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K

Potassium
19K
Na ? K ? Rb Periodic table argon ? potassium ? calcium
Appearance
silvery gray Potassium pearls under paraffin oil. The large pearl measures 0.5 cm. Below: spectral lines of potassium
General properties
Name, symbol, number	potassium, K, 19
Pronunciation	/p??tæsi?m/ po-TAS-ee-?m
Metallic category	alkali metal
Group, period, block	1, 4, s
Standard atomic weight	39.0983(1)
Electron configuration	[Ar] 4s1 2, 8, 8, 1
History
Discovery	Humphry Davy (1807)
First isolation	Humphry Davy (1807)
Physical properties
Phase	solid
Density (near r.t.)	0.862 g·cm?3
Liquid density at m.p.	0.828 g·cm?3
Melting point	336.53 K,?63.38 °C,?146.08 °F
Boiling point	1032 K,?759 °C,?1398 °F
Triple point	336.35 K (63°C),  kPa
Heat of fusion	2.33 kJ·mol?1
Heat of vaporization	76.9 kJ·mol?1
Molar heat capacity	29.6 J·mol?1·K?1
Atomic properties
Oxidation states	1 (strongly basic oxide)
Electronegativity	0.82 (Pauling scale)
Ionization energies (more)	1st: 418.8 kJ·mol?1
	2nd: 3052 kJ·mol?1
	3rd: 4420 kJ·mol?1
Atomic radius	227 pm
Covalent radius	203±12 pm
Van der Waals radius	275 pm
Miscellanea
Crystal structure	body-centered cubic
Magnetic ordering	paramagnetic
Electrical resistivity	(20 °C) 72 n?·m
Thermal conductivity	102.5 W·m?1·K?1
Thermal expansion	(25 °C) 83.3 µm·m?1·K?1
Speed of sound (thin rod)	(20 °C) 2000 m·s?1
Young's modulus	3.53 GPa
Shear modulus	1.3 GPa
Bulk modulus	3.1 GPa
Mohs hardness	0.4
Brinell hardness	0.363 MPa
CAS registry number	7440-09-7
Most stable isotopes
Main article: Isotopes of potassium
iso NA half-life DM DE (MeV) DP 39K 93.26% 39K is stable with 20 neutrons 40K 0.012% 1.248(3)×109 y ?? 1.311 40Ca ? 1.505 40Ar ?+ 1.505 40Ar 41K 6.73% 41K is stable with 22 neutrons
v t e · r

Potassium is a chemical element with symbol K (from Neo-Latin kalium) and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction and burning with a lilac flame.

Because potassium and sodium are chemically very similar, their salts were not at first differentiated. The existence of multiple elements in their salts was suspected from 1702,^[1] and this was proven in 1807 when potassium and sodium were individually isolated from different salts by electrolysis. Potassium in nature occurs only in ionic salts. As such, it is found dissolved in seawater (which is 0.04% potassium by weight^[2][3]), and is part of many minerals.

Most industrial chemical applications of potassium employ the relatively high solubility in water of potassium compounds, such as potassium soaps. Potassium metal has only a few special applications, being replaced in most chemical reactions with sodium metal.

Potassium ions are necessary for the function of all living cells. Potassium ion diffusion is a key mechanism in nerve transmission, and potassium depletion in animals, including humans, results in various cardiac dysfunctions. Potassium accumulates in plant cells, and thus fresh fruits and vegetables are a good dietary source of it. Conversely, most plants except specialist halophytes are intolerant of salt, and sodium is present in them only in low concentration. This resulted in potassium first being isolated from potash, the ashes of plants, giving the element its name. For the same reason, heavy crop production rapidly depletes soils of potassium, and agricultural fertilizers consume 95% of global potassium chemical production.^[4]