What a learner can do afterwards
- Starts every arrow at an electron source, a lone pair or a bond, and ends it where the pair arrives
- Assigns formal charges before and after a step and checks that charge balances
- Uses a single-headed arrow for radical steps and a double-headed arrow for pairs, without mixing them
- Spots and corrects an arrow that would give an atom more bonds than it can have
1 · Read
A curly arrow is a claim about where electrons move, not decoration. Its tail sits exactly on the electron source: a lone pair or a bond. Its head lands exactly where the pair arrives: a new bond or a new lone pair. Read every arrow as one sentence with a subject and a destination, and vague arrows will embarrass you fast.
Check every step with formal charges, the bookkeeping number found by taking valence electrons and subtracting assigned ones. Add the charges before the step and after it. The two totals must match, since electrons only move and never appear or vanish. A mismatch convicts one of your arrows.
Mind the two head shapes and the bonding cap. A double headed arrow moves a whole pair, while a single headed fishhook moves one electron in a radical step, and mixing them up changes the story. No arrow may hand an atom more bonds than it can hold: carbon stops at four. An arrow that would build a five bond carbon is illegal, so redraw it to a legal destination.
Arrows move electrons only, never atoms, which is also why resonance arrows only shuffle pairs between fixed atoms. Give each elementary step its own arrow set and check tails, heads, charges, and octets in that order. Fluency in this grammar is fluency in mechanism.
Tails at electron sources, heads at destinations, charges balanced, octets respected.
2 · Watch
Take it off screen
Where it sits
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.