POTASSIUM (K) • Element 19 • Physical Properties/Chemical Properties • Description • Uses/Function • Isotopes • Thermochemistry • Reactions • Electron Configuration and Bonding

Discovered in 1807 by Davy, who obtained it from caustic potash (KOH); this was the first metal isolated by electrolysis. 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 1000 m 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. The greatest demand for potash has been in its use for fertilizers. Potassium is an essential constituent for plant growth and it is found in most soils. Potassium is never found free in nature, but is obtained by electrolysis of the hydroxide, much in the same manner as prepared by Davy. Thermal methods also are commonly used to produce potassium (such as by reduction of potassium compounds with CaC2, C, Si, or Na). 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 should be preserved in a mineral oil. 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. Twenty one isotopes, one of which is an isomer, of potassium are known. Ordinary potassium is composed of three isotopes, one of which is potassium-40 (0.0117%), a radioactive isotope with a halflife of 1.28 X 10^9 years. The radioactivity presents no appreciable hazard. An alloy of sodium and potassium (NaK) is used as a heat-transfer medium. Many potassium salts are of utmost importance, including the hydroxide, nitrate, carbonate, chloride, chlorate, bromide, iodide, cyanide, sulfate, chromate, and dichromate. Metallic potassium is available commercially for about $650/kg (98% purity) or $10/g (99.95% purity). 1

• "Potassium-40 is important in the potassium-argon radioactive decay method of dating ancient objects." 2

Melting Point:3* 63.5 °C = 336.65 K = 146.3 °F
Boiling Point:3* 759 °C = 1032.15 K = 1398.2 °F
Sublimation Point:3
Triple Point:3
Critical Point:3 1950 °C = 2223.15 K = 3542 °F 3
Density:4 0.89 g/cm3

* - at 1 atm

Electron Configuration

Electron Configuration: [Ar] 4s1
Block: s
Highest Occupied Energy Level: 4
Valence Electrons: 1

Quantum Numbers:

n = 4
ℓ = 0
mℓ = 0
ms = +½

Bonding

Electronegativity (Pauling scale):5 0.82
Electropositivity (Pauling scale): 3.18
Electron Affinity:6 0.50147 eV
Oxidation States: +1
Work Function:7 2.30 eV = 3.6846E-19 J

Ionization Potential	eV 8	kJ/mol
1	4.34066	418.8
2	31.63	3051.8
3	45.806	4419.6
4	60.91	5876.9
5	82.66	7975.5
6	99.4	9590.6

Ionization Potential	eV 8	kJ/mol
7	117.56	11342.8
8	154.88	14943.6
9	175.8174	16963.8
10	503.8	48609.3
11	564.7	54485.3
12	629.4	60727.9

Ionization Potential	eV 8	kJ/mol
13	714.6	68948.4
14	786.6	75895.3
15	861.1	83083.5
16	968	93397.8
17	1033.4	99707.9
18	4610.8	444874.5
19	4934.046	476063.0

Thermochemistry

Specific Heat: 0.757 J/g°C 9 = 29.597 J/mol°C = 0.181 cal/g°C = 7.074 cal/mol°C
Thermal Conductivity: 102.4 (W/m)/K, 27°C 10
Heat of Fusion: 2.334 kJ/mol 11 = 59.7 J/g
Heat of Vaporization: 79.87 kJ/mol 12 = 2042.8 J/g

State of Matter Enthalpy of Formation (ΔHf°)13 Entropy (S°)13 Gibbs Free Energy (ΔGf°)13

(kcal/mol) (kJ/mol) (cal/K) (J/K) (kcal/mol) (kJ/mol)

(s) 0 0 15.46 64.68464 0 0

(ℓ) 0.546 2.284464 17.08 71.46272 0.063 0.263592

(g) 21.3 89.1192 21.52 90.03968 14.5 60.668

Isotopes

Nuclide Mass 14 Half-Life 14 Nuclear Spin 14 Binding Energy

32K 32.02192(54)# 1+# 223.86 MeV
33K 33.00726(21)# <25 ns (3/2+)# 244.97 MeV
34K 33.99841(32)# <40 ns 1+# 261.42 MeV
35K 34.988010(21) 178(8) ms 3/2+ 278.81 MeV
36K 35.981292(8) 342(2) ms 2+ 293.40 MeV
37K 36.97337589(10) 1.226(7) s 3/2+ 308.92 MeV
38K 37.9690812(5) 7.636(18) min 3+ 320.72 MeV
39K 38.96370668(20) STABLE 3/2+ 334.38 MeV
40K 39.96399848(21) 1.248(3)E+9 a 4- 342.45 MeV
41K 40.96182576(21) STABLE 3/2+ 352.39 MeV
42K 41.96240281(24) 12.360(12) h 2- 359.53 MeV
43K 42.960716(10) 22.3(1) h 3/2+ 369.46 MeV
44K 43.96156(4) 22.13(19) min 2- 376.60 MeV
45K 44.960699(11) 17.3(6) min 3/2+ 385.60 MeV
46K 45.961977(17) 105(10) s 2(-) 392.74 MeV
47K 46.961678(9) 17.50(24) s 1/2+ 400.82 MeV
48K 47.965514(26) 6.8(2) s (2-) 405.16 MeV
49K 48.96745(8) 1.26(5) s (3/2+) 411.37 MeV
50K 49.97278(30) 472(4) ms (0-,1,2-) 414.78 MeV
51K 50.97638(54)# 365(5) ms 3/2+# 419.13 MeV
52K 51.98261(75)# 105(5) ms (2-)# 421.61 MeV
53K 52.98712(75)# 30(5) ms (3/2+)# 425.02 MeV
54K 53.99420(97)# 10(5) ms 2-# 426.57 MeV
55K 54.99971(107)# 3# ms 3/2+# 429.99 MeV
Values marked # are not purely derived from experimental data, but at least partly from systematic trends. Spins with weak assignment arguments are enclosed in parentheses. 14

