Potassium information

Potassium, ₁₉K
	Potassium pearls (in paraffin oil, ~5 mm each)
Potassium
Appearance	silvery white, faint bluish-purple hue when exposed to air
Standard atomic weight Ar°(K)
	39.0983±0.0001; 39.098±0.001 (abridged);
Potassium in the periodic table
	argon ← potassium → calcium
Atomic number (Z)	19
Group	group 1: hydrogen and alkali metals
Period	period 4
Block	s-block
Electron configuration	[Ar] 4s1
Electrons per shell	2, 8, 8, 1
Physical properties
Phase at STP	solid
Melting point	336.7 K (63.5 °C, 146.3 °F)
Boiling point	1030.793 K (757.643 °C, 1395.757 °F)
Density (at 20° C)	0.8590 g/cm3
when liquid (at m.p.)	0.82948 g/cm3
Critical point	2223 K, 16 MPa
Heat of fusion	2.33 kJ/mol
Heat of vaporization	76.9 kJ/mol
Molar heat capacity	29.6 J/(mol·K)
Atomic properties
Oxidation states	−1, +1 (a strongly basic oxide)
Electronegativity	Pauling scale: 0.82
Ionization energies	1st: 418.8 kJ/mol ; 2nd: 3052 kJ/mol ; 3rd: 4420 kJ/mol ; (more) ;
Atomic radius	empirical: 227 pm
Covalent radius	203±12 pm
Van der Waals radius	275 pm
	Spectral lines of potassium
Other properties
Natural occurrence	primordial
Crystal structure	body-centered cubic (bcc) (cI2)
Lattice constant	a = 532.69 pm (at 20 °C)
Thermal expansion	77.37×10−6/K (at 20 °C)
Thermal conductivity	102.5 W/(m⋅K)
Electrical resistivity	72 nΩ⋅m (at 20 °C)
Magnetic ordering	paramagnetic
Molar magnetic susceptibility	+20.8×10−6 cm3/mol (298 K)
Young's modulus	3.53 GPa
Shear modulus	1.3 GPa
Bulk modulus	3.1 GPa
Speed of sound thin rod	2000 m/s (at 20 °C)
Mohs hardness	0.4
Brinell hardness	0.363 MPa
CAS Number	7440-09-7
History
Discovery and first isolation	Humphry Davy (1807)
Symbol	"K": from New Latin kalium
Isotopes of potassium v; e;
ε	40Ar
β+	40Ar
	Category: Potassium; view; talk; edit; \| references

Potassium is a chemical element; it has symbol K (from Neo-Latin kalium) and atomic number 19. It is a silvery white metal that is soft enough to easily cut with a knife.^[8] Potassium metal reacts rapidly with atmospheric oxygen to form flaky white potassium peroxide in only seconds of exposure. It was first isolated from potash, the ashes of plants, from which its name derives. In the periodic table, potassium is one of the alkali metals, all of which have a single valence electron in the outer electron shell, which is easily removed to create an ion with a positive charge (which combines with anions to form salts). In nature, potassium occurs only in ionic salts. Elemental potassium reacts vigorously with water, generating sufficient heat to ignite hydrogen emitted in the reaction, and burning with a lilac-colored flame. It is found dissolved in seawater (which is 0.04% potassium by weight),^[9]^[10] and occurs in many minerals such as orthoclase, a common constituent of granites and other igneous rocks.^[11]

Potassium is chemically very similar to sodium, the previous element in group 1 of the periodic table. They have a similar first ionization energy, 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,^[12] which was demonstrated in 1807 when elemental potassium was first isolated via electrolysis. Naturally occurring potassium is composed of three isotopes, of which ⁴⁰
K is radioactive. Traces of ⁴⁰
K are found in all potassium, and it is the most common radioisotope 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 electrocardiographic abnormalities. Fresh fruits and vegetables are good dietary sources of potassium. The body responds to the influx of dietary potassium, which raises serum 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 solubility of its compounds in water, such as saltwater soap. 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.^[13]

