Potassium

Potassium, 19K
Potassium pearls (in paraffin oil, ~5 mm each)
Potassium
Appearancesilvery white, faint bluish-purple hue when exposed to air
Standard atomic weight Ar°(K)
Potassium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Na

K

Rb
argonpotassiumcalcium
Atomic number (Z)19
Groupgroup 1: hydrogen and alkali metals
Periodperiod 4
Block  s-block
Electron configuration[Ar] 4s1
Electrons per shell2, 8, 8, 1
Physical properties
Phase at STPsolid
Melting point336.7 K ​(63.5 °C, ​146.3 °F)
Boiling point1030.793 K ​(757.643 °C, ​1395.757 °F)[3]
Density (at 20° C)0.8590 g/cm3[4]
when liquid (at m.p.)0.82948 g/cm3[3]
Critical point2223 K, 16 MPa[5]
Heat of fusion2.33 kJ/mol
Heat of vaporization76.9 kJ/mol
Molar heat capacity29.6 J/(mol·K)
Atomic properties
Oxidation states−1, +1 (a strongly basic oxide)
ElectronegativityPauling scale: 0.82
Ionization energies
  • 1st: 418.8 kJ/mol
  • 2nd: 3052 kJ/mol
  • 3rd: 4420 kJ/mol
  • (more)
Atomic radiusempirical: 227 pm
Covalent radius203±12 pm
Van der Waals radius275 pm
Color lines in a spectral range
Spectral lines of potassium
Other properties
Natural occurrenceprimordial
Crystal structurebody-centered cubic (bcc) (cI2)
Lattice constant
Body-centered cubic crystal structure for potassium
a = 532.69 pm (at 20 °C)[4]
Thermal expansion77.37×10−6/K (at 20 °C)[4]
Thermal conductivity102.5 W/(m⋅K)
Electrical resistivity72 nΩ⋅m (at 20 °C)
Magnetic orderingparamagnetic[6]
Molar magnetic susceptibility+20.8×10−6 cm3/mol (298 K)[7]
Young's modulus3.53 GPa
Shear modulus1.3 GPa
Bulk modulus3.1 GPa
Speed of sound thin rod2000 m/s (at 20 °C)
Mohs hardness0.4
Brinell hardness0.363 MPa
CAS Number7440-09-7
History
Discovery and first isolationHumphry Davy (1807)
Symbol"K": from New Latin kalium
Isotopes of potassium
Main isotopes Decay
abun­dance half-life (t1/2) mode pro­duct
39K 93.3% stable
40K 0.0120% 1.248×109 y β 40Ca
ε 40Ar
β+ 40Ar
41K 6.73% stable
 Category: Potassium
| 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]

  1. ^ "Standard Atomic Weights: Potassium". CIAAW. 1979.
  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.
  3. ^ 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.
  4. ^ 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.
  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
  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.
  12. ^ Cite error: The named reference 1702Suspect was invoked but never defined (see the help page).
  13. ^ Greenwood, p. 73