Atomic Structure Cheatsheet
Cheat Codes & Shortcuts
- Atom: Smallest unit of matter, composed of protons, neutrons, electrons.
- Atomic Number (Z): Number of protons in the nucleus.
- Mass Number (A): Total number of protons and neutrons.
- Isotopes: Atoms with same Z, different A.
- Electron Configuration: Distribution of electrons in shells & subshells.
- Aufbau Principle: Electrons fill lowest energy orbital first.
- Pauli Exclusion Principle: No two electrons have same set of quantum numbers.
- Hund's Rule: Orbitals in same subshell get one electron each before pairing.
- Bohr's Model: Electrons revolve in discrete orbits with quantized energy.
- Quantum Numbers: n, l, m, s — describe properties/position of electrons.
Quick Reference Table
| Term | Definition / Formula | Example / Note |
|---|---|---|
| Atomic Number (Z) | Number of protons | Carbon: Z = 6 |
| Mass Number (A) | Protons + Neutrons | C-12: 6p + 6n = 12 |
| Isotope | Same Z, diff. A | C-12 & C-14 |
| Electron Configuration | Arrangement of electrons | C: 1s22s22p2 |
| Bohr's Radius | \( r_n = n^2 a_0 \) | First orbit: n=1, r1=0.529Å |
| Quantum Numbers | n, l, m, s | n=principal, l=azimuthal, m=magnetic, s=spin |
Advice
Step 1: Determine atomic number & mass number from periodic table.
Step 2: Write electron configuration using Aufbau order.
Step