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# Potassium

Potassium,  19K
Potassium pearls (in paraffin oil, ~5 mm each)
General properties
Pronunciation
Appearancesilvery gray
Standard atomic weight (Ar, standard)Lua error in package.lua at line 80: module 'Module:Gapnum' not found.[1]
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
19
Groupgroup 1 (alkali metals)
Periodperiod 4
Blocks-block
Element category  alkali metal
Electron configuration[Ar] 4s1
Electrons per shell
2, 8, 8, 1
Physical properties
Phase at STPK: Solid
Melting point336.7 K ​(63.5 °C, ​146.3 °F)
Boiling point1032 K ​(759 °C, ​1398 °F)
Density (near r.t.)0.862 g/cm3
when liquid (at m.p.)0.828 g/cm3
Critical point2223 K, 16 MPa[2]
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)
Spectral lines of potassium
Other properties
Natural occurrenceK: Primordial
Crystal structurebody-centered cubic (bcc)
Speed of sound thin rod2000 m/s (at 20 °C)
Thermal expansion83.3 µm/(m·K) (at 25 °C)
Thermal conductivity102.5 W/(m·K)
Electrical resistivity72 nΩ·m (at 20 °C)
Magnetic orderingparamagnetic[3]
Magnetic susceptibility+20.8·10−6 cm3/mol (298 K)[4]
Young's modulus3.53 GPa
Shear modulus1.3 GPa
Bulk modulus3.1 GPa
Mohs hardness0.4
Brinell hardness0.363 MPa
CAS Number7440-09-7
History
Discovery and first isolationHumphry Davy (1807)
Main isotopes of potassium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct
39K 93.258% stable
40K 0.012% 1.248×109 y β 1.311 40Ca
ε 1.505 40Ar
β+ 1.505 40Ar
41K 6.730% stable
| references
Potassium metal

Potassium is a chemical element in the periodic table. It has the symbol K. This symbol is taken from the Latin word kalium. Potassium's atomic number is 19. It has 19 protons and electrons. Potassium is not found as an element in nature, because it is so reactive.

Potassium has two stable isotopes, with 20 or 22 neutrons. Its atomic mass is 39.098. The unstable isotope with 21 neutrons is one of the most common radioactive materials.

## Properties

### Physical properties

Potassium is a soft gray metal. It can be cut easily with a knife. Its melting point is 63 degrees Celsius (145.4 degrees Fahrenheit). It melts at a very low temperature. It is an alkali metal. It is the second lightest metal, after lithium.

### Chemical properties

Potassium reacts in many chemical reactions similar to sodium and other alkali metals. It tarnishes in air to produce a whitish oxidized layer on the surface. This is why it is stored in oil. It also reacts very fast with water, which is another reason for its storage in oil. The hydrogen produced during its reaction with water can burst into flames when a large amount of potassium is added to water. Potassium hydroxide is also produced. Potassium also burns in air easily, to make the peroxide or the superoxide.

### Chemical compounds

Potassium chloride in a flame

Potassium compounds are only in one oxidation state: +1. Potassium ions are colorless and similar to sodium ions. Potassium chloride can be used as a substitute for table salt. Potassium hydroxide is used in the electrolyte of alkaline cells. Most potassium compounds are nontoxic. If they are toxic, it is because of the anion. Potassium chromate is colored because of the chromate, not the potassium. Potassium chromate is toxic because of the chromate, not the potassium.

## Name

The word potassium comes from the word "potash". Potash is a mixture of potassium carbonate and potassium hydroxide that has been used for a very long time. In past centuries potash was made from ashes in pots. It is used to make fertilizer, soap, and glass.

## Occurrence

Potassium does not occur in nature because it is too reactive. It is found in minerals, though. It is extracted from them by electrolysis of potassium hydroxide or potassium chloride. The potassium hydroxide or potassium chloride has to be melted at a very high temperature.

## Uses

Potassium metal is used to absorb water from solvents. It is also used in some scientific instruments.

Potassium compounds are used in soap, fertilizer, explosives, and matches.

### Nutrition

Potassium ions are very important to organisms. That is why fertilizers have potassium compounds in them. The ions send messages from cells to other cells. It helps biological membranes depolarize. This means go from a negative to a positive electrical charge. This is needed for muscles to contract (get shorter and move things.) It is needed for the heart to beat (push blood through blood vessels.) If the potassium level in the blood is too high or too low it can cause death because the heart stops.[6] A few good sources of potassium are bananas, apricots and raisins.

## Safety

Potassium metal is very dangerous and can form an explosive coating if it is kept in air. It also reacts violently with water, spewing corrosive liquid. Potassium compounds are not normally dangerous, unless they contain a toxic anion like chromate or chlorate.

## References

1. Meija, J.; Coplen, T. B.; Berglund, M.; Brand, W.A.; De Bièvre, P.; Gröning, M.; Holden, N.E.; Irrgeher, J. et al. (2016). "Atomic weights of the elements 2013 (IUPAC Technical Report)". Pure and Applied Chemistry 88 (3): 265-91. .
2. Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 4.122. .
3. Magnetic susceptibility of the elements and inorganic compounds, in Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. .
4. Weast, Robert (1984). CRC, Handbook of Chemistry and Physics. Boca Raton, Florida: Chemical Rubber Company Publishing. pp. E110. .
5. "Potassium". Retrieved 13 October 2010.
6. Whelton, P.; He, J.; Cutler, J.; Brancati, F.; Appel, L.; Follmann, D.; Klag, M. (1997). "Effects of oral potassium on blood pressure. Meta-analysis of randomized controlled clinical trials." (in en).