BORO

Introdução

Número atômico: 5
Grupo: 13 or III A
Peso atômico: 10.811
Período: 2
Número CAS: 7440-42-8

Classificação

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

Descrição • Usos / Função

Boron compounds have been known for thousands of years, but the element was not discovered until 1808 by Sir Humphry Davy and by Gay-Lussac and Thenard. The element is not found free in nature, but occurs as orthoboric acid usually in certain volcanic spring waters and as borates in borax and colemanite. Ulexite, another boron mineral, is interesting as it is nature’s own version of “fiber optics.” Important sources of boron are the ores rasorite (kernite) and tincal (borax ore). Both of these ores are found in the Mojave Desert. Tincal is the most important source of boron from the Mojave. Extensive borax deposits are also found in Turkey. Boron exists naturally as 19.9% 10B isotope and 80.1% 11B isotope. Eleven isotopes of boron are known. High-purity crystalline boron may be prepared by the vapor phase reduction of boron trichloride or tribromide with hydrogen on electrically heated filaments. The impure, or amorphous, boron, a brownish-black powder, can be obtained by heating the trioxide with magnesium powder. Boron of 99.9999% purity has been produced and is available commercially. Elemental boron has an energy band gap of 1.50 to 1.56 eV, which is higher than that of either silicon or germanium. It has interesting optical characteristics, transmitting portions of the infrared, and is a poor conductor of electricity at room temperature, but a good conductor at high temperature. Amorphous boron is used in pyrotechnic flares to provide a distinctive green color, and in rockets as an igniter. By far the most commercially important boron compound in terms of dollar sales is Na2B4O7 · 5H2O. This pentahydrate is used in very large quantities in the manufacture of insulation fiberglass and sodium perborate bleach. Boric acid is also an important boron compound with major markets in textile fiberglass and in cellulose insulation as a flame retardant. Next in order of importance is borax (Na2B4O7 · 10H2O) which is used principally in laundry products. Use of borax as a mild antiseptic is minor in terms of dollars and tons. Boron compounds are also extensively used in the manufacture of borosilicate glasses. Other boron compounds show promise in treating arthritis. The isotope boron-10 is used as a control for nuclear reactors, as a shield for nuclear radiation, and in instruments used for detecting neutrons. Boron nitride has remarkable properties and can be used to make a material as hard as diamond. The nitride also behaves like an electrical insulator but conducts heat like a metal. It also has lubricating properties similar to graphite. The hydrides are easily oxidized with considerable energy liberation, and have been studied for use as rocket fuels. Demand is increasing for boron filaments, a high-strength, lightweight material chiefly employed for advanced aerospace structures. Boron is similar to carbon in that it has a capacity to form stable covalently bonded molecular networks. Carboranes, metalloboranes, phosphacarboranes, and other families comprise thousands of compounds. Crystalline boron (99%) costs about $8/g. Amorphous boron costs about $4/g. Elemental boron and the borates are not considered to be toxic, and they do not require special care in handling. However, some of the more exotic boron hydrogen compounds are definitely toxic and do require care. 1

• "metabolism of calcium, magnesium, hormones" 2
• "By doping silicon with an element having three valence electrons, the conductivity is also very much enhanced. Consider what happens when silicon is doped with boron. Some of the silicon atoms in the solid are replaced by boron atoms; but because each boron atom has only three valence electrons, one of the four bonds to each boron atom has only one electron in it. We can think if this as a vacancy or "hole" in the bonding orbital. An electron from a neighboring atomcan move in to occupy this hole. Then a hole would exist on the neighboring atom, and an electron from another atom can move into it. As a result of this movement, boron-doped silicon is an electrical conductor. Because a hole is an absence of an electron, it is essentially a positive charge. Boron-doped silicon is called a p-type semiconductor, because the charge is carried by positive holes. The semiconductor behavior of doped silicon also can be explained in molecular orbital terms." 3

Propriedades físicas

Ponto de fusão:4*  2075 °C = 2348.15 K = 3767 °F
Ponto de ebulição:4* 4000 °C = 4273.15 K = 7232 °F
Ponto de sublimação:4 
Ponto Triplo:4 
Ponto crítico:4 
Densidade:5  2.34 g/cm3

* - at 1 atm

Configuração Electron

Configuração Electron: [He] 2s2 2p1
Quadra: p
Mais alto nível de energia Ocupado: 2
Elétrons de valência: 3

Números quânticos:

n = 2
ℓ = 1
m = -1
ms = +½

Colagem

Eletronegatividade (escala Pauling):6 2.04
Electropositivity (escala Pauling): 1.96
Electron Affinity:7 0.279723 eV
oxidação Unidos: +3
Função no trabalho:8 4.75 eV = 7.6095E-19 J

potencial de ionização   eV 9  kJ/mol  
1 8.29803    800.6
potencial de ionização   eV 9  kJ/mol  
2 25.15484    2427.1
3 37.93064    3659.7
potencial de ionização   eV 9  kJ/mol  
4 259.37521    25025.9
5 340.2258    32826.8

