Ten core categories and ten nuance cases, built step by step: first the Lewis structure, then its 3D shape.
Fig 1Lewis bench← → step · ↑ ↓ category · click the knob or slideCH₄ · step 1 of 6
Step 1 of 6
Beads placed in this step: one bead is one valence electronAtom pucks and bond bars, two beads to a barDial: beads still in the tray, a major tick every 8Every Lewis structure is built the same six ways round. Pour the valence electrons into the tray, set the atoms on the dish, spend two beads on each bond, fill the outer atoms to eight, park what is left on the central atom, then turn lone pairs into double or triple bonds until the octets and formal charges come out right. No bead is ever made or lost.
Single bonds only
CH₄methane
4 (C) + 4×1 (H) = 8 valence electrons.
C goes in the middle. H can only make one bond, so it is always an outer atom.
4 single bonds × 2 = 8 electrons. 0 left.
The outer atoms are all H, which is full with 2. Nothing to add; 0 left.
No electrons are left over, so the central atom gets nothing here.
C has 8 electrons, all in bonds; each H has its 2. Every formal charge is 0, so this is the structure.
Ten core categories
Nuance Ten more, each with a twist
The same molecules as the VSEPR nuance set: expanded octets with lone pairs, a noble gas that bonds, a radical with formal charges, and a double bond that has to go to O.
Fig 2VSEPR stand← → step · ↑ ↓ molecule · drag to turnCH₄ · Lewis layout
Step 1 of 6
Atoms and bonds: a double or triple bond is still one domainLobes: lone pairs (two dots) and lone electrons (one dot)Angle arc and gauge: the bond angle, measured from the modelVSEPR in six moves. Read the domains off the Lewis structure, count them (a multiple bond is one), let them spread as far apart as they can, put lone pairs where they collide least, name the shape from the atoms alone, then let lone pairs and fat double bonds bend the angles to their measured values. The lamps count domains: bonds lit, lone pairs grey.
1 · Single bonds only
CH₄methane
AX₄ · tetrahedral
Lewis structure of CH₄: C has 4 bonded atoms.
4 electron domains on C.
4 domains spread as far apart as possible: tetrahedral, 109.5°.
No lone pairs to place: every domain is a bond.
Name only the atoms, not the lone pairs: AX₄ → tetrahedral.
H–C–H 109.5°. With no lone pairs, every angle stays at the ideal 109.5°. Nonpolar: four identical bonds cancel.
The same ten categories
Nuance Ten more, each with a twist
The same ten as the Lewis nuance set. Shapes the first ten never reach: lone pairs that have to choose a position, the octahedral family, and angles that move away from the textbook value.