alkali_metal/IkWbCLk2">alkali metals</a>, all of which have a single <a href="/facts/Valence_electron/mXPA15VP">valence electron</a> in the outer electron shell, which is easily removed to create <a href="/facts/Cation/wrbwhF3z">an ion with a positive charge</a> (which combines with <a href="/facts/Anion/wrbwhF3z">anions</a> to form <a href="/facts/Salts/Fp0KhqyY">salts</a>). In nature, potassium occurs only in ionic salts. Elemental potassium reacts vigorously with water, generating sufficient heat to ignite <a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a> emitted in the reaction, and burning with a <a href="/facts/Lilac/7xgwB0l4">lilac</a>-<a href="/facts/Flame_color/EcpqRIt7">colored flame</a>. It is found dissolved in seawater (which is 0.04% potassium by weight), and occurs in many <a href="/facts/Mineral/LkUFbNmv">minerals</a> such as <a href="/facts/Orthoclase/xTjjm0gP">orthoclase</a>, a common constituent of <a href="/facts/Granite/G2evuVKo">granites</a> and other <a href="/facts/Igneous_rock/xeMJhUah">igneous rocks</a>.
Potassium is chemically very similar to <a href="/facts/Sodium/eYuSPu2V">sodium</a>, the previous element in <a href="/facts/Group_(periodic_table)/YGBcUabv">group</a> 1 of the periodic table. They have a similar first <a href="/facts/Ionization_energy/lezUajfA">ionization energy</a>, which allows for each atom to give up its sole outer electron. It was first suggested in 1702 that they were distinct elements that combine with the same anions to make similar salts, which was demonstrated in 1807 when elemental potassium was first isolated via <a href="/facts/Electrolysis/pU75nCDI">electrolysis</a>. Naturally occurring potassium is composed of three <a href="/facts/Isotope/KD9B1y6o">isotopes</a>, of which <a href="/facts/Potassium-40/RMnkrhvc">40K</a> is <a href="/facts/Radioactive/Ya6FVjt4">radioactive</a>. Traces of 40K are found in all potassium, and it is the most common <a href="/facts/Radioisotope/5WpCfbdq">radioisotope</a> in the human body.
Potassium ions are vital for the functioning of all living cells. The transfer of potassium ions across nerve cell membranes is necessary for normal nerve transmission; potassium deficiency and excess can each result in numerous signs and symptoms, including an abnormal heart rhythm and various <a href="/facts/Electrocardiographic/YpVswJ0W">electrocardiographic</a> abnormalities. Fresh fruits and vegetables are good dietary sources of potassium. The body responds to the influx of dietary potassium, which raises <a href="/facts/Serum_(blood)/a22tvug9">serum</a> potassium levels, by shifting potassium from outside to inside cells and increasing potassium excretion by the kidneys.
Most industrial applications of potassium exploit the high <a href="/facts/Solubility/kLE9h3Jb">solubility</a> of its compounds in water, such as <a href="/facts/Saltwater_soap/4ec77I67">saltwater soap</a>. Heavy crop production rapidly depletes the soil of potassium, and this can be remedied with agricultural fertilizers containing potassium, accounting for 95% of global potassium chemical production.

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Potassium