POTASSIUM

introduction

Numéro atomique: 19
Groupe: 1 or I A
Poids atomique: 39.0983
Période: 4
Numero CAS: 7440-09-7

Classification

chalcogènes
Halogène
Gaz rare
lanthanides
actinides
Rare Earth Element
Groupe Platine Métal
Transuranium
Pas d'isotopes stables
Solide
Liquide
Gaz
Solide (prédit)

La description • Usages / Fonction

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

Propriétés physiques

Point de fusion:3*  63.5 °C = 336.65 K = 146.3 °F
Point d'ébullition:3* 759 °C = 1032.15 K = 1398.2 °F
sublimation point:3 
Triple point:3 
Point critique:3 1950 °C = 2223.15 K = 3542 °F 3
Densité:4  0.89 g/cm3

* - at 1 atm

Configuration de l'électron

Configuration de l'électron: [Ar] 4s1
Bloque: s
Plus haut niveau d'énergie occupés: 4
Électrons de valence: 1

Nombres quantiques:

n = 4
ℓ = 0
m = 0
ms = +½

Bonding

Électronégativité (échelle de Pauling):5 0.82
Electropositivity (échelle de Pauling): 3.18
Electron Affinity:6 0.50147 eV
oxydation États: +1
Fonction de travail:7 2.30 eV = 3.6846E-19 J

ionisation potentiel   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
ionisation potentiel   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
ionisation potentiel   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

Thermochimie

Chaleur spécifique: 0.757 J/g°C 9 = 29.597 J/mol°C = 0.181 cal/g°C = 7.074 cal/mol°C
Conductivité thermique: 102.4 (W/m)/K, 27°C 10
Température de fusion: 2.334 kJ/mol 11 = 59.7 J/g
Chaleur de vaporisation: 79.87 kJ/mol 12 = 2042.8 J/g
État de la matière Enthalpie de 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 Masse 14 Demi vie 14 Spin nucléaire 14 Énergie de liaison
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
Les valeurs marquées # ne sont pas purement dérivées des données expérimentales, mais au moins en partie des tendances systématiques. Spins avec de faibles arguments d'affectation sont entre parenthèses. 14

Réactions

Abondance

Terre - composés Source: halide salts or brines 15
Terre - Seawater: 399 mg/L 16
Terre -  Croûte:  20900 mg/kg = 2.09% 16
Terre -  Manteau:  0.2% 17
Terre -  lithosphère:  1.84% 18
Terre -  Hydrosphère:  0.04% 18
Terre -  Total:  135 ppm 19
Planète Mercure) -  Total:  22 ppm 19
Vénus -  Total:  150 ppm 19
chondrites - Total: 3500 (relative to 106 atoms of Si) 20
Corps humain - Total: 0.2% 21

composés

Information de sécurité


Fiche signalétique - ACI Alloys, Inc.

Pour plus d'informations

Liens externes:

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.