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THE CARBON ATOM

Carbon

is found in many different compounds. It is in the food you eat, the clothes you wear, the cosmetics you use and the gasoline that fuels your car. Carbon is the sixth most abundant element in the universe. In addition, carbon is a very special element because it plays a dominant role in the chemistry of life. Carbon, discovered in prehistory and was known to the ancients, who manufactured it by burning organic material making charcoal. There are four known allotopes of cabon: amorphous, graphite, diamond and fullerene. A new (fifth) allotrope of carbon was recently found. It is a spongy solid that is extremely lightweight and, unusually, attracted to magnets. The inventors of this new form of carbon -- a magnetic carbon nanofoam-- say it could may someday find medical applications (see review article from Nature)

Physical Properties of the Carbon Atom

Atomic Number 6
Atomic Mass Average: 12.011
Melting Point: 3823 K (3550°C or 6422°F)
Boiling Point: 4098 K (3825°C or 6917°F)
Density: 2.267g/cu.cm.
Velocity of sound [/m s-1]: 18350
Hardness Scale Mohs: 0.5
Stable Isomers (2)

Atomic Structure

The Carbon atom has six electrons, 4 of the electrons are in its valence shell (outershell). The circles in the diagram show energy levels - representing increasing distances from the nucleus.

This diagram is, however, a simplification and can be misleading. It gives the impression that the electrons are circling the nucleus in orbits like planets around the sun. Actually it is not possible to know exactly where the electrons are located (see below)

A better way to look at the carbon atom is by using an energy level graph shown at the right. Here we see carbon has six electrons represented by arrows (the direction of the arrow represents the electron spin) Two electrons are found in the 1s orbital close to the nucleus. The next two will go into the 2s orbital. The remaining ones will be in two separate 2p orbitals. This is because the p orbitals have the same energy and the electrons would rather be in separate orbitals.

The actual location of electrons in a carbon atom cannot be determined with certainty and the electrons appear to be 'smeared' into orbitals as shown below. These images were created using the java applet --Atomic and Molecular Orbitals from MIT. This java applet and other Molecular Orbitals applets can be found at the Chemistry Java Page.


2s	2px	2py

Isotopes

Isotopes are atoms which have the same atomic number but different mass numbers. They have the same number of protons but different numbers of neutrons.The number of neutrons in an atom can vary within small limits. For example, there are three kinds of carbon atom 12C, 13C and 14C. They all have the same number of protons, but the number of neutrons varies.

	protons	neutrons	mass number
carbon 12	6	6	12
carbon 13	6	7	13
carbon 14	6	8	14

These different types of carbon atoms are called isotopes. The fact that they have varying numbers of neutrons makes no difference to the chemical reactions of the carbon atom.

Uses of Carbon

Graphite combined with clays form the 'lead' used in pencils.
Diamond is used for decorative purposes, and also as drill bits.
Carbon added to iron makes steel.
Carbon is used for control rods in nuclear reactors.
Graphite carbon in a powdered, caked form is used as charcoal for cooking, artwork and other uses.
Charcoal pills are used in medicine in pill or powder form to adsorb toxins or poisons from the digestive system.

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