K 19

Potassium (K)

alkali-metal

Period: 4 Group: 1 Block: s

Solid

Standard Atomic Weight

Electron configuration

[Ar] 4s¹

Melting point

63.38 °C (336.53 K)

Boiling point

758.85 °C (1032 K)

Density

890 kg/m³

Oxidation states

−1, +1

Electronegativity (Pauling)

0.82

Ionization energy (1st)

Discovery year

1807

Atomic radius

220 pm

Details

Name origin English: pot ash; symbol from Latin: kalium, (alkali).

Discovery country England

Discoverers Sir Humphrey Davy

Potassium is an alkali metal and a major rock-forming and biological element. It occurs naturally only in compounds, chiefly as K⁺ in salts, feldspars, micas, and clay minerals. The metal is highly electropositive, reacts vigorously with water, and is stored away from air and moisture. In living cells, potassium is the principal intracellular cation and is central to osmotic balance and electrical signaling.

It is one of the most reactive and electropositive of metals. Except for lithium, it is the lightest known metal. It is soft, easily cut with a knife, and is silvery in appearance immediately after a fresh surface is exposed. It rapidly oxidizes in air and must be preserved in a mineral oil such as kerosene.

As with other metals of the alkali group, it decomposes in water with the evolution of hydrogen. It catches fire spontaneously on water. Potassium and its salts impart a violet color to flames.

The name derives from the English "potash" or "pot ashes" because it is found in caustic potash (KOH). The symbol K derives from the Latin kalium via the Arabic qali for alkali. It was first isolated by the British chemist Humphry Davy in 1807 from electrolysis of potash (KOH).

Although potassium is the eighth most abundant element on earth and comprises about 2.1% of the earth's crust, it is a very reactive element and is never found free in nature. Metallic potassium was first isolated by Sir Humphry Davy in 1807 through the electrolysis of molten caustic potash (KOH). A few months after discovering potassium, Davy used the same method to isolate sodium. Potassium can be obtained from the minerals sylvite (KCl), carnallite (KCl·MgCl2·6H2O), langbeinite (K2Mg2(SO4)3) and polyhalite (K2Ca2Mg(SO4)4·2H2O). These minerals are often found in ancient lake and sea beds. Caustic potash, another important source of potassium, is primarily mined in Germany, New Mexico, California and Utah. Pure potassium is a soft, waxy metal that can be easily cut with a knife. It reacts with oxygen to form potassium superoxide (KO2) and with water to form potassium hydroxide (KOH), hydrogen gas and heat. Enough heat is produced to ignite the hydrogen gas. To prevent it from reacting with the oxygen and water in the air, samples of metallic potassium are usually stored submerged in mineral oil.

From the English word, potash - pot ashes; Latin kalium, Arab qali, alkali. Discovered in 1807 by Davy, who obtained it from caustic potash (KOH); this was the first metal isolated by electrolysis.

Read about Potassium on Wikipedia

Images

Properties

Physical

Atomic radius (empirical) 220 pm

Covalent radius 203 pm

Van der Waals radius 275 pm

Metallic radius 203 pm

Density

Molar volume 0.0453 L/mol

Phase at STP solid

Melting point 63.38 °C

Boiling point 758.85 °C

Thermal conductivity 79 W/(m·K)

Specific heat capacity 0.757 J/(g·K)

Molar heat capacity 29.6 J/(mol·K)

Crystal structure bcc

Chemical

Electronegativity (Pauling) 0.82

Electronegativity (Allen) 0.734

Electron affinity

Ionization energy (1st)

Ionization energy (2nd)

Ionization energy (3rd)

Ionization energy (4th)

Ionization energy (5th)

Oxidation states −1, +1

Valence electrons 1

Electron configuration

Electron configuration (semantic)

Thermodynamic

Critical point (temperature) 1950 °C

Critical point (pressure) 1.600000e+7 Pa

Heat of fusion 0.02414883 eV

Heat of vaporization 0.79701508 eV

Heat of sublimation 0.92449604 eV

Heat of atomization 0.92449604 eV

Atomization enthalpy

Nuclear

Stable isotopes 2

Discovery year 1807

Abundance

Abundance (Earth's crust) 2.090e+4 mg/kg

Abundance (ocean)

