Hydrocarbons known as alkanes have carbon chains where all of the carbon-carbon bonds are single bonds. The number of hydrogens at each carbon depends on the position of that carbon in the chain.
The structures at the right show that singly bonded carbons
at the end of the chain are also bonded to three hydrogens
bonded to two other atoms are also bonded to two hydrogens.
bonded to three other atoms are also bonded to one hydrogen.
bonded to two other atoms are also bonded to two hydrogens.
bonded to three other atoms are also bonded to one hydrogen.
The hydrocarbons shown at the right each have the same number of hydrogens and carbons (four carbons and ten hydrogens) but the atom-to-atom bonding sequence is different. Such compounds are known as constitutional isomers.