Saturated and unsaturated fatty acids
Extra knowledge — classifying fatty acids
The fatty acids used to build a lipid fall into two kinds. One question decides which: can any more hydrogen be attached to the carbon atoms?
Saturated fatty acids
Hydrogen: the maximum number of hydrogen atoms that can bond to each carbon atom is present
At room temperature: solid or semi-solid
Everyday name: usually "fat"
Unsaturated fatty acids
Hydrogen: that maximum is not present — more hydrogen could still be added
At room temperature: liquid
Everyday name: usually "oil"
What "saturated" means
Saturated means filled up. The carbon chain of a saturated fatty acid is completely filled with hydrogen, so not one more atom will fit.
Why are fats solid and oils liquid at room temperature?
This answers why fats are solid and oils are liquid at room temperature. It depends on whether the fatty acids in them are saturated or unsaturated.