What do lines between elements represent in a compound?

The lines between the atoms of the elements in a compound represent covalent bonds. One line equals one pair of shared electrons. The lines are used to represent the structure of the molecule, how the atoms bond with one another, rather than just the number of each element in a molecule. One line represents one pair of electrons, or a single bond. Two lines represent two pairs of electrons, or a double bond, and three lines represent a triple bond.