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About Potassium

Potassium Bohr

At 2.4% by mass of the earth’s crust, potassium is the 7th most abundant element in the earth’s crust, present in seawater, most soils, and minerals such as orthoclase, sylvite, carnallite, kainite, and langbeinite. Elemental potassium is typical of the alkali metals: it is a waxy solid soft enough to be cut with a knife, initially silvery in appearance, but rapidly darkens when exposed to oxygen in the air. It is extremely reactive because of its high electropositivity and will explode violently in contact with water, quickly converting to potassium hydroxide and liberating hydrogen gas. Potassium is the second least dense element that is solid at room temperature (behind lithium), and it is one of only three elements (with sodium and lithium) capable of floating on hydrocarbon-based mineral oil. Though potassium is nontoxic, it is classified as a hazardous material because of its dangerous reaction with water. Additionally, naturally occurring potassium is composed of three isotopes, two stable and one radioactive, and as such it is the most common radioactive element present in the human body.

For centuries prior to the element’s discovery, humans had used potash (potassium carbonate) in glass, soaps, and other applications, obtaining the compound by leaching wood ashes. In 1807, Sir Humphry Davy isolated metallic potassium from molten potassium hydroxide (caustic potash) using electrolysis. The element derives its name from potash and its elemental symbol “K” from the neo-Latin kalium and the Arabic al-qalyah or qali, meaning “alkali.” Currently, pure potassium metal is often produced in a similar electrolytic reaction of sodium metal and potassium chloride. Potassium compounds such as potassium chloride (often referred to as potash, muriate of potash, or MOP in the mineral industry), hydroxide, nitrate, carbonate, chloride, bromide, iodide, and sulfate are abundant and easily extracted from deposits in ancient lakes and seabeds, making them extremely commercially viable for industrial use. These compounds are highly soluble and are components of many soaps and detergents, glass and ceramic glazes, stains, and dyes. Compounds like potassium nitrate are used in gunpowder and pyrotechnics to produce the violet color in fireworks. High purity potassium compounds have numerous pharmacological, medical, and electronics applications. Sodium and potassium alloys are useful as heat transfer mediums, dessicants, reducing agents, and can be used in nuclear reactors.

Potassium is essential to life: the uptake of potassium ions is one of the key mechanisms of the human body and as such, compounds are important dietary components and can be used in food additives such as baking powder (potassium sodium tartrate) and low-sodium salt substitutes. Plants utilize soil-based potassium as a nutrient, and one of the main commercial uses of potassium compounds such as chloride, sulfate, and nitrate is in the production of fertilizers.

Additionally, experiments with potassium have shed light on several potentially useful applications for the element in the field of high technology. Potassium-ion batteries are an experimental design based on lithium-ion technology that substitute ions of potassium for those of lithium and have shown to retain charge after nearly 40 times more cycles than a similar lithium-ion model. Researchers have constructed a negative temperature system by cooling potassium gas to one billionth of a degree below absolute zero, a highly unusual achievement that could allow for further study of quantum effects in practical applications such as superconductivity.

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High Purity (99.999%) Potassium (K) Sputtering Target High purity potassium compounds have numerous pharmacological, medical, and electronics applications. High Purity (99.999%) Potassium Oxide (K2O) PowderImportant compounds include the chloride (often referred to as potash, muriate of potash, or MOP in the mineral industry), hydroxide, nitrate, carbonate, chloride, bromide, iodide, and sulfate. Lower purity compounds are used in pyrotechnics for its violet color on ignition and in glass and ceramic glazes to produce this color. Potassium is also used as a nutrient in plant growth. Potassium is available as metal and compounds with purities from 99% to 99.999% (ACS grade to ultra-high purity). Elemental or metallic forms include pellets, wire and granules for evaporation source material purposes. Potassium oxide is available in powder and dense pellet form for such uses as optical coating and thin film applications. Oxides tend to be insoluble. Potassium fluoride is another insoluble form for uses in which oxygen is undesirable such as metallurgy, chemical and physical vapor deposition and in some optical coatings. Potassium is available in soluble forms including chlorides, nitrates and acetates. These compounds are also manufactured as solutions at specified stoichiometries.

Potassium Properties

Potassium(K) atomic and molecular weight, atomic number and elemental symbolPotassium is a Block S, Group 1, Period 4 element. The number of electrons in each of Potassium's shells is 2, 8, 8, 1 and its electron configuration is [Ar] 4s1. The potassium atom has a radius of 227.2 pm and its Van der Waals radius is 275 pm. In its elemental form, CAS 7440-09-7, potassium has a silvery gray appearance. Potassium is the seventh most abundant element on earth. Elemental Potassium It is one of the most reactive and electropositive of all metals and rapidly oxidizes. Potassium Bohr Model As with other metals of the alkali group, the metal decomposes in water with the evolution of hydrogen. Since potassium reacts violently with water, it only occurs in nature in ionic salts. Potassium was first discovered by Sir Humphrey Davy in 1807. The origin of the element name comes from the English word 'potash' meaning pot ashes and the Arabic word 'qali' which means alkali. The symbol K originates from the Latin word 'kalium'. Potassium information, including technical data, safety data, high purity properties, research, applications and other useful facts are discussed below. Scientific facts such as the atomic structure, ionization energy, abundance on earth, conductivity and thermal properties are also included.

Symbol: K
Atomic Number: 19
Atomic Weight: 39.0983
Element Category: alkali metal
Group, Period, Block: 1, 4, s
Color: silvery white
Other Names: Kalium, Potássio, Draslík, Kalij
Melting Point: 63.5 °C, 146.3 °F, 336.65 K
Boiling Point: 759 °C, 1398.2 °F, 1032.15 K
Density: 0.862 g·cm3
Liquid Density @ Melting Point: 0.828 g·cm3
Density @ 20°C: 0.862 g/cm3
Density of Solid: 856 kg·m3
Specific Heat: 0.753 @20°C J(/g·mol)
Superconductivity Temperature: N/A
Triple Point: N/A
Critical Point: 2223 K, 16 MPa
Heat of Fusion (kJ·mol-1): 2.4
Heat of Vaporization (kJ·mol-1): 79.1
Heat of Atomization (kJ·mol-1): 90.14
Thermal Conductivity: 102.5 W·m-1·K-1
Thermal Expansion: (25 °C) 83.3 µm/(m·K)
Electrical Resistivity: (20 °C) 72 nΩ·m
Tensile Strength: N/A
Molar Heat Capacity: 29.6 J·mol-1·K-1
Young's Modulus: 3.53 GPa
Shear Modulus: 1.3 GPa
Bulk Modulus: 3.1 GPa
Poisson Ratio: N/A
Mohs Hardness: 0.4
Vickers Hardness: N/A
Brinell Hardness: 0.363 MPa
Speed of Sound: (20 °C) 2000 m·s-1
Pauling Electronegativity: 0.82
Sanderson Electronegativity: 0.45
Allred Rochow Electronegativity: 0.91
Mulliken-Jaffe Electronegativity: 0.73 (s orbital)
Allen Electronegativity: 0.734
Pauling Electropositivity: 3.18
Reflectivity (%): 5000 kg·m-3
Refractive Index: N/A
Electrons: 19
Protons: 19
Neutrons: 20
Electron Configuration: [Ar] 4s1
Atomic Radius: 227 pm
Atomic Radius,
non-bonded (Å):
Covalent Radius: 203 ±12 pm
Covalent Radius (Å): 2
Van der Waals Radius: 275 pm
Oxidation States: 1 (strongly basic oxide)
Phase: Solid
Crystal Structure: body-centered cubic
Magnetic Ordering: paramagnetic
Electron Affinity (kJ·mol-1) 48.367
1st Ionization Energy: 418.81 kJ·mol-1
2nd Ionization Energy: 3051.85 kJ·mol-1
3rd Ionization Energy: 4419.64 kJ·mol-1
CAS Number: 7440-09-7 
EC Number: N/A
MDL Number: MFCD00133776
Beilstein Number: N/A
SMILES Identifier: [K]
InChI Identifier: InChI=1S/K
PubChem CID: 5462222
ChemSpider ID: 4575326
Earth - Total: 135 ppm
Mercury - Total: 22 ppm
Venus - Total: 150 ppm
Earth - Seawater (Oceans), ppb by weight: 416000
Earth - Seawater (Oceans), ppb by atoms: 65800
Earth -  Crust (Crustal Rocks), ppb by weight: 15000000
Earth -  Crust (Crustal Rocks), ppb by atoms: 7800000
Sun - Total, ppb by weight: 4000
Sun - Total, ppb by atoms: 100
Stream, ppb by weight: 2300
Stream, ppb by atoms: 59
Meterorite (Carbonaceous), ppb by weight: 710000
Meterorite (Carbonaceous), ppb by atoms: 370000
Typical Human Body, ppb by weight: 2000000
Typical Human Body, ppb by atom: 320000
Universe, ppb by weight: 3000
Universe, ppb by atom: 100
Discovered By: Humphry Davy
Discovery Date: 1807
First Isolation: Humphry Davy (1807)

Health, Safety & Transportation Information for Potassium

Potassium is not toxic in its elemental form; however, safety data for its compounds can vary widely depending on the form. For potential hazard information, toxicity, and road, sea and air transportation limitations, such as DOT Hazard Class, DOT Number, EU Number, NFPA Health rating and RTECS Class, please see the specific material or compound referenced in the Products tab. The below information applies to elemental (metallic) Potassium.

Safety Data
Material Safety Data Sheet MSDS
Signal Word Danger
Hazard Statements H260-H314
Hazard Codes F,C
Risk Codes 14/15-34
Safety Precautions 8-43-45
RTECS Number N/A
Transport Information UN 2257 4.3/PG 1
WGK Germany 1
Globally Harmonized System of
Classification and Labelling (GHS)
Corrosion-Corrosive to metals Flame-Flammables

Potassium Isotopes

Potassium (K) has 25 isotopes ranging from 32K to 56K. Three of these occur naturally: 39K (93.3%), 41K (6.7%), and 40K (0.012%).

Nuclide Isotopic Mass Half-Life Mode of Decay Nuclear Spin Magnetic Moment Binding Energy (MeV) Natural Abundance
(% by atom)
32K 32.02192(54)# Unknown p to 31Ar 1+# N/A 217.64 -
33K 33.00726(21)# <25 ns p to 32Ar (3/2+)# N/A 238.76 -
34K 33.99841(32)# <40 ns p to 33Ar 1+# N/A 255.22 -
35K 34.988010(21) 178(8) ms ß- to 35Ar; ß- + p to 33Cl 3/2+ N/A 272.62 -
36K 35.981292(8) 342(2) ms ß- to 36Ar; ß- + p to 35Cl; ß- + a to 32S 2+ N/A 287.22 -
37K 36.97337589(10) 1.226(7) s EC to 37Ar 3/2+ 0.2032 302.75 -
38K 37.9690812(5) 7.636(18) min EC to 38Ar 3+ 1.37 314.55 -
39K 38.96370668(20) STABLE - 3/2+ 0.3914658 328.22 93.2581
40K 39.96399848(21) 1.248(3)E+9 y EC to 40Ar 4- -1.298099 336.3 0.0117
41K 40.96182576(21) STABLE - 3/2+ 0.2148699 346.24 6.7302
42K 41.96240281(24) 12.360(12) h ß- to 42Ca 2- -1.1425 353.39 -
43K 42.960716(10) 22.3(1) h ß- to 43Ca 3/2+ 0.163 363.33 -
44K 43.96156(4) 22.13(19) min ß- to 44Ca 2- -0.856 370.48 -
45K 44.960699(11) 17.3(6) min ß- to 45Ca 3/2+ 0.1734 379.49 -
46K 45.961977(17) 105(10) s ß- to 46Ca 2(-) -1.05 386.63 -
47K 46.961678(9) 17.50(24) s ß- to 47Ca 1/2+ 1.93 394.71 -
48K 47.965514(26) 6.8(2) s ß- to 48Ca; ß- + n to 47Ca (2-) N/A 399.07 -
49K 48.96745(8) 1.26(5) s ß- to 49Ca; ß- + n to 48Ca (3/2+) N/A 405.28 -
50K 49.97278(30) 472(4) ms ß- to 50Ca; ß- + n to 49Ca (0-,1,2-) N/A 408.7 -
51K 50.97638(54)# 365(5) ms ß- to 51Ca; ß- + n to 50Ca 3/2+# N/A 413.05 -
52K 51.98261(75)# 105(5) ms ß- + n to 51Ca; ß- + 2n to 50Ca; ß- to 52Ca (2-)# N/A 415.54 -
53K 52.98712(75)# 30(5) ms ß- + n to 52Ca; ß- + 2n to 51Ca; ß- to 53Ca (3/2+)# N/A 418.96 -
54K 53.99420(97)# 10(5) ms ß- to 54Ca; ß- + n to 53Ca 2-# N/A 420.52 -
55K 54.99971(107)# 3# ms ß- to 55Ca; ß- + n to 54Ca 3/2+# N/A 423.94 -
56K 56 Unknown Unknown N/A N/A N/A -