Carbon forms four bonds in its compounds
ethene
The first two structures at the right show that singly bonded carbon atoms
at the end of the chain are also bonded to three hydrogen atoms.
bonded to two other carbon atoms are also bonded to two hydrogen atoms.
bonded to three other carbon atoms are also bonded to one hydrogen atom.
at the end of the chain are also bonded to three hydrogen atoms.
bonded to two other carbon atoms are also bonded to two hydrogen atoms.
bonded to three other carbon atoms are also bonded to one hydrogen atom.
Note that the number of hydrogen atoms and carbon atoms in the branched and straight chain compounds at the right are the same, but their atom-to-atom bonding sequence is different. Such compounds are known as constitutional isomers (structural isomers).
Carbon atoms may also be joined by multiple bonds.
In ethene the carbon atoms share four electrons (double bond).
This is represented by two lines between the bonded atoms.
This is represented by two lines between the bonded atoms.
Compounds that have only single bonds are referred to as saturated because the maximum number of hydrogen atoms are attached to each carbon atom. Ethene is referred to as unsaturated because it has fewer hydrogen atoms than the maximum at each carbon atom due to the double bond.