Mnemonic 1: VSEPR Shape from Steric Number

"2 Straight, 3 Plane, 4 Tet, 5 Bi, 6 Oct"

• SN=2 → Straight (linear, 180°)
• SN=3 → Plane (trigonal planar, 120°)
• SN=4 → Tetrahedral (109.5°)
• SN=5 → Bipyramidal (trigonal, 90°/120°)
• SN=6 → Octahedral (90°)

Mnemonic 2: MO Mixing Rule

"BONCe mixed, Oxygen forward"

• B_{2}, O (not exactly, but for Z≤7: B, C, N) → mixed order (π2p before σ2p)
• O{2}, F{2} (Z > 7) → forward/normal order (σ2p before π2p) Better: "Before Oxygen: π before σ. Oxygen onwards: σ before π"

Mnemonic 3: Fajan's Rules

"Small Cat, Big Annie, High Charge = Covalent"

• Small cation = small cation → high charge density → more polarising
• Big Anion = large anion → more polarisable electron cloud
• High charge = higher oxidation state → more polarising

Mnemonic 4: Lone Pair Placement in TBP (SN=5)

"Lone pairs Love Equatorial"

• In TBP geometry (SN=5), lone pairs ALWAYS go to equatorial positions
• Equatorial = 120° to 2 neighbours + 90° to 2 neighbours → LESS repulsion than axial (90° to 3 neighbours)

Mnemonic 5: Bond Order = Bond Strength = 1/Bond Length

"Order Up = Stronger Up = Length Down"

• Higher bond order → stronger bond → shorter bond
• BO 1 < 2 < 3 matches: C–C > C=C > C≡C for length (decreasing)
• BO 1 < 2 < 3 matches: C–C < C=C < C≡C for energy (increasing)

Mnemonic 6: μ = 0 Molecules (Symmetric)

"Linear, Planar, Tetra — Symmetric = Zero (μ)"

• Linear: $BeCl_{2}$, $CO_{2}$, $CS_{2}$ (no lone pairs on central atom)
• Planar: $BF_{3}$, $BCl_{3}$, $SO_{3}$ ($sp^{2}$, no lone pairs)
• Tetrahedral: $CH_{4}$, $CCl_{4}$, $SiF_{4}$ (4 identical bonds)

Mnemonic 7: Paramagnetic Species (unpaired electrons)

"$O_{2}$ $B_{2}$ NO $O_{2}^{+}$ $O_{2}^{-}$ — These are Paramagnetic Friends"

• $O_{2}$: 2 unpaired in π*2p
• $B_{2}$: 2 unpaired in degenerate π2p (Z ≤ 7)
• NO: 1 unpaired in π*
• $O_{2}^{+}$: 1 unpaired
• $O_{2}^{-}$: 1 unpaired