Signs of homologues and isomers.

ISOMERS – molecules or ions that have the same composition and molecular weight, but differ in the structure or arrangement of atoms in space.
HOMOLOGISTS (Greek homologos, from homos – general, and logos – word). Consonants, similar, proportionate, unambiguous.
Homologues are substances belonging to the same class, similar in composition, structure and properties, but differing by one or more CH2 groups (the CH2 group is called a homologous difference).
A homologous series is a series of substances arranged in increasing order of their molecular weights, similar in structure and chemical properties, where each member differs from the previous one by the CH2 group.