(From the Latin carbo, coal) A nonmetallic chemical element found in many inorganic compounds and all organic compounds. It exists freely as pure carbon in diamond and graphite and as the basic element in coal, coke, charcoal, soot, etc. Carbon is also useful as a neutron moderator, as in a nuclear reactor.

Symbol: C
Atomic number: 6
Atomic weight: 12.0107
Density (at room temperature and pressure): 2.3 g/cc (graphite); 3.513 (diamond)
Melting point: 3,550°C
Boiling point: 4,827°C
Main valence: -4, +2, +4
Ground state electron configuration: [He]2s22p2

See also: carbon-14
Carbon
Symbol: C
Atomic Number: 6
Boiling Point: 5100 K
Melting Point: 3825 K
Density at 300 K: 2.26 g/cm3
Covalent radius: 0.77
Atomic radius: 0.91
Atomic volume: 5.30 cm3/mol
First ionization potential: 11.260 V
Specific heat capacity: 0.709 J g-1 K-1
Thermal conductivity: 80-230 W m-1 K-1
Electrical conductivity: 0.07 106 Ω-1 m-1
Heat of fusion: N/A
Heat of vaporization: -715 kJ/mol
Electronegativity: 2.55 (Pauling's)

Previous Boron---Nitrogen Next
To the Periodic Table

Carbon and Life

It is hard to overstate the importance of carbon; its unique capacity for forming multiple bonds and chains at low energies makes life as we know it possible, and justifies an entire major branch of chemistry - organic chemistry - dedicated to its compounds. In fact, most of the compounds known to science are carbon compounds, often called organic compounds because it was in the context of biochemistry that they were first studied in depth.

What makes carbon so special is that every carbon atom is eager to bond with as many as four other atoms. This makes it possible for long chains and rings to be formed out of them, together with other atoms - almost always hydrogen, often oxygen, sometimes nitrogen, sulfur or halides. The study of these is the basis of organic chemistry; the compounds carbon forms with metals are generally considered inorganic. Chains and rings are fundamental to the way carbon-based life forms - that is, all known life-forms - build themselves. Silicon is capable of forming the same sorts of bonds and structures, but opinion is divided on whether silicon-based life forms are a realistic prospect - in part because it needs higher energies to form them, and in part because whereas carbon dioxide (one of the main by-products of respiration, a process essential to all known life) is a gas and therefore easy to remove from the body, its counterpart silicon dioxide (silica) has an inconveniently high melting point, posing a serious waste disposal problem for any would-be silicon-based life form.

Fuel

Almost everything we use as fuel, whether in food or power stations, is also based on one kind of carbon-based chain or another; everything from natural gas through petrol and alcohol to oil to wax and plastic is composed of hydrocarbon chains of various lengths. As a general rule, the longer the chains and the more saturated they are (meaning every atom of carbon bonds to four other atoms), the less volatile and more viscous the substance will be, and the higher its evaporation temparature. This spread of evaporation temperatures makes it possible to separate the wide range of different hydrocarbons present in crude oil through a process known as fractional distillation, heating the oil to a range of temperatures in sequence and collecting the vapors released. The other big class of carbon-based fuel (used universally by plants and animals, but rarely by power stations) is the carbohydrate family - sugar molecules and the things you can make from them, like starch, cellulose and so on.

Elemental Carbon

Besides its millions of compounds, carbon also bonds with itself in different ways to form graphite, diamond, fullerenes and amorphous solids. Under certain conditions, it can also form white carbon - a transparent, birefringent material about which little else seems to be known.

In graphite, probably best known for its use in pencil 'lead' (for which purpose it is mixed with clay), the carbon is loosely bonded in crystalline layers which are able to slip over one another, so it is relatively soft and deposits itself readily on flat surfaces when drawn over them. It is used as a lubricant, in clay, and as an electrical conductor - one of the few solid, non-metallic conductors. Diamond, by contrast, is the hardest substance known to man; it has a dense, extremely stable crystalline structure, and conducts heat extraordinarily well but electricity hardly at all. Thanks to its hardness it has many industrial applications, while its high refractive index gives jewellery a sparkle which is hard to match.

