Ethylene (or Ethene) is a two-carbon alkene. Its chemical formula is CH2CH2 (or C2H4), and its structure is as shown here:
In a three-dimensional model, this same ethylene molecule might look like this:
Ethylene is involved with the process of fruit ripening. This is why apples (which produce large amounts of ethylene during ripening) will speed the ripening process of any other fruit they are near.