Termoquímica

Calor específico: 1.026 J/g°C 10 = 11.092 J/mol°C = 0.245 cal/g°C = 2.651 cal/mol°C
Condutividade térmica: 27 (W/m)/K, 27°C 11
Calor de fusão: 50.2 kJ/mol 12 = 4643.4 J/g
Calor da vaporização: 489.7 kJ/mol 13 = 45296.5 J/g
Estado da matéria Entalpia de formação (ΔHf°)14 entropia (S°)14 Gibbs Energia Livre (ΔGf°)14
(kcal/mol) (kJ/mol) (cal/K) (J/K) (kcal/mol) (kJ/mol)
(s) 0 0 1.40 5.8576 0 0
(g) 134.5 562.748 36.65 153.3436 124.0 518.816

isótopos

nuclide Massa 15 Meia vida 15 spin nuclear 15 Energia de ligação
10B 10.0129370(4) ESTÁVEL 3+ 65.62 MeV
11B 11.0093054(4) ESTÁVEL 3/2- 76.49 MeV
12B 12.0143521(15) 20.20(2) ms 1+ 79.90 MeV
13B 13.0177802(12) 17.33(17) ms 3/2- 85.18 MeV
14B 14.025404(23) 12.5(5) ms 2- 85.80 MeV
15B 15.031103(24) 9.87(7) ms 3/2- 88.28 MeV
16B 16.03981(6) <190E-12 s [<0.1 MeV] 0- 88.90 MeV
17B 17.04699(18) 5.08(5) ms (3/2-) 90.45 MeV
18B 18.05617(86)# <26 ns (4-)# 89.21 MeV
19B 19.06373(43)# 2.92(13) ms (3/2-)# 90.76 MeV
6B 6.04681(75)# 0.92 MeV
7B 7.02992(8) 350(50)E-24 s [1.4(2) MeV] (3/2-) 24.74 MeV
8B 8.0246072(11) 770(3) ms 2+ 37.74 MeV
9B 9.0133288(11) 800(300)E-21 s [0.54(21) keV] 3/2- 56.34 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. 15

reações

Abundância

Terra - Os compostos de origem: oxides 17
Terra - A água do mar: 4.44 mg/L 18
Terra -  crosta:  10 mg/kg = 0.001% 18
Terra -  Total:  9.6 ppb 19
Planeta Mercúrio) -  Total:  0.11 ppb 19
Vênus -  Total:  10.0 ppb 19
condritos - Total: 6.2 (relative to 106 atoms of Si) 20
Corpo humano - Total: 0.00007% 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 4:6.
(2) - Whitten, Kenneth W., Davis, Raymond E., and Peck, M. Larry. General Chemistry 6th ed.; Saunders College Publishing: Orlando, FL, 2000; p 926.
(3) - Ebbing, Darrell D. General Chemistry 3rd ed.; Houghton Mifflin Company: Boston, MA, 1990; p 394.
(4) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:132.
(5) - Lide, David R. CRC Handbook of Chemistry and Physics, 84th ed.; CRC Press: Boca Raton, FL, 2002; p 4:39-4:96.
(6) - Dean, John A. Lange's Handbook of Chemistry, 11th ed.; McGraw-Hill Book Company: New York, NY, 1973; p 4:8-4:149.
(7) - Lide, David R. CRC Handbook of Chemistry and Physics, 84th ed.; CRC Press: Boca Raton, FL, 2002; p 10:147-10:148.
(8) - Speight, James. Lange's Handbook of Chemistry, 16th ed.; McGraw-Hill Professional: Boston, MA, 2004; p 1:132.
(9) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 10:178 - 10:180.
(10) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 4:133.
(11) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:193, 12:219-220.
(12) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:123-6:137.
(13) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; pp 6:107-6:122.
(14) - Dean, John A. Lange's Handbook of Chemistry, 12th ed.; McGraw-Hill Book Company: New York, NY, 1979; p 9:4-9:94.
(15) - Atomic Mass Data Center. http://amdc.in2p3.fr/web/nubase_en.html (accessed July 14, 2009).
(16) - Atkins, Jones, and Laverman. Chemical Principles 6th ed.; W.H. Freeman and Company: New York, NY, 2013; p F94.
(17) - Silberberg, Martin S. Chemistry: The Molecular Nature of Matter and Change, 4th ed.; McGraw-Hill Higher Education: Boston, MA, 2006, p 965.
(18) - Lide, David R. CRC Handbook of Chemistry and Physics, 83rd ed.; CRC Press: Boca Raton, FL, 2002; p 14:17.
(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.