Another form of elemental carbon, the fullerene, was not observed until 1985, although the possibility of its existence had been suggested as long ago as 1966. The most basic fullerene, (C60, the buckyball - short for buckminsterfullerene) has the form of a football - that's a soccer ball if you American, or a truncated icosahedron if you're a mathematician - a spherical network of hexagons and pentagons. To the middle of this, rings of hexagons can be added to make bigger fullerenes - anywhere from one ring (C70) to thousands, making tubes of anything up to a millimetre long. Tubes can also exist without the hemispherical caps at either end, but in which case they're technically not fullerene because they don't include the twelve pentagons necessary to bend a sheet of hexagons into a closed shape.

The discovery of fullerenes was greeted with a flurry of excitement from chemists, and a huge number of possible uses were suggested; many of these (for instance, the idea that it might be a handy lubricant, like tiny ball bearings) turned out to be quite impractical, but it retains promise as a superconductor, a possible drug delivery vector, and a component of scanning tunnelling microscopes - attaching to the metal tip to increase resolution. The tubes, meanwhile, have extraordinary tensile strength and conduct electricity smoothly along their hollow middle, suggesting applications in nanoscale electronics, and in the production of super-strong, light fibres and resilient new materials. Doubtless many ingenious uses for both the balls and the tubes still remain to be dreamt up.

Isotopes

Carbon exists in three naturally-occurring isotopes - carbon-12, carbon-13, and carbon-14; the numbers refer to their atomic weights. The different kinds of carbon have very similar (but not quite identical) chemical and mechanical properties; the main practical significance of the existence of different isotopes stems from the fact that carbon-14 is radioactive, with a half-life of a few thousand years. This is what makes carbon dating possible - C-14 is thought to be created by impacts from cosmic rays at around the same rate it disappears through radioactive decay, so the ratio of the isotopes in the environment should stay more or less constant. Living organisms constantly exchange carbon with their environment until the day they die - so if we find a skull with only half as much C-14 in it as we see in our environment, we can infer that its owner died one half-life of C-14 ago - that's about 5,600 years. The technique is extremely useful in archaeology, but it is hard to know quite how accurate it is - the assumption that C-14 levels in the atmosphere have remained approximately constant is a difficult one to test.

The Carbon Cycle

The carbon cycle is crucial to the way the Earth's ecosystem works: Plants absorb the carbon dioxide that makes up around 0.03% of our atmosphere and use the energy of sunlight to build sugar molecules from water and CO2, a process known as photosynthesis. The details of this are still not fully understood by scientists, although work continues apace; it is hoped that a fuller understanding of photosynthesis may one day allow us to create more efficient solar cells, among other things. When the plants are eaten by animals, or decomposed by fungi, or burnt, the stored energy and carbon are released back into the environment and the cycle begins again.

The release of the carbon back into the environment may not happen straight away - when a forest is buried by a landslide, for example, trapping the stored carbon beneath the earth. This sort of thing has happened often enough over the course of the Earth's history to build up large reserves of fossil fuel in the Earth's crust (coal, oil and gas), which we are steadily burning our way through to generate power.

Carbon Emissions

Ever since the Industrial Revolution, humankind's ever-growing use of carbon-based fuels has thrown the carbon cycle somewhat out of balance, resulting in a significant, steady growth in the levels of carbon dioxide in our atmosphere - by about 30% since the start of the last century. It is thought by most environmental scientists that this, together with the rise in more potent 'greenhouse gases' like methane and the chlorofluorocarbons, is probably going to lead to global warming, if it hasn't already started to do so. This is because, like a greenhouse, these gases are transparent to visible light, and to many of the other wavelengths present in sunlight, but reflect infrared; so the energy comes in largely unobstructed and heats the earth below, which then radiates it as infrared back to the upper atmosphere, where the CO2 bounces it back down to Earth again.

There remains some scientific doubt over the reality and importance of the Greenhouse Effect, but regrettably if it is a real problem then we need to act now to stave off its worst effects. These are likely to include the flooding of low-lying lands the world over; the shifting of prime growing belts a couple of hundred miles away from the equator; a dangerous reduction in biodiversity as environmental conditions change quicker than many animals and plants can adapt to them; and the freezing over of Europe as the Gulf Stream changes its course, taking its warming currents elsewhere.

