27
  Co  
58.933200
Cobalt

Name: Cobalt
Symbol: Co
Atomic Number: 27
Atomic Weight: 58.933200
Family: Transition Metals
CAS RN: 7440-48-4
Description: Tough silver-gray transition metal.
State (25C): Solid
Oxidation states: +2, +3

Molar Volume: 6.61 cm3/mole
Valence Electrons: 3d74s2

Boiling Point:  3143K, 2870C, 5198F
Melting Point:
1768K, 1495C, 2723F
Electrons Energy Level: 2, 8, 15, 2
Isotopes: 26 + 1 Stable
Heat of Vaporization: 376.5 kJ/mol
Heat of Fusion: 16.19 kJ/mol
Density: 8.9 g/cm3 @ 300K
Specific Heat: 0.42 J/gK
Atomic Radius: 1.67
Ionic Radius: 0.745
Electronegativity: 1.88 (Pauling); 1.7 (Allrod Rochow)
Vapor Pressure: 175 Pa @ 1495C

1s2 2s2p6 3s2p6d7 4s2

History

Cobalt compounds have been used for centuries to impart a rich blue color to glass, glazes, and ceramics.  Cobalt has been detected in Egyptian sculpture and Persian jewelry from the third millennium BC, in the ruins of Pompeii (destroyed AD 79), and in China dating from the Tang dynasty (AD 618–907) and the Ming dynasty (AD 1368–1644).  Cobalt glass ingots have been recovered from shipwrecks dating to the time of the Minoans.

cobalt.jpg (1355 bytes)

Alchemical Symbol, Cobalt

Swedish chemist Georg Brandt (1694–1768) is credited with isolating cobalt sometime between 1730 and 1737.  He was able to show that cobalt was the source of the blue color in glass, which previously had been attributed to the bismuth found with cobalt.

During the 19th century, cobalt blue was produced at the Norwegian Blaafarvevaerket (70-80 % of world production), led by the Prussian industrialist Benjamin Wegner.

In 1938, John Livingood and Glenn Seaaborg discovered cobalt-60.

The word cobalt is derived from the German kobalt, from kobold meaning "goblin", a term used for the ore of cobalt by miners, who thought it worthless and who found that it was poisonous and that it polluted and degraded other mined elements, mainly due to the arsenic and sulfur also found in the ore.

Cobalt's primary ores are cobaltite (CoAsS) and erythrite (Co3(AsO4)2).

Characteristics

Cobalt is ferromagnetic with atomic number 27.  The Curie temperature is of 1388oK with 1.6~1.7 Bohr magnetons per atom.  It is frequently associated with nickel, and both are characteristic ingredients of meteoric iron.  Mammals require small amounts of cobalt salts.  Cobalt-60, an artificially produced radioactive isotope of cobalt, is an important radioactive tracer and cancer treatment agent.  Cobalt has a relatively permeability two thirds that of iron.  Metallic cobalt commonly presents a mixture of two crystallographic structure.

1s2
2s2 2p6
3s2 3p6 3d7
4s2

Common oxidation states of cobalt include +2 and +3, though +1 is also seen.

Occurrence

Cobalt is not found as a free-metal and is generally found in the form of ores.   Cobalt is usually not mined alone, and tends to be produced as a by-product of nickel and copper mining activities.  The main ores of cobalt are cobaltite, erythrite, glaucodot, and skutterudite.  The world's major producers of cobalt are the Democratic Republic of the Congo, the People's Republic of China, Zaambia, Russia and Australia.  It is also found in Finland, Azerbaijan, Kazakhstan and Morocco.  It is also produced in the mines of Cobalt, Ontario, Canada as a byproduct of silver mining.

Applications

Use in Medicine

Cobalt-60 or 60Co is a radioactive metal that is used in radiotherapy.   It produces two gamma rays with energies of 1.17 MeV and 1.33 MeV.  The 60Co source is about 2 cm in diameter and as a result produces a geometric penumbra, making the edge of the radiation field fuzzy.  The metal has the unfortunate habit of producing a fine dust, causing problems with radiation protection.  The 60Co source is useful for about 5 years but even after this point is still very radioactive, and so cobalt machines have fallen from favor in the Western world where linacs are common.   Cobalt with alloying additions of chromium and molybdenum is widely used as a bio-medical implant material.

Co-60 is useful as a gamma ray source partially because it can be produced - in known quantity, and very large amounts - by simply exposing natural cobalt to neutrons in a reactor for a given time.

Cobalt in small amounts is essential to many living organisms, including humans.   Having 0.13 to 0.30 mg/kg of cobalt in soils markedly improves the health of grazing animals.  Cobalt is a central component of the vitamin cobalamin, or vitamin B12.

