Explain what fatty-acid notation such as 18:3 means, and distinguish saturated, monounsaturated, and polyunsaturated fatty acids.

### What a good answer covers - The first number records the fatty acid’s carbon count. - The second number records the number of carbon-carbon double bonds. - Saturated fatty acids have zero double bonds. - Monounsaturated fatty acids have one, while polyunsaturated fatty acids have multiple. ### The concept Double bonds affect fatty-acid shape and packing. Saturated chains can pack relatively closely, while double bonds, especially cis double bonds, introduce bends that disrupt packing. Notation such as 18:3 does not alone give double-bond positions or geometry, so additional notation is needed for those details. ### Terms - **Saturated**: containing no carbon-carbon double bonds in the fatty-acid chain. - **Monounsaturated**: containing one carbon-carbon double bond. - **Polyunsaturated**: containing two or more carbon-carbon double bonds.