^ "Standard Atomic Weights: Potassium". CIAAW. 1979.
^ Prohaska T, Irrgeher J, Benefield J, Böhlke JK, Chesson LA, Coplen TB, Ding T, Dunn PJ, Gröning M, Holden NE, Meijer HA (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.
^ ^a ^b Aitken F, Volino F (January 2022). "New equations of state describing both the dynamic viscosity and self-diffusion coefficient for potassium and thallium in their fluid phases". Physics of Fluids. 34 (1): 017112. doi:10.1063/5.0079944.
^ ^a ^b ^c Arblaster JW (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.
^ Haynes WM, ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 4.122. ISBN 1-4398-5511-0.
^ Magnetic susceptibility of the elements and inorganic compounds, in Lide DR, ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.
^ Weast R (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.
^ Augustyn A. "Potassium/ Chemical element". Encyclopedia Britannica. Archived from the original on 2019-07-09. Retrieved 2019-04-17. Potassium Physical properties
^ Webb DA (April 1939). "The Sodium and Potassium Content of Sea Water" (PDF). The Journal of Experimental Biology (2): 183. Archived (PDF) from the original on 2019-09-24. Retrieved 2017-07-23.
^ Anthoni J (2006). "Detailed composition of seawater at 3.5% salinity". seafriends.org.nz. Archived from the original on 2019-01-18. Retrieved 2011-09-23.
^ Halperin ML, Kamel KS (1998-07-11). "Potassium". The Lancet. 352 (9122): 135–140. doi:10.1016/S0140-6736(98)85044-7. ISSN 0140-6736. PMID 9672294. S2CID 208790031. Archived from the original on 2021-06-07. Retrieved 2021-06-07.
^ Cite error: The named reference 1702Suspect was invoked but never defined (see the help page).
^ Greenwood, p. 73

[1] "Standard Atomic Weights: Potassium". CIAAW. 1979.

[CIAAW2021-2] Prohaska T, Irrgeher J, Benefield J, Böhlke JK, Chesson LA, Coplen TB, Ding T, Dunn PJ, Gröning M, Holden NE, Meijer HA (2022-05-04). "Standard atomic weights of the elements 2021 (IUPAC Technical Report)". Pure and Applied Chemistry. doi:10.1515/pac-2019-0603. ISSN 1365-3075.

[aitK-3] Aitken F, Volino F (January 2022). "New equations of state describing both the dynamic viscosity and self-diffusion coefficient for potassium and thallium in their fluid phases". Physics of Fluids. 34 (1): 017112. doi:10.1063/5.0079944.

[Arblaster_2018-4] Arblaster JW (2018). Selected Values of the Crystallographic Properties of Elements. Materials Park, Ohio: ASM International. ISBN 978-1-62708-155-9.

[5] Haynes WM, ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 4.122. ISBN 1-4398-5511-0.

[6] Magnetic susceptibility of the elements and inorganic compounds, in Lide DR, ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.

[7] Weast R (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. ISBN 0-8493-0464-4.

[8] Augustyn A. "Potassium/ Chemical element". Encyclopedia Britannica. Archived from the original on 2019-07-09. Retrieved 2019-04-17. Potassium Physical properties

[seawaterconcentration-9] Webb DA (April 1939). "The Sodium and Potassium Content of Sea Water" (PDF). The Journal of Experimental Biology (2): 183. Archived (PDF) from the original on 2019-09-24. Retrieved 2017-07-23.

[10] Anthoni J (2006). "Detailed composition of seawater at 3.5% salinity". seafriends.org.nz. Archived from the original on 2019-01-18. Retrieved 2011-09-23.

[11] Halperin ML, Kamel KS (1998-07-11). "Potassium". The Lancet. 352 (9122): 135–140. doi:10.1016/S0140-6736(98)85044-7. ISSN 0140-6736. PMID 9672294. S2CID 208790031. Archived from the original on 2021-06-07. Retrieved 2021-06-07.

[1702Suspect-12] Cite error: The named reference 1702Suspect was invoked but never defined (see the help page).

[g73-13] Greenwood, p. 73

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