Acknowledging the undesirability of most of these consequences, a hundred or so of the world's countries got together to agree on the Kyoto Protocol, an international mechanism for the reduction of carbon emissions. The future of this agreement (which most environmentalists feel doesn't go far enough to prevent most of the damage) is uncertain as the United States - having argued for and won many concessions in the protocol, mainly in favour of big business, and gone on to sign but not ratify the treaty - has now pulled out entirely, complaining that we still can't really be certain that inaction will lead to environmental catastrophe and that it would cost an awful lot of money to do anything about it, and also that it was unfair because it doesn't make the same demands of the world's poorer countries as it does of them. The world's top carbon-emitting countries are as follows:

Rank

Nation

Total 94 emission (x 1000 tonnes)

Tonnes per person

Population in 1994

Share of world total

Share of world pop

1

United States

1,387,256

5.32

260,762,406

22.38%

4.45%

2

China

828,436

0.70

1,183,480,000

13.36%

20.21%

3

Russia

440,979

2.99

147,484,615

7.11%

2.52%

4

Japan

303,267

2.43

124,801,235

4.89%

2.13%

5

India

236,448

0.26

909,415,385

3.81%

15.53%

6

Germany

220,000

2.70

81,481,481

3.55%

1.39%

7

United Kingdom

149,741

2.56

58,492,578

2.42%

1.00%

8

Canada

121,712

4.18

29,117,703

1.96%

0.50%

9

Ukraine

111,644

2.17

51,448,848

1.80%

0.88%

10

Italy

106,947

1.87

57,190,909

1.72%

0.98%

11

Mexico

97,694

1.06

92,164,151

1.58%

1.57%

12

Poland

92,416

2.41

38,346,888

1.49%

0.65%

13

South Korea

91,853

2.06

44,588,835

1.48%

0.76%

14

France

88,196

1.53

57,644,444

1.42%

0.98%

15

South Africa

85,488

2.11

40,515,640

1.38%

0.69%

16

Australia

75,912

4.25

17,861,647

1.22%

0.31%

17

North Korea

71,079

3.03

23,458,416

1.15%

0.40%

18

Iran

69,573

1.06

65,634,906

1.12%

1.12%

19

Indonesia

66,964

0.34

196,952,941

1.08%

3.36%

20

Kazakhstan

66,547

3.01

22,108,638

1.07%

0.38%


Rest of world

1,487,848

0.63

2,352,473,913

24.00%

40.18%


Total World

6,200,000

1.06

5,855,425,579

100.00%

100.00%

(Table appears at http://www.abc.net.au/science/earth/climate/cfossil.htm - originally from Carbon Dioxide Information Analysis Center, Online Trends: A Compendium of Data on Global Change)

The Periodic Table

Each chapter of Primo Levi's classic The Periodic Table is themed around a different chemical element, sometimes loosely, sometimes less so. In the final part he tells the story of a single atom of carbon, with far greater poetry and scientific detail than I could hope to replicate: How it is trapped for millions of years in a changeless bed of limestone, until chipped free with a pickaxe and delivered to a lime kiln, where the heat frees it as a carbon dioxide molecule; how it is blown back and forth on its escape, sucked up by a falcon, exhaled, dissolved and expelled from oceans and torrents, then blown freely on the wind once more until it happens to meet with a vine where it is built into a sugar molecule. It is then made into wine, drunk, digested, exhaled, photosynthesised again, eaten by a wood-worm, consumed by microbial decomposers, and breathed out again to fly three times around the world before coming to rest at last in 1960. The story is at once utterly arbitrary, and entirely true; carbon atoms pass along these sorts of paths in such unimaginably huge numbers that it simply could not fail to be so.


I used information from many of the nodes linked to here in the creation of this writeup. Other sources include the Encyclopædia Britannica and Eric Weisstein's World of Chemistry at http://scienceworld.wolfram.com/chemistry/

with thanks to esapersona, Siobhan, wrinkly, LadySun, Professor Pi, Tiefling and Impartial for their helpful advice and suggestions.

Diamond, graphite, buckminsterfullerene and relatives, carbon nanotubes (which come in countless varieties), activated carbon, and carbon ropes all have the same chemical formula--C. Carbon is unique in having such a vast array of solid forms. The reason it has this many forms is the same reason that it is the basis element of organic life: it is the smallest element with four valence electrons.

