How can I draw a possible structure of C2H4?

Here's one way to figure out the structure:

1. Write all possible connections for the carbon atoms.

C-C

2. Add the H atoms.

Put two H atoms on each C.

3. Count the number of , ##V##, you actually have available.

##V## =2C + 4H = 2×4 + 4×1 = 12.

4. Calculate ##P##, the number of π electrons there must be in the molecule:

##P = 6n + 2 – V##

where ##n## is the number of non-hydrogen atoms in the molecule.

##P## = 6×2 + 2 - 12 = 2 π electrons. So there is one double bond in the molecule.

5. Draw the new structure.

This time insert the double bond.

And you have the structure.

Here's another way to develop the structure.