Reactivity

N/A

Crystal Structure

Lattice constant a 523 pm

Electronic Structure

Electrons per shell 2, 8, 8, 1

Identifiers

CAS number 7440-09-7

Term symbol

InChI InChI=1S/K

InChI Key ZLMJMSJWJFRBEC-UHFFFAOYSA-N

Electron Configuration Measured

Ion charge

Protons 19

Electrons 19

Charge Neutral

Configuration K: 4s¹

[Ar] 4s¹

1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹

Orbital diagram

↑↓

2/2

↑↓

2/2

↑↓

6/6

↑↓

2/2

↑↓

6/6

↑

1/2 1↑

Total electrons: 19 Unpaired: 1

Atomic model

Protons 19

Neutrons 20

Electrons 19

Mass number 39

Stability Stable

Isotopes change neutron count, mass, and stability — not the electron configuration of a neutral atom.

Schematic atomic model, not to scale.

Atomic Fingerprint

Emission / Absorption Spectrum

Emission Visible: 380–750 nm

Isotope Distribution

Mass number	Atomic mass (u)	Natural abundance	Half-life
39 Stable	38.9637064864 ± 0.0000000049	93.2581%	Stable
41 Stable	40.9618252579 ± 0.0000000041	6.7302%	Stable

Measured

Phase / State

Solid 25 °C (298.15 K)

Reason: 38.4 °C below melting point (63.38 °C)

Melting point 63.38 °C

Boiling point 758.85 °C

Below melting by 38.4 °C

0 K Current temperature: 25 °C 6000 K

Phase timeline

Schematic, not to scale

Solid

Liquid

Gas

Melting

Boiling

25°C

Solid

Liquid

Gas

Current

Phase transition points

Melting point Literature

63.38 °C

Boiling point Literature

758.85 °C

Current phase Calculated
Solid

Transition energies

Heat of fusion Literature

0.02414883 eV

Energy required to melt 1 mol at melting point

Heat of vaporization Literature

0.79701508 eV

Energy required to vaporize 1 mol at boiling point

Heat of sublimation Literature

0.92449604 eV

Energy required to sublime 1 mol at sublimation point

Density

Reference density Literature

890 kg/m³

At standard conditions

Current density Calculated

890 kg/m³

At standard conditions

Advanced

Critical point Literature

1950 °C

Atomic Spectra

Showing 10 of 22 Atomic Spectra. Sorted by ion charge (ascending).

Levels Holdings ?

Ion	Charge	Levels
41K I Isotope	0	8
40K I Isotope	0	3
39K I Isotope	0	123
K I	0	299
K II	+1	97
K III	+2	40
K IV	+3	38
K V	+4	40
K VI	+5	28
K VII	+6	81

NIST Levels Holdings →

19 K 39.0983

Potassium — Atomic Orbital Visualizer

[Ar]4s1

Energy levels 2 8 8 1

Oxidation states -1, +1

HOMO 4s n=4 · l=0 · m=0

Potassium — Atomic Orbital Visualizer Preview

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19 K 39.0983

Potassium — Crystal Structure Visualizer

Body-Centered Cubic · Pearson cI2

Experimental

Pearson cI2

Coord. № 8

Packing 68.000%

Potassium — Crystal Structure Visualizer Preview

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Ionic Radii

Charge	Coordination	Spin	Radius
+1	4	N/A	137 pm
+1	6	N/A	138 pm
+1	7	N/A	146 pm
+1	8	N/A	151 pm
+1	9	N/A	155 pm
+1	10	N/A	159 pm
+1	12	N/A	164 pm

Compounds

K+

39.098 u

39.964 u

42.961 u

41.962 u

37.969 u

38.964 u

43.962 u

44.961 u

K+

39.964 u

K+

37.969 u

K+

38.964 u

K+

42.961 u

K+

41.962 u

40.962 u

Isotopes (2)

Seventeen isotopes of potassium are known. Ordinary potassium is composed of three isotopes, one of which is 40°K (0.0118%), a radioactive isotope with a half-life of 1.28 x 109 years.

