type: mnemonic_note | subtopic: Memory Techniques

Mnemonic 1: Spectral Series → Region

"Little Boys Play" → Lyman, Balmer, Paschen → UV, Visible, IR

• L = Lyman = UV (Level 1)
• B = Balmer = Visible (Balmer has two L's — it Lies in Light/Visible)
• P = Paschen = IR (Pretty Infrared) Extended: Brackett = far IR (Back far), Pfund = far IR (Pfar)

Mnemonic 2: KE and PE in Bohr Model

"KOE-PDE" — "KE Opposes E; PE Doubles E"

• KE = −E (opposite sign to total energy)
• PE = 2E (double the total energy, same sign)
• Quick check: KE + PE = −E + 2E = E ✓

Mnemonic 3: Spectral Lines Count

"Half of n times (n minus one)"

• N = n(n−1)/2
• n=4: half of 4×3 = half of 12 = 6. Done.
• NOT $n^{2}$ (16), NOT 2n (8). It's n(n−1)/2.

Mnemonic 4: Alpha and Beta Decay Rules

"Alpha subtracts a He-4 block: −4 and −2" "Beta-minus: minus flips: n→p raises Z by 1"

• Alpha: A−4, Z−2 (He-4 = 2 protons, 2 neutrons)
• β^{-}: A=same, Z+1 (neutron becomes proton)
• β^{+}: A=same, Z−1 (proton becomes neutron)
• γ: Nothing changes (just energy emitted)

Mnemonic 5: Half-life vs Mean Life

"Mean > Half, by 44%"

• τ = 1.443 × t_{1}/_{2} (always GREATER)
• At t = τ: N = $N_{0}$/e = 36.8% (memorize: e ≈ 2.718, 1/e ≈ 0.368)
• At t = t_{1}/_{2}: N = $N_{0}$/2 = 50%

Mnemonic 6: Nuclear Radius

"R = R-nought times cube-root of A"

• $R_{0}$ = 1.2 fm (remember: "One-point-two fermi")
• R(Al-27) = 1.2 × ∛27 = 1.2 × 3 = 3.6 fm (easy: 27 = 3^{3})
• R(U-238) = 1.2 × ∛238 ≈ 1.2 × 6.2 ≈ 7.4 fm

Mnemonic 7: Bohr Radius Proportionality

"n-squared over Z" → "NSQZ"

• r_n = 0.529 × $n^{2}$/Z Å
• Bigger orbit → larger n ($n^{2}$), larger Z → smaller orbit (more attraction)