Since carbon is small, it forms strong bonds with other elements, including itself. The simple reason for this rule of chemistry is that the carbon nucleus holds its outer shell of electrons tightly since they are close to the nucleus. When it bonds with another atom, that atom's electrons are also held tightly to the carbon nucleus since they are close.

Since carbon has four valence electrons, it can bond with up to four other atoms (sharing one electron a piece). If it bonds with four other carbon atoms, then you have the basis for the diamond structure. Imagine four carbon atoms located symmetrically in 3-dimensional space around a central carbon atom. Those four atoms form a shape known as a tetrahedron. If you treat each of those four atoms as the center of another atomic tetrahedron, you will end up making the diamond crystal--eventually all the carbon atoms (except the ones on the edges of the crystal) will have four symmetric bonds around them. Interestingly, the silicon used to make computer chips is identical to diamond except silicon atoms replace the carbon atoms. Like carbon, silicon has four valence electrons. However, silicon isn't nearly as strong as diamond because...its outer electrons are an extra shell removed from the nucleus. By the way, when carbon (or silicon) bonds in this way, it is known as sp3 hybridization (because the spherical s orbital and the 3 dumbbell p orbitals merge into 4 symmetric tetrahedral orbitals).

In graphite, carbon only bonds with three other carbon atoms in a plane. This is sp2 hybridization--the s orbital merges with two p orbitals and the remaining p orbital is left intact. The three bonded carbon atoms form a symmetric triangle, as you probably would expect, around the center carbon atom. If you bond carbon atoms to those surrounding atoms in the same way, you'll form a hexagonal lattice known as a graphene sheet. Keep in mind this sheet is totally 2-dimensional. However, every carbon atom has the remaining p orbital sticking up. Those p orbitals are what allows two graphene sheets to bond together. A stack of graphene sheets is called graphite. The p-orbital bonds aren't that strong, so the sheets easily slide across eachother. That's why graphite can be used as a lubricant or a pencil "lead." Roll up graphene sheets and you get carbon nanotubes. These can have either a single sheet or many sheets and were only discovered in 1991 by a researcher Iijima at NEC.

Activated carbon is extremely important in filters (I have one on my sink at home). To make activated carbon, you take a source of carbon with lots of other junk in it, like peanut shells or charcoal, and you steam-heat it at very high temperature. All the other junk leaves, and you're left with a very porous, amorphous carbon solid. All those pores help trap gook (especially if the gook is carbon-based, like bacteria), giving you clean water with small dissolved minerals.

The most interesting forms of carbon are the fullerenes and related structures. These are gorgeous 3-d enclosed geometrical structures. Who would have thought that nature could create the soccer ball structure of buckminsterfullerene based solely on the simple electric force? And, by the way, that's all chemistry is--one atom interacting with another because of Coulomb's Law. Beautiful!

Fifth song of Tori Amos's Scarlet's Walk. Preceded by Strange and followed by Crazy. This story is loosely inspired by the events said to take place in the song.


 carbon-made found her at the 
 End of a chain
 "time to race" she said
 "race the downhill" 

She was thinner than I remembered. Tanned and drained by the desert. Drained of water, that is, not of energy. Not by far. Not yet.

"Scarlet!" she exclaimed as soon as she saw me, and looked me in the eye, grinning. "I'm so delighted to see you! It's been ages and ages!!!" Her face became more serious. "Hasn't it?"

"Uh-huh," I confirmed drowsily, weary with travel. She supported me, limbs aching, as I left the Greyhound and climbed into her pickup.

Carrie kept the conversation up all the way to her home - "Never thought I'd live in a trailer, hahaha," - while I murmured encouraging words and gave nods I hoped she could perceive through the air. It was only when we arrived at her place she asked me what had happened in my life lately.

"Not too great," I told her. "I just broke up with this guy... not that I'm shedding any tears over him." I tried very hard not to make my eyes twinkle.

She tutted and fussed me to bed, and I woke up feeling better than I had in a long time.

