Structure

Structure is normally defined as the organizational pattern or arrangement of parts that characterizes a thing. Chemists use this term to refer to the manner in which the atoms that compose a molecule of a specific compound are attached (bonded) to one another and oriented in space. This information is usually provided by a structural formula; examples of such formulas will be found throughout this text.
Three important aspects of structural formulas are:
Composition: The kinds and numbers of atoms that compose a molecule of a compound.
Constitution: The manner in which the component atoms of a molecule are bonded to each other. Different compounds having the same composition but different constitutions are called isomers. The prefix iso is from the Greek word for "the same or alike".
Configuration: The shape of a molecule in three-dimensional space. Isomers differing only in configuration are called stereoisomers.