Chem Tool #1 · DE Bio 101 Unit 2 · Campbell Ch. 2 and 3
An atom’s outer shell wants eight electrons, and hydrogen wants two. However many it is short by is how many bonds it makes, and that number never changes: carbon four, nitrogen three, oxygen two, hydrogen one. Build seven molecules by spending each atom’s budget down to zero.
Tap one atom, then another, to bond them. Tap a bond again to make it a double. Tap a finished bond to remove it. The number on each atom is how many bonds it still owes.
When all seven are built, look back at the last three. Each one hangs a small group off a carbon skeleton, and each of those groups is what gives a macromolecule its behaviour in water. That is where Unit 3 begins.
On paper, draw a chain of five carbons joined to each other. Give every carbon its full four bonds using hydrogens, then replace one end hydrogen with an —OH. Mark which end of that molecule water will stick to. Do it without looking anything up. If you stall, the atom you stalled on is the one to go back to.