The diagram shows the 'prototype' molecule, of the thermoplastic material polyethylene.Three different representations are given. In (a) the carbon and hydrogen atoms are shown at their relative radii and the covalent bonding between the carbon atoms is shown with the 109.5^o bond angle of the undeformed bond. The ball and stick model (b) reduces the atoms size to show the directional nature of the backbone carbon bonding and the allowed rotation of the hydrogen atoms about this direction. The linear representation (c) is concerned with the chemistry and bond type, showing the full use of all of the sp³ bonds of the carbon backbone atoms.

Solid polyethylene is composed of these macromolecules in a structure that may have both crystalline (organized) and amorphous (unorganized) regions in the same sample.

From: Askeland,
"The Science of Engineering Materials,"
PWS (1994)