Carbon makes four bonds

0:00Carbon forms chains, branched chains and rings. Why can it make so many compounds?

0:07A carbon atom has four valence electrons, the electrons in its outer shell.

0:13Each one pairs with an electron from another atom. A shared pair is a covalent bond.

0:20Each pair is drawn as a line. Four bonds to hydrogen make methane, C H 4.

0:27Carbon can also bond to carbon. Two carbons make ethane, C 2 H 6.

0:34Three carbons in a chain make propane, C 3 H 8.

0:39Every carbon still has four bonds. Count them on the middle carbon: one, two, three, four.

0:48These are structural formulas: they show every atom and every bond.

0:53A condensed formula lists each carbon with its hydrogens. Propane is C H 3, C H 2, C H 3.

1:03A skeletal formula draws the carbon chain as lines. Each end or corner is a carbon, and hydrogens on carbon are left out.

1:13Methane has no chain, so it is still written C H 4.

1:18Structural formulas are flat, but bonds are electron pairs that repel, so they spread as far apart as possible.

1:26Four single bonds point to the corners of a triangular pyramid: a tetrahedral shape, 109.5 degrees apart.

1:35A double bond is two shared pairs. In ethene, each carbon is trigonal planar: flat, about 120 degrees apart.

1:45A triple bond is three shared pairs. In ethyne, each carbon is linear: 180 degrees apart.

1:53Single, double or triple, carbon makes four bonds because it has four valence electrons.