Compounds

There is a wide variety of cobalt compounds.  The +2 and +3 oxidation states are most prevalent, however cobalt (I) complexes are also fairly common.  Cobalt (II) salts form the red-pink [Co(OH2)6]2+ complex in aqueous solution.  Adding excess chloride will also change the colour from pink to blue, due to the formation of [CoCl4]2-.  Cobalt oxides are antiferromagnetic at low temperature: CoO (Neel temperature 291oK) and Co3O4 (Neel temperature: 40oK).

Isotopes

Naturally occurring cobalt is composed of 1 stable isotope, 59Co. 26 radioisotopes have been characterized with the most stable being 60Co with a half-life of 5.2713 years, 57Co with a half-life of 271.74 days, 56Co with a half-life of 77.233 days, and 58Co with a half-life of 70.86 days.   All of the remaining radioactive isotopes have half-lives that are less than 18 hours and the majority of these have half-lives that are less than 1 second.  This element also has 4 meta states, all of which have half-lives less than 15 minutes.

The isotopes of cobalt range in atomic weight from 47 amu (47Co) to 75 amu (75Co).   The primary decay mode before the most abundant stable isotope, 59Co, is electron capture and the primary mode after is beta decay.  The primary decay products before 59Co are element 26 (iron) isotopes and the primary products after are element 28 (nickel) isotopes.

atom.gif (700 bytes)

Isotope  
Atomic Mass
 
Half-Life
47Co 47.01149  
48Co 48.00176  
49Co 48.98972 <35 ns
50Co 49.98154 44 ms
51Co 50.97072 ~60 ms
52Co 51.96359 115 ms
53Co 52.954219 242 ms
54Co 53.9484596) 193.28 ms
55Co 54.9419990 17.53 hours
56Co 55.9398393 77.233 days
57Co 56.9362914 271.74 days
58Co 57.9357528 70.86 days
59Co 58.9331950 Stable
60Co 59.9338171 5.2713 years
61Co 60.9324758 1.650 hours
62Co 61.934051 1.50 minutes
63Co 62.933612 26.9 seconds
64Co 63.935810 0.30 seconds
65Co 64.936478 1.20 seconds
66Co 65.93976 0.18 seconds
67Co 66.94089 0.425 seconds
68Co 67.94487 0.199 seconds
69Co 68.94632 227 ms
70Co 69.9510 119 ms
71Co 70.9529 97 ms
72Co 71.95781 62 ms
73Co 72.96024 41 ms
74Co 73.96538 ~50 ms
75Co 74.96833 ~40 ms

Precautions

80px-Flammable.jpg (2186 bytes) Powdered cobalt in metal form is a fire hazard.  Cobalt compounds should be handled with care due to cobalt's slight toxicity.

Ingestion of 60Co will lead to incorporation of some cobalt into tissues, which is released very slowly. 

40px-Skull_and_crossbones.svg.jpg (1420 bytes) 60Co is a powerful gamma ray emitter and exposure to it is therefore a cancer risk. 

60Co is a risk factor in a nuclear confrontation because neutron emissions will convert 59Co into this isotope.  Some nuclear wepaons designs could intentionally increase the amount of 60Co dispersed as nuclear fallout   – this is sometimes called a dirty bomb or cobalt bomb, once predicted by a leading scientist as being capable of wiping out all life on earth.  The risk in the absence of a nuclear war comes from improper handling (or theft) of medical radiotherapeutic units. Nevertheless, the gamma radiation emitted from 60Co is used to kill bacteria on fruit and vegetables thus increasing their shelf life.  This process is referred to as irradiation.

atom.gif (700 bytes)

Cobalt Data

 

Atomic Structure

  • Atomic Radius: 1.67
  • Atomic Volume: 6.7cm3/mol
  • Covalent Radius: 1.16
  • Cross Section (Thermal Neutron Capture) Barns: 37.2
  • Crystal Structure: Hexagonal
  • Electron Configuration:
    1s2 2s2p6 3s2p6d7 4s2
  • Electrons per Energy Level: 2, 8, 15, 2
  • Ionic Radius: 0.745
  • Filling Orbital: 3d7
  • Number of Electrons (with no charge): 27
  • Number of Neutrons (most common/stable nuclide): 32
  • Number of Protons: 27
  • Oxidation States: 2, 3
  • Valence Electrons: 3d7 4s2

Chemical Properties

  • Electrochemical Equivalent: 1.0994 g/amp-hr
  • Electron Work Function: 5eV
  • Electronegativity: 1.88 (Pauling); 1.7 (Allrod Rochow)
  • Heat of Fusion: 16.19 kJ/mol
  • Incompatibilities:
    Strong oxidizers, ammonium nitrate
  • Ionization Potential
    • First: 7.86
    • Second: 17.06
    • Third: 33.5
  • Valence Electron Potential (-eV): 38.7

