Gym · Bonding & structure

Lewis structures: the electron ledger

A Lewis structure is an electron ledger: count the valence electrons, spread them into bonds and lone pairs, and the shape follows. These drills give you a molecule and ask for its valence-electron total, the number of electron domains around the central atom, or its molecular shape. Type the counts (they are exact — this is integer accounting, machine-checked); if you slip, the drill names the mistake — counting every electron instead of just the valence ones, forgetting a lone pair is a domain, or calling a double bond two domains. The shape questions offer the electron-domain geometry as a tempting wrong answer: lone pairs are invisible in the named shape.