	Mass number	Atomic mass (u)	Natural abundance	Half-life	Decay mode
	39 Stable	38.9637064864 ± 0.0000000049	93.2581% ± 0.0044%	Stable	stable
	41 Stable	40.9618252579 ± 0.0000000041	6.7302% ± 0.0044%	Stable	stable

39 Stable

Atomic mass (u) 38.9637064864 ± 0.0000000049

Natural abundance 93.2581% ± 0.0044%

Half-life Stable

Decay mode

stable

41 Stable

Atomic mass (u) 40.9618252579 ± 0.0000000041

Natural abundance 6.7302% ± 0.0044%

Half-life Stable

Decay mode

stable

Spectral Lines

Showing 50 of 141 Spectral Lines. Only spectral lines with measured intensity are shown by default.

Wavelength (nm)	Intensity	Ion stage	Type	Transition	Accuracy	Source
693.8764 nm	20	K I	emission	3p6.4p 2P* → 3p6.6s 2S	Measured	NIST
691.10815 nm	19	K I	emission	3p6.4p 2P* → 3p6.6s 2S	Measured	NIST
404.41422 nm	18	K I	emission	3p6.4s 2S → 3p6.5p 2P*	Measured	NIST
404.72132 nm	17	K I	emission	3p6.4s 2S → 3p6.5p 2P*	Measured	NIST
580.17662 nm	17	K I	emission	3p6.4p 2P* → 3p6.7s 2S	Measured	NIST
583.18899 nm	17	K I	emission	3p6.4p 2P* → 3p6.5d 2D	Measured	NIST
578.23999 nm	16	K I	emission	3p6.4p 2P* → 3p6.7s 2S	Measured	NIST
581.21521 nm	15	K I	emission	3p6.4p 2P* → 3p6.5d 2D	Measured	NIST
535.95761 nm	14	K I	emission	3p6.4p 2P* → 3p6.6d 2D	Measured	NIST
533.96873 nm	13	K I	emission	3p6.4p 2P* → 3p6.8s 2S	Measured	NIST
511.225448 nm	12	K I	emission	3p6.4p 2P* → 3p6.7d 2D	Measured	NIST
532.32786 nm	12	K I	emission	3p6.4p 2P* → 3p6.8s 2S	Measured	NIST
534.29693 nm	12	K I	emission	3p6.4p 2P* → 3p6.6d 2D	Measured	NIST
693.62861 nm	12	K I	emission	3p6.4p 2P* → 3p6.4d 2D	Measured	NIST
696.46903 nm	12	K I	emission	3p6.4p 2P* → 3p6.4d 2D	Measured	NIST
464.23725 nm	11	K I	emission	3p6.4s 2S → 3p6.3d 2D	Measured	NIST
509.717137 nm	11	K I	emission	3p6.4p 2P* → 3p6.7d 2D	Measured	NIST
509.920005 nm	11	K I	emission	3p6.4p 2P* → 3p6.9s 2S	Measured	NIST
464.1875 nm	10	K I	emission	3p6.4s 2S → 3p6.3d 2D	Measured	NIST
496.503213 nm	10	K I	emission	3p6.4p 2P* → 3p6.8d 2D	Measured	NIST
508.423399 nm	10	K I	emission	3p6.4p 2P* → 3p6.9s 2S	Measured	NIST
482.924 nm	9	K II	emission	3p5.4s 3P* → 3p5.4p 3S	Measured	NIST
486.975897 nm	9	K I	emission	3p6.4p 2P* → 3p6.9d 2D	Measured	NIST
495.081801 nm	9	K I	emission	3p6.4p 2P* → 3p6.8d 2D	Measured	NIST
495.614802 nm	9	K I	emission	3p6.4p 2P* → 3p6.10s 2S	Measured	NIST
389.7896 nm	8	K II	emission	3p5.4s 3P* → 3p5.4p 1D	Measured	NIST
418.6232 nm	8	K II	emission	3p5.4s 3P* → 3p5.4p 3D	Measured	NIST
460.849 nm	8	K II	emission	3p5.4s 1P* → 3p5.4p 1D	Measured	NIST
480.43395 nm	8	K I	emission	3p6.4p 2P* → 3p6.10d 2D	Measured	NIST
485.609209 nm	8	K I	emission	3p6.4p 2P* → 3p6.9d 2D	Measured	NIST
486.348075 nm	8	K I	emission	3p6.4p 2P* → 3p6.11s 2S	Measured	NIST
500.564 nm	8	K II	emission	3p5.4s 3P* → 3p5.4p 3S	Measured	NIST
612.028 nm	8	K II	emission	3p5.3d 3F* → 3p5.4p 3D	Measured	NIST
381.7547 nm	7	K II	emission	3p5.4p 3D → 3p5.(2P<3/2>).5s 2[3/2]	Measured	NIST
400.122 nm	7	K II	emission	3p5.4s 3P* → 3p5.4p 3P	Measured	NIST
413.4705 nm	7	K II	emission	3p5.4s 3P* → 3p5.4p 3D	Measured	NIST
422.296 nm	7	K II	emission	3p5.4s 1P* → 3p5.4p 3P	Measured	NIST
422.566 nm	7	K II	emission	3p5.3d 3P* → 3p5.4p 1D	Measured	NIST
426.334 nm	7	K II	emission	3p5.4s 3P* → 3p5.4p 3D	Measured	NIST
430.498 nm	7	K II	emission	3p5.3d 3P* → 3p5.4p 1D	Measured	NIST
430.911 nm	7	K II	emission	3p5.4s 1P* → 3p5.4p 3P	Measured	NIST
438.816 nm	7	K II	emission	3p5.4s 1P* → 3p5.4p 1P	Measured	NIST
475.737719 nm	7	K I	emission	3p6.4p 2P* → 3p6.11d 2D	Measured	NIST
479.104132 nm	7	K I	emission	3p6.4p 2P* → 3p6.10d 2D	Measured	NIST
484.98645 nm	7	K I	emission	3p6.4p 2P* → 3p6.11s 2S	Measured	NIST
505.625 nm	7	K II	emission	3p5.3d 3P* → 3p5.4p 3S	Measured	NIST
630.728 nm	7	K II	emission	3p5.3d 3F* → 3p5.4p 3D	Measured	NIST
696.41712 nm	7	K I	emission	3p6.4p 2P* → 3p6.4d 2D	Measured	NIST
380.0162 nm	6	K II	emission	3p5.4p 3D → 3p5.(2P<3/2>).5s 2[3/2]	Measured	NIST
381.657 nm	6	K II	emission	3p5.4p 3P → 3p5.4d 3P*	Measured	NIST

