Tritiated water is a radioactive form of water where the usual hydrogen atoms are replaced with tritium.

Methane's four hydrogen atoms are replaced by two oxygen atoms to give carbon dioxide.

This geometry is often preserved when the hydrogen atoms are replaced by halogens or other simple groups.

By the symmetry of the hydrazine molecule, it does not matter which hydrogen atom is replaced.

The simplest member is toluene, in which a hydrogen atom of the benzene was replaced by a methyl group.

It may also be regarded as ammonia in which one or more hydrogen atoms have been replaced by an acid atom or radical.

It may be regarded as ammonia in which one hydrogen atom has been replaced by the radical phenyl.

The molecule structure resembles benzene, except that hydrogen atoms are replaced by chlorine.

This compound can be seen as a methane molecule, whose four hydrogen atoms are each replaced with a different halogen atom.

Each hydrogen atom can be replaced by a functional group.