First, we need to draw the Lewis structure of C2H4.
In short, these are the steps you need to follow for drawing a Lewis structure:
1. Write the correct skeletal structure for the molecule.
* Hydrogen atoms are always terminal (only one bond)
* Put more electronegative elements in terminal positions
2. Sum the valence electrons from all the atoms.
3. Use a pair of electrons to form a bond between each pair of bound atoms.
4. Add the remaining electrons to satisfy the octet for a more electronegative atom first.
5. If any atoms lack an octet, make a double or triple bond to give them an octet.
The two carbon atoms must be connected because hydrogen cannot have more than one bond and therefore, it cannot be between the two carbon atoms.
There are 2 x 4 + 4 x 1 = 12 electrons and the two of them have been used to make the C-C bond, and eight are used to make the four C-H bonds. So, there are 2 left which we put on the carbon atoms:
Now, what you need to remember is that species with unpaired electrons are called radicals and these are very unstable, and therefore, these electrons are used to make a new bond between the carbon atoms:
There is a double bond between the carbon atoms. One is a sigma and the other is a pi bond.
For the geometries, on each carbon, there are three atoms and no lone pairs which means both electron and molecular geometries are trigonal planar, and the carbon atoms are sp2-hybridized:
Check this 99-question multiple-choice quiz on Geometry and Hybridization:
Geometry and Hybridization Quiz
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