Extended Properties

Covalent Radii (Extended)

Covalent radius (Pyykkö)

Covalent radius (Pyykkö, double)

Covalent radius (Bragg)

Van der Waals Radii

Bondi

Batsanov

Alvarez

UFF

MM3

Atomic & Metallic Radii

Atomic radius (Rahm)

Metallic radius (C12)

Numbering Scales

Mendeleev

Pettifor

Glawe

Electronegativity Scales

Ghosh

Miedema

Gunnarsson–Lundqvist

Robles–Bartolotti

Polarizability & Dispersion

Dipole polarizability

Dipole polarizability (unc.)

C₆

C₆ (Gould–Bučko)

Miedema Parameters

Miedema molar volume

Miedema electron density

Supply Risk & Economics

Production concentration

Relative supply risk

Reserve distribution

Political stability (top producer)

Political stability (top reserve)

Phase Transitions & Allotropes

Melting point	336.65 K
Boiling point	1032.15 K
Critical point (temperature)	2223.15 K
Critical point (pressure)	16 MPa

Oxidation State Categories

+1 main

−1 extended

Advanced Reference Data

Screening Constants (6)

n	Orbital	σ
1	s	0.5105
2	p	3.9728
2	s	5.9938
3	p	11.2744
3	s	10.3201
4	s	15.5048

Crystal Radii Detail (7)

Charge	CN	r_crystal (pm)
1	IV	151
1	VI	152
1	VII	160
1	VIII	165
1	IX	169
1	X	173
1	XII	178

Isotope Decay Modes (53)

Isotope	Mode	Intensity
31	3p	100%
32	p	—
33	p	—
34	p	—
35	B+	100%
35	B+p	0.4%
36	B+	100%
36	B+p	0%
36	B+A	0%
37	B+	100%

X‑ray Scattering Factors (503)

Energy (eV)	f₁	f₂
10	—	0.03426
10.1617	—	0.03529
10.3261	—	0.03635
10.4931	—	0.03744
10.6628	—	0.03856
10.8353	—	0.03972
11.0106	—	0.04091
11.1886	—	0.04214
11.3696	—	0.0434
11.5535	—	0.04471

Additional Data

Estimated Crustal Abundance

The estimated element abundance in the earth's crust.

