Try it on paper first. A hint, the key idea and the worked solution are here when you need them.
Ethanal, , has a double bond between its second carbon atom and the oxygen atom. How many pairs of electrons are shared in one molecule? Which bond holds two of them? Use the valencies C , O and H .
A covalent bond is a pair of electrons shared by two atoms. One pair is a single bond, two pairs a double bond, three pairs a triple bond. Valency: H , O , N , C , Cl . Number of bonds, counting a double bond as two, = (sum of the valencies) .
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Valencies. .
Step 2. Shared pairs. pairs.
Step 3. Sort them. One carbon to carbon bond, four carbon to hydrogen bonds, and the C=O double bond, which counts two: .
Answer: shared pairs. The C=O double bond holds two of them.
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