The Lewis structure of a compound can be generated by trial and error. c2h2 would turn into what is known as Ethyne. Two Hydrogens are on the top and lower parts and sandwiched in btwn these two is the chained portion of carbon-carbon and the 3rd and 4th hydrogen atom. Again the sequence for the carbon is a long drawn line chaining them together and remember on both sides on the left side top and lower branches is the second sets of Hydrogen.
H: _____ :H
C C
_____
H: :H
Remember that Hydrogen (H) atoms always go on the outside of a Lewis Structure.
