In unsaturated fats, what is missing in the fatty acid chain?
Hydrogen atoms are missing.
In unsaturated fats, the fatty acid chain is missing hydrogen atoms. This is because unsaturated fatty acids have at least two double-bonded carbon atoms, so they cannot bond with the maximum number of hydrogen atoms.
Both fatty acids in the diagram below have 7 carbon atoms. The saturated fatty acid has no double bonded carbon atoms, so it has the maximum number hydrogen atoms possible (13) which is what is meant by saturated. The unsaturated fatty acid has a double bond between two carbon atoms. So there are two fewer hydrogen atoms (11), and it is not saturated. Since it has only one double bond between two carbon atoms, it is monounsaturated.