 Bear Claw
 Free Fall 
 a Gunner's View
 black
 and
 blue 
 shred
 in
 ribbons
 of
 lithium 

"It looks even better with snow," she explained as we gazed out over the summerly ski resort. "But, of course, then there are more people."

"It's lovely," I said. "It feels so real. This is like the original America."

"Lots of history here," Carrie mused. "Wounded Knee is just across the hill, so to speak."

"Have you ever been there?" I asked.

"No, never. Too painful."

 carbon-made
 only 
 wants 
 to 
 be 
 unmade

As I slowly regained strength, Carrie lost it. Her chatter became more infrequent and less predictable. She would jump from one unrelated topic to another without noticing the friction. One night I woke up to her sobbing.

"It's nothing," she insisted. "I just get like this sometimes."

I knew that, of course. I was still worried.

 Blade to
 ice it's 
 Double Diamond 
 time 

After I'd been there for a couple of weeks, Carrie started disappearing. Just like that, she would be gone, for hours. She'd return in various states: Sullen, apologetic, torn. She claimed she had some thinking to do.

We had our first big argument when she came back bleeding.

"I want you to see a doctor," I ordered.
"See him for me," I pleaded.
"No more meds," she replied.

 Get me Neil on the line 
 No i can't hold 
 have him read
 
 'Snow
 Glass
 Apples" 
 where
 nothing is 
 what 
 it 
 seems 

Although they weren't exactly what you would call friends, Neil and Carrie understood each other better than most people do. I phoned him up daily, begging for advice. "Yoga," he suggested one day. "Exercise," another. That's how he had combatted it, he claimed. He was perfectly normal now, he said.

"We would have destroyed one another," he confided.

 and keep 
 your eyes 
 on her 
 keep
 don't
 look away

In the end, I ended up guarding her as much as I was visiting her. "What are you up to?" I asked her with my mother's voice whenever the room went too quiet. "Where are you going?" I asked, like my father, if she even approached the door. After days of this, she told me to see a doctor.

 keep
 your eyes on
 her eyes
 on 
 her 
 horizon
 on her
 eyes
 on her
 horizon

Swallowing tears, I climbed into the safety of the bus. "I'm sorry," had been her parting words, were mine. "Keep in touch," she had said, "you know where to find me."

I knew I didn't.

Car"bon (kär"bon), n. [F. carbone, fr. L. carbo coal; cf. Skr. çrA to cook.] (Chem.)

An elementary substance, not metallic in its nature, which is present in all organic compounds. Atomic weight 11.97. Symbol C. it is combustible, and forms the base of lampblack and charcoal, and enters largely into mineral coals. In its pure crystallized state it constitutes the diamond, the hardest of known substances, occuring in monometric crystals like the octahedron, etc. Another modification is graphite, or blacklead, and in this it is soft, and occurs in hexagonal prisms or tables. When united with oxygen it forms carbon dioxide, commonly called carbonic acid, or carbonic oxide, according to the proportions of the oxygen; when united with hydrogen, it forms various compounds called hydrocarbons. Compare Diamond, and Graphite.

Carbon compounds, Compounds of carbon (Chem.), those compounds consisting largely of carbon, commonly produced by animals and plants, and hence called organic compounds, though their synthesis may be effected in many cases in the laboratory.

The formation of the compounds of carbon is not dependent upon the life process.
I. Remsen

--
Carbon dioxide, Carbon monoxide. (Chem.) See under Carbonic. --
Carbon light (Elec.), an extremely brilliant electric light produced by passing a galvanic current through two carbon points kept constantly with their apexes neary in contact. --
Carbon point (Elec.), a small cylinder or bit of gas carbon moved forward by clockwork so that, as it is burned away by the electric current, it shall constantly maintain its proper relation to the opposing point. --
Carbon tissue, paper coated with gelatine and pigment, used in the autotype process of photography. Abney. --
Gas carbon, a compact variety of carbon obtained as an incrustation on the interior of gas retorts, and used for the manufacture of the carbon rods of pencils for the voltaic, arc, and for the plates of voltaic batteries, etc.

 

© Webster 1913


Car"bon, n. (Elec.)

A carbon rod or pencil used in an arc lamp; also, a plate or piece of carbon used as one of the elements of a voltaic battery.

 

© Webster 1913

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