POTÁSSIO

Introdução

Número atômico: 19
Grupo: 1 or I A
Peso atômico: 39.0983
Período: 4
Número CAS: 7440-09-7

Classificação

Calcogênio
halogênio
Gás nobre
Lantanóides
Actinóide
Terra-rara
Platinum Metal Group
Transuranium
Não Isótopos Estáveis
Sólido
Líquido
Gás
Sólido (previsto)

Descrição • Usos / Função

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

Propriedades físicas

Ponto de fusão:3*  63.5 °C = 336.65 K = 146.3 °F
Ponto de ebulição:3* 759 °C = 1032.15 K = 1398.2 °F
Ponto de sublimação:3 
Ponto Triplo:3 
Ponto crítico:3 1950 °C = 2223.15 K = 3542 °F 3
Densidade:4  0.89 g/cm3

* - at 1 atm

Configuração Electron

Configuração Electron: [Ar] 4s1
Quadra: s
Mais alto nível de energia Ocupado: 4
Elétrons de valência: 1

Números quânticos:

n = 4
ℓ = 0
m = 0
ms = +½

Colagem

Eletronegatividade (escala Pauling):5 0.82
Electropositivity (escala Pauling): 3.18
Electron Affinity:6 0.50147 eV
oxidação Unidos: +1
Função no trabalho:7 2.30 eV = 3.6846E-19 J

potencial de ionização   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
potencial de ionização   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
potencial de ionização   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

Termoquímica

Calor específico: 0.757 J/g°C 9 = 29.597 J/mol°C = 0.181 cal/g°C = 7.074 cal/mol°C
Condutividade térmica: 102.4 (W/m)/K, 27°C 10
Calor de fusão: 2.334 kJ/mol 11 = 59.7 J/g
Calor da vaporização: 79.87 kJ/mol 12 = 2042.8 J/g
Estado da matéria Entalpia de formação (ΔHf°)13 entropia (S°)13 Gibbs Energia Livre (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

isótopos

nuclide Massa 14 Meia vida 14 spin nuclear 14 Energia de ligação
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) ESTÁVEL 3/2+ 334.38 MeV
40K 39.96399848(21) 1.248(3)E+9 a 4- 342.45 MeV
41K 40.96182576(21) ESTÁVEL 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
Os valores marcados # não são puramente derivado a partir de dados experimentais, mas, pelo menos, parcialmente a partir de tendências sistemáticas. Gira com argumentos de atribuição fracos estão entre parênteses. 14

reações

Abundância

Terra - Os compostos de origem: halide salts or brines 15
Terra - A água do mar: 399 mg/L 16
Terra -  crosta:  20900 mg/kg = 2.09% 16
Terra -  Manto:  0.2% 17
Terra -  litosfera:  1.84% 18
Terra -  Hidrosfera:  0.04% 18
Terra -  Total:  135 ppm 19
Planeta Mercúrio) -  Total:  22 ppm 19
Vênus -  Total:  150 ppm 19
condritos - Total: 3500 (relative to 106 atoms of Si) 20
Corpo humano - Total: 0.2% 21

compostos

Informação de Segurança


Material Safety Data Sheet - ACI Alloys, Inc.

Para maiores informações

Links externos:

Fontes

(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.