Carbon (from Latin: carbo "coal") is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table.[14] Carbon makes up only about 0.025 percent of Earth's crust.[15] Three isotopes occur naturally, 12C and 13C being stable, while 14C is a radionuclide, decaying with a half-life of about 5,730 years.[16] Carbon is one of the few elements known since antiquity.[17]
Carbon, 6C
Graphite-and-diamond-with-scale.jpg
Graphite (left) and diamond (right), two allotropes of carbon
Carbon
Allotropes
graphite, diamond and more (see Allotropes of carbon)
Appearance
graphite: black, metallic-looking
diamond: clear
Standard atomic weight Ar, std(C)
[12.0096, 12.0116] conventional: 12.011[1]
Carbon in the periodic table
boron ← carbon → nitrogen
Atomic number (Z)
6
Group
group 14 (carbon group)
Period
period 2
Block
p-block
Electron configuration
[He] 2s2 2p2
Electrons per shell
2, 4
Physical properties
Phase at STP
solid
Sublimation point
3915 K (3642 °C, 6588 °F)
Density (near r.t.)
amorphous: 1.8–2.1 g/cm3[2]
graphite: 2.267 g/cm3
diamond: 3.515 g/cm3
Triple point
4600 K, 10,800 kPa[3][4]
Heat of fusion
graphite: 117 kJ/mol
Molar heat capacity
graphite: 8.517 J/(mol·K)
diamond: 6.155 J/(mol·K)
Atomic properties
Oxidation states
−4, −3, −2, −1, 0, +1,[5] +2, +3,[6] +4[7] (a mildly acidic oxide)
Electronegativity
Pauling scale: 2.55
Ionization energies
1st: 1086.5 kJ/mol
2nd: 2352.6 kJ/mol
3rd: 4620.5 kJ/mol
(more)
Covalent radius
sp3: 77 pm
sp2: 73 pm
sp: 69 pm
Van der Waals radius
170 pm
Color lines in a spectral range
Spectral lines of carbon
Other properties
Natural occurrence
primordial
Crystal structure
graphite: simple hexagonalSimple hexagonal crystal structure for graphite: carbon
(black)
Crystal structure
diamond: face-centered diamond-cubicDiamond cubic crystal structure for diamond: carbon
(clear)
Speed of sound thin rod
diamond: 18,350 m/s (at 20 °C)
Thermal expansion
diamond: 0.8 µm/(m⋅K) (at 25 °C)[8]
Thermal conductivity
graphite: 119–165 W/(m⋅K)
diamond: 900–2300 W/(m⋅K)
Electrical resistivity
graphite: 7.837 µΩ⋅m[9]
Magnetic ordering
diamagnetic[10]
Molar magnetic susceptibility
diamond: −5.9×10−6 cm3/mol[11]
Young's modulus
diamond: 1050 GPa[8]
Shear modulus
diamond: 478 GPa[8]
Bulk modulus
diamond: 442 GPa[8]
Poisson ratio
diamond: 0.1[8]
Mohs hardness
graphite: 1–2
diamond: 10
CAS Number
atomic carbon: 7440-44-0
graphite: 7782-42-5
diamond: 7782-40-3
History
Discovery
Egyptians and Sumerians[12] (3750 BCE)
Recognized as an element by
Antoine Lavoisier[13] (1789)
Main isotopes of carbon
Isotope Abundance Half-life (t1/2) Decay mode Product
11C syn 20 min β+ 11B
12C 98.9% stable
13C 1.1% stable
14C trace 5730 y β− 14N
Category: Carbon
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Carbon is the 15th most abundant element in the Earth's crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. Carbon's abundance, its unique diversity of organic compounds, and its unusual ability to form polymers at the temperatures commonly encountered on Earth enables this element to serve as a common element of all known life. It is the second most abundant element in the human body by mass (about 18.5%) after oxygen.[18]
The atoms of carbon can bond together in diverse ways, resulting in various allotropes of carbon. Well-known allotropes include graphite, diamond, amorphous carbon and fullerenes. The physical properties of carbon vary widely with the allotropic form. For example, graphite is opaque and black while diamond is highly transparent. Graphite is soft enough to form a streak on paper (hence its name, from the Greek verb "γράφειν" which means "to write"), while diamond is the hardest naturally occurring material known. Graphite is a good electrical conductor while diamond has a low electrical conductivity. Under normal conditions, diamond, carbon nanotubes, and graphene have the highest thermal conductivities of all known materials. All carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form at standard temperature and pressure. They are chemically resistant and require high temperature to react even with oxygen.
The most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon monoxide and transition metal carbonyl complexes. The largest sources of inorganic carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peat, oil, and methane clathrates. Carbon forms a vast number of compounds, more than any other element, with almost ten million compounds described to date,[19] and yet that number is but a fraction of the number of theoretically possible compounds under standard conditions. For this reason, carbon has often been referred to as the "king of the elements".[20]
