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Potassium

From Wikipedia, the free encyclopedia

argon ← potassium → calcium
Na
↑
K
↓
Rb

19K

Periodic table

Appearance
silvery gray

Spectral lines of potassium
General properties
Name, symbol, number potassium, K, 19
Pronunciation /p??tæsi?m/ po-tas-ee-?m
Element category alkali metal
Group, period, block 1, 4, s
Standard atomic weight 39.0983(1)
Electron configuration [Ar] 4s1
Electrons per shell 2, 8, 8, 1 (Image)
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 nΩ·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 β− 1.311 40Ca
ε 1.505 40Ar
β+ 1.505 40Ar
41K 6.73% 41K is stable with 22 neutrons

v · d · e · r

Potassium ( /p??tæsi?m/ po-tas-ee-?m) is the chemical element with the 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.

Potassium and sodium are chemically very similar. For this reason it took a long time before their salts were 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 as 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 ion is 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 is found in especially high concentrations within plant cells, and in a mixed diet, it is mostly concentrated in fruits. The high concentration of potassium in plants, associated with comparatively low amounts of sodium there, historically resulted in potassium first being isolated from potash, the ashes of plants, giving the element its name. Heavy crop production rapidly depletes soils of potassium, and agricultural fertilizers consume 95% of global potassium chemical production.[4]