What makes an oil an oil? How is it different from any number of water suspensions? What do olive oil and, say, motor oil have in common that makes them both oils?
In: Chemistry
>What is an oil
An oil is any nonpolar chemical substance that is a viscous liquid at ambient temperatures and is both hydrophobic (does not mix with water, literally “water fearing”) and lipophilic (mixes with other oils, literally “fat loving”).
>what makes it so different from water-based liquids?
A water molecule consists of 2 hydrogen atoms and an oxygen atom.
The oxygen atom has 6 electrons in its outer shell, 4 of which will form 2 pairs of 2 while the others each get “shared” with a hydrogen atom, and these 4 sets of electromagnetic charge will naturally try to spread as far apart as possible, which in 3 dimensional space puts them at 104.4° angles.
This is important, because it puts the positively charged hydrogen atoms on one side of the oxygen atom, while on the other side you get all negatively charged electrons. This makes the molecule as a whole polar, like a tiny magnet except it’s an electric rather than a magnetic magnet, which lets it stick more strongly to other polar molecules.
Oils meanwhile – as a consequence of how they’re defined as hydrophobic and lipophilic – *don’t* have this sort of an electron/proton charge asymmetry, so their molecules are all non-polar. Non-polar molecules generally aren’t as sticky as polar ones of the same size, which is why methane and ozone are both gasses, but when they get big enough to stick together into a liquid at room temperature they stick to other non-polar molecules more strongly.
As a bit of bonus info, there are also molecules that are polar at one end but neutral at the other end. This is hugely useful for things like making cell membranes (where the non-polar ends all point together in the middle of the membrane, letting their polar ends point both in and out to meet the watery interior and surroundings of a cell), soaps, and organic solvents like ethanol.
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