Sample Chemical Structure

Chemical formula/structure of an ethylene molecule:

 or CH2=CH2 or C2H4

Chemical formula/structure of an ethylene monomer:

 or —(CH2-CH2)— or C2H4
The — symbols at the ends of the formula represent a monomer that is ready to react/connect to another monomer.

Chemical formula/structure of a growing polyethylene chain:

 
or —(CH2-CH2)x—

It should be pointed out that when the polyethylene chain is finished growing, two Hydrogen atoms are added to 'cap' (finish) the chain ends.