Imagine molecules and atoms as a bunch of drunks in a room. If they don’t bump into each other, no reaction will happen. There’s more than an Avogadro’s number of molecules used in any lab-intended reaction to make sure the molecules bump into each other.
Proteins react whenever they bump into another molecule that fits their active site. Molecules fitting into an active site is like fitting Legos, puzzle pieces, or locks and keys. If the pieces don’t fit, there will be no reaction. The lock and key analogy often is favored because the protein typically changes shape after another molecule fits into its active site. Not all reactive sites are identified and understood.
Whenever you see a double-bonded atom (often oxygen) and the same atom negatively charged with a single bond, and both atoms bonded to the same central atom, imagine they’re spinning, the double-bond and the single-bond are switching many times per second. This goes to the stability of the molecular species, like peddling a bike stabilizes it or like a gyroscope.
Aldehydes aren’t going to give up their double-bonded oxygen or single-bonded hydrogen.
Fluorine is a “skinny slut”. It tends to take electrons whenever it can. It’s one of the smallest atoms and is the most electronegative.
Some weird triangular molecules occur when boron is involved.
Predictions for reactions based on the Periodic Table fall apart after Row 3, and get worse as you go down the Table.
Noble gasses don’t react because they have a full octet of electrons in their outer shell. It’s been traditionally considered “noble” amongst human beings not to react.
After taking microbiology, you’ll understand the “smell test”. If it doesn’t stink, it’s probably okay to eat.
The molecular properties of water are a miracle. When in doubt, explain anything and everything by citing hydrogen bonding in water.