Study guide · Make-up prep
Chemistry Honors · exam skills
Ch 4 skills that still need reps, plus Ch 6 bonding for the exam on Thu Nov 19 (Pacific time).
Ch 6 recap matches the printable memory sheet (gold button). Ch 4 notes below are standard exam skills from the posted exam description — not a claim about any one missed item (Schoology doesn’t show question-level scores).
💡 Ch 4 · light calculations
- Speed of light: c = λν (wavelength × frequency). So λ = c/ν and ν = c/λ.
- Energy of a photon: E = hν or E = hc/λ. Higher frequency (or shorter wavelength) means more energy.
- c and h are constants. Watch units: wavelength often in nm (1 nm = 10⁻⁹ m).
If ν goes up and c stays the same, λ goes down.
🔢 Ch 4 · quantum numbers
| Symbol | Name | What it tells you |
|---|
| n | Principal | Shell / energy level (1, 2, 3, …) |
| ℓ | Angular momentum | Subshell shape: 0 = s, 1 = p, 2 = d, 3 = f |
| mℓ | Magnetic | Which orbital in that subshell (from −ℓ to +ℓ) |
| ms | Spin | +½ or −½ |
🧲 Ch 4–5 · electron configurations
- Fill low energy first (Aufbau): 1s 2s 2p 3s 3p 4s 3d …
- Pauli: an orbital holds at most 2 electrons, opposite spins.
- Hund: spread electrons out in a subshell before pairing them.
- Noble-gas shortcut: Na (11) is 1s² 2s² 2p⁶ 3s¹ or [Ne] 3s¹.
The Ch 5 quiz also asked for group/period names and noble-gas configurations. Ch 6 (below) is the Nov 19 exam.
🎯 Ch 6 · Valence electrons
| Group | 1 | 2 | 13 | 14 | 15 | 16 | 17 | 18 |
|---|
| Valence e⁻ | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 (He = 2) |
Ions: add 1 e⁻ for each negative charge, subtract 1 e⁻ for each positive charge. NH₄⁺ = 8 · CO₃²⁻ = 24.
🧪 Lewis structures (7 moves)
- Count total valence e⁻ (adjust for charge).
- Central atom: least electronegative (usually C; never H).
- Connect with single bonds (each bond = 2 e⁻).
- Fill outer atoms to an octet (H only gets 2).
- Leftover e⁻ go on the central atom as lone pairs.
- Central atom short of an octet? Make a double/triple bond.
- Check: electrons drawn = electrons counted. Formal charge = V − (lone-pair e⁻) − ½(bonding e⁻).
Draw every lone pair. Write the shape name next to every structure.
Octet exceptions: H = 2 · Be = 4 · B = 6 (BF₃) · Period 3+ can expand (PCl₅ = 10, SF₆ = 12).
↔️ Resonance
Used when more than one valid Lewis structure exists. Only electrons move — atoms stay put. The real molecule is an average (hybrid). Classics: O₃, NO₃⁻, CO₃²⁻.
📐 VSEPR shapes (AXE)
A = central atom · X = atoms bonded · E = lone pairs on the center. A double or triple bond is ONE domain.
| AXE | Shape | Angle | Example |
|---|
| AX₂ | Linear | 180° | CO₂ |
| AX₃ | Trigonal planar | 120° | BF₃ |
| AX₂E | Bent | <120° | SO₂ |
| AX₄ | Tetrahedral | 109.5° | CH₄ |
| AX₃E | Trigonal pyramidal | ~107° | NH₃ |
| AX₂E₂ | Bent | ~104.5° | H₂O |
| AX₅ | Trigonal bipyramidal | 90° & 120° | PCl₅ |
| AX₆ | Octahedral | 90° | SF₆ |
Lone pairs push harder than bonding pairs, so angles shrink: 109.5° → 107° → 104.5°.
⚡ Polarity & IMFs
- Polar bonds + unsymmetrical shape (H₂O, NH₃) = polar molecule.
- Symmetrical shapes cancel (CO₂, BF₃, CH₄) = nonpolar.
- Hydrogen bonding: H bonded directly to F, O, or N — strongest IMF, which is why water boils so high.
Electronegativity cutoffs vary by textbook (common sets include 0.3/1.7, 0.4/1.7, 0.4/1.8, and 0.5/2.0). Use the numbers from your teacher’s Ch 6 notes, not a guessed cutoff, when you classify nonpolar, polar covalent, or ionic bonds.