Reactions

2 K (s) + 2 H2O (ℓ) → 2 KOH (aq) + H2 (g)

Abundance

Earth - Source Compounds: halide salts or brines 15
Earth - Seawater: 399 mg/L 16
Earth - Crust: 20900 mg/kg = 2.09% 16
Earth - Mantle: 0.2% 17
Earth - Lithosphere: 1.84% 18
Earth - Hydrosphere: 0.04% 18
Earth - Total: 135 ppm 19
Mercury - Total: 22 ppm 19
Venus - Total: 150 ppm 19
Chondrites - Total: 3500 (relative to 106 atoms of Si) 20
Human Body - Total: 0.2% 21

Compounds

potassium acetate
potassium adipate
potassium aluminate
potassium aluminium fluoride; potassium tetrafluoridoaluminate; potassium tetrafluoroaluminate
potassium azide
potassium benzoate
potassium bicarbonate
potassium bifluoride
potassium binoxalate
potassium bisulfate
potassium bitartrate; potassium hydrogen tartrate
potassium borohydride
potassium bromate
potassium bromide
potassium carbonate
potassium carbonate dihydrate
potassium chlorate
potassium chloride
potassium chlorochromate; potassium trioxochlorochromate; Péligot**s salt
potassium chromate
potassium cyanate
potassium cyanide
potassium dichromate
potassium dihydrogen phosphate
potassium dimethyldithiocarbamate
potassium ethoxide
potassium ferrate
potassium ferric(III) oxalate; potassium trioxalatoferrate (III); potassium ferrioxalate
potassium ferricyanide
potassium ferrocyanide

potassium ferrocyanide trihydrate
potassium fluoride
potassium fluoroborate
potassium formate
potassium hexachlororuthenate
potassium hexafluoroaluminate
potassium hexafluorophosphate
potassium hexafluorosilicate
potassium hexafluorotitanate
potassium hexafluorozirconate
potassium hydride
potassium hydrogen iodate; potassium biiodate
potassium hydrogen phthalate; KHP
potassium hydroxide
potassium hypochlorite
potassium iodate
potassium iodide
potassium lactate
potassium manganate(VI); potassium manganate
potassium metabisulfite
potassium metaphosphate
potassium metavanadate
potassium methoxide
potassium niobate
potassium nitrate
potassium nitrite
potassium oleate
potassium oxide
potassium perchlorate

potassium periodate
potassium permanganate
potassium peroxide
potassium peroxomonosulfate
potassium perrhenate
potassium perruthenate
potassium persulfate
potassium phosphate
potassium phosphate dibasic; potassium hydrogen phosphate
potassium phosphide
potassium propionate
potassium pyrophosphate
potassium pyrosulfate
potassium selenate
potassium selenide
potassium silicate
potassium sorbate
potassium stannate trihydrate
potassium sulfate
potassium sulfide
potassium superoxide
potassium tartrate
potassium telluride
potassium tellurite
potassium tetrachloropallidate; potassium palladium chloride
potassium tetrachloroplatinate(II); potassium chloroplatinite
potassium thiocyanate
potassium thiosulfate
potassium trifluoromethanesulfonate
potassium xanthogenate

Safety Information

Material Safety Data Sheet - ACI Alloys, Inc.

For More Information

External Links:

Sources

(1) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:24.
(2) - Whitten, Kenneth W., Davis, Raymond E., and Peck, M. Larry. General Chemistry 6th ed.; Saunders College Publishing: Orlando, FL, 2000; p 921.
(3) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:132.
(4) - Lide, David R. CRC Handbook of Chemistry and Physics, 84th ed.; CRC Press: Boca Raton, FL, 2002; p 4:39-4:96.
(5) - Dean, John A. Lange's Handbook of Chemistry, 11th ed.; McGraw-Hill Book Company: New York, NY, 1973; p 4:8-4:149.
(6) - Lide, David R. CRC Handbook of Chemistry and Physics, 84th ed.; CRC Press: Boca Raton, FL, 2002; p 10:147-10:148.
(7) - Speight, James. Lange's Handbook of Chemistry, 16th ed.; McGraw-Hill Professional: Boston, MA, 2004; p 1:132.
(8) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 10:178 - 10:180.
(9) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:133.
(10) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:193, 12:219-220.
(11) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:123-6:137.
(12) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:107-6:122.
(13) - Dean, John A. Lange's Handbook of Chemistry, 12th ed.; McGraw-Hill Book Company: New York, NY, 1979; p 9:4-9:94.
(14) - Atomic Mass Data Center. http://amdc.in2p3.fr/web/nubase_en.html (accessed July 14, 2009).
(15) - Silberberg, Martin S. Chemistry: The Molecular Nature of Matter and Change, 4th ed.; McGraw-Hill Higher Education: Boston, MA, 2006, p 965.
(16) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 14:17.
(17) - Silberberg, Martin S. Chemistry: The Molecular Nature of Matter and Change, 4th ed.; McGraw-Hill Higher Education: Boston, MA, 2006, p 962.
(18) - Silberberg, Martin S. Chemistry: The Molecular Nature of Matter and Change, 4th ed.; McGraw-Hill Higher Education: Boston, MA, 2006, p 964.
(19) - Morgan, John W. and Anders, Edward, Proc. Natl. Acad. Sci. USA 77, 6973-6977 (1980)
(20) - Brownlow, Arthur. Geochemistry; Prentice-Hall, Inc.: Englewood Cliffs, NJ, 1979, pp 15-16.
(21) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 7:17.

POTASSIUM

Introduction

Classification

Description • Uses/Function

Physical Properties