A working folder for teachers, students, parents, and anyone putting evidence to use.
A carbon skeleton holds a molecule together. The functional groups hanging off it are the parts that react, and each one has a shape it actually takes in space. Pick a group, then drag the model to turn it.
Atoms nearer to you are drawn larger and brighter. Two dots beside an atom are a lone pair — electrons it keeps rather than shares. Lone pairs take up room and push the bonds, which is why the oxygen in a hydroxyl is bent and the carbon in a methyl is not.
Three ways through: name it from the structure, draw it from the name, or say what it does. Answer out loud or on paper before you turn the card over.
Two of these carry a charge inside a cell, and one carries two. A carboxyl gives up its hydrogen and goes negative; an amino picks one up and goes positive; a phosphate sits at minus two. That is why an amino acid has a positive end and a negative end at the same time, and why the backbone of DNA repels itself down its whole length.
On paper. Draw a four-carbon chain. Put a carboxyl on one end and an amino on the other, then mark the charge each one carries at cell pH. Now put a methyl group in the middle and mark which part of the molecule water will avoid. Do it without looking anything up. Whichever group you stall on is the one to come back to.
Bond angles here are built from internal coordinates and measured back out, against values for methanol, acetic acid, methylamine, methanethiol and phosphate esters. Lone pairs are placed by construction, in the plane that bisects the bonds, rather than drawn where they look right.