Physical Properties

  • Atomic Mass Average: 58.9332
  • Boiling Point: 3143K, 2870C, 5198F
  • Coefficient of Lineal Thermal Expansion/K-1: 13.36E-6
  • Conductivity
    Electrical: 0.172 106/cm
    Thermal: 1 W/cmK
  • Density: 8.9 g/cm3 @ 300K
  • Description:
    Tough silver-white transition metal.
  • Elastic Modulus:
    • Bulk: 181.5/GPa
    • Rigidity: 82/GPa
    • Youngs: 211/GPa
  • Enthalpy of Atomization: 26.8 kJ/mole @ 25C
  • Enthalpy of Fusion: 15.23 kJ/mole
  • Enthalpy of Vaporization: 382.4 kJ/mole
  • Flammablity Class: Non-combustible solid (except as dust)
  • Freezing Point: see melting point
  • Hardness Scale
    • Brinell: 700 MN m-2
    • Mohs: 5
    • Vickers: 1043 MN m-2
  • Heat of Vaporization: 376.5 kJ/mol
  • Melting Point: 1768K, 1495C, 2723F
  • Molar Volume: 6.61 cm3/mole
  • Optical Reflectivity: 67%
  • Physical State (at 20C & 1atm): Solid
  • Specific Heat: 0.42 J/gK
  • Vapor Pressure: 175 Pa @ 1495C

Regulatory / Health

  • CAS Number
    • 7440-48-4
  • RTECS: GF8750000
  • OSHA Permissible Exposure Limit (PEL)
    • TWA: 0.1 mg/m3
  • OSHA PEL Vacated 1989
    • TWA: 0.05 mg/m3
  • NIOSH Recommended Exposure Limit (REL)
    • TWA: 0.05 mg/m3
    • IDLH: 20 mg/m3
  • Routes of Exposure: Inhalation; Ingestion; Skin and/or eye contact
  • Target Organs: Skin, respiratory system
  • Levels In Humans:
    Note: this data represents naturally occuring levels of elements in the typical human, it DOES NOT represent recommended daily allowances.
    • Blood/mg dm-3: 0.0002-0.04
    • Bone/p.p.m: 0.01-0.04
    • Liver/p.p.m: 0.06-1.1
    • Muscle/p.p.m: 0.028-0.65
    • Daily Dietary Intake: 0.005-1.8 mg
    • Total Mass In Avg. 70kg human: 3 mg

Who / Where / When / How

  • Discoverer: George Brandt
  • Discovery Location: Stockholm Sweden
  • Discovery Year: 1735
  • Name Origin:
    German: kobalt or kobold (evil spirit); Greek: cobalos (mines).
  • Abundance:
    • Earth's Crust/p.p.m.: 20
    • Seawater/p.p.m.:
      • Atlantic Suface: N/A
      • Atlantic Deep: N/A
      • Pacific Surface: 0.0000069
      • Pacific Deep: 0.0000011
    • Atmosphere/p.p.m.: N/A
    • Sun (Relative to H=1E12): 79400
  • Sources:
    Occurs in compounds with arsenic, oxygen and sulfur as in cobaltine (CoAsS) and linneite (Co3S4). Annual world production is around 17,000 tons. Primary mining areas are in Zaire, Morocco, Sweden and Canada.
  • Uses:
    Used in many hard alloys; for magnets, ceramics and special glasses. Also used in permanent magnets, razor blades and catalitic converters. Cobalt-60 is used in cancer therapy.

Ionization Energy (eV): 7.881 eV
Estimated Crustal Abundance: 2.5101 milligrams per kilogram
Estimated Oceanic Abundance:
210-5 milligrams per liter

Transition Metals
Group 3
(IIIB)
4
(IVB)
5
(VB)
6
(VIB)
7
(VIIB)
8
(VIIIB)
9
(VIIIB)
10 (VIIIB) 11
(IB)
12
(IIB)
Period 4 21
Sc
44.95
22
Ti
47.86
23
V
50.94
24
Cr
51.99
25
Mn
54.93
26
Fe
55.84
27
Co
58.93
28
Ni
58.69
29
Cu
63.54
30
Zn
65.39
Period 5 39
Y
88.90
40
Zr
91.22
41
Nb
92.90
42
Mo
95.94
43
Tc
98.00
44
Ru
101.0
45
Rh
102.9
46
Pd
106.4
47
Ag
107.8
48
Cd
112.4
Period 6 57
La
138.9
72
Hf
178.4
73
Ta
180.9
74
W
183.8
75
Re
186.2
76
Os
190.2
77
Ir
192.2
78
Pt
195.0
79
Au
196.9
80
Hg
200.5
Period 7 89
Ac
227.0
104
Rf
261.0
105
Db
262.0
106
Sg
266.0
107
Bh
264.0
108
Hs
269.0
109
Mt
268.0
110
Ds
269.0
111
Rg
272.0
112
Uub
277.0