2.09×104 milligrams per kilogram

References (1)

[5] Potassium https://education.jlab.org/itselemental/ele019.html

Estimated Oceanic Abundance

The estimated element abundance in the earth's oceans.

3.99×102 milligrams per liter

References (1)

[5] Potassium https://education.jlab.org/itselemental/ele019.html

Sources

Sources of this element.

The metal is the seventh most abundant and makes up about 2.4% by weight of the earth's crust. Most potassium minerals are insoluble and the metal is obtained from them only with great difficulty.

Certain minerals, however, such as sylvite, carnallite, langbeinite, and polyhalite are found in ancient lake and sea beds and form rather extensive deposits from which potassium and its salts can readily be obtained. Potash is mined in Germany, New Mexico, California, Utah, and elsewhere. Large deposits of potash, found at a depth of some 3000 ft in Saskatchewan, promise to be important in coming years.

Potassium is also found in the ocean, but is present only in relatively small amounts, compared to sodium.

References (1)

[6] Potassium https://periodic.lanl.gov/19.shtml

Production

Production of this element (from raw materials or other compounds containing the element).

Potassium is never found free in nature, but is obtained by electrolysis of the hydroxide, much in the same manner as prepared by Davy's first process. Thermal methods also are commonly used to produce potassium (such as by reduction of potassium compounds with CaC2, C, Si, or Na).

References (1)

[6] Potassium https://periodic.lanl.gov/19.shtml

References

(9)

1 PubChem

Data deposited in or computed by PubChem

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2 Atomic Mass Data Center (AMDC), International Atomic Energy Agency (IAEA)

The half-life and atomic mass data was provided by the Atomic Mass Data Center at the International Atomic Energy Agency.

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3 IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW)

Potassium

Element data are cited from the Atomic weights of the elements (an IUPAC Technical Report). The IUPAC periodic table of elements can be found at https://iupac.org/what-we-do/periodic-table-of-elements/. Additional information can be found within IUPAC publication doi:10.1515/pac-2015-0703 Copyright © 2020 International Union of Pure and Applied Chemistry.

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4 IUPAC Periodic Table of the Elements and Isotopes (IPTEI)

The information are cited from Pure Appl. Chem. 2018; 90(12): 1833-2092, https://doi.org/10.1515/pac-2015-0703.

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License note: Copyright (c) 2020 International Union of Pure and Applied Chemistry. The International Union of Pure and Applied Chemistry (IUPAC) contribution within Pubchem is provided under a CC-BY-NC-ND 4.0 license, unless otherwise stated.

5 Jefferson Lab, U.S. Department of Energy

Potassium

Thomas Jefferson National Accelerator Facility (Jefferson Lab) is one of 17 national laboratories funded by the U.S. Department of Energy. The lab's primary mission is to conduct basic research of the atom's nucleus using the lab's unique particle accelerator, known as the Continuous Electron Beam Accelerator Facility (CEBAF). For more information visit https://www.jlab.org/

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License note: Please see citation and linking information: https://education.jlab.org/faq/index.html

6 Los Alamos National Laboratory, U.S. Department of Energy

Potassium

The periodic table at the LANL (Los Alamos National Laboratory) contains basic element information together with the history, source, properties, use, handling and more. The provenance data may be found from the link under the source name.

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7 NIST Physical Measurement Laboratory

Potassium

The periodic table contains NIST's critically-evaluated data on atomic properties of the elements. The provenance data that include data for atomic spectroscopy, X-ray and gamma ray, radiation dosimetry, nuclear physics, and condensed matter physics may be found from the link under the source name. Ref: https://www.nist.gov/pml/atomic-spectra-database

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8 PubChem Elements

Potassium

This section provides all form of data related to element Potassium.

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9 PubChem Elements

Potassium

The element property data was retrieved from publications.

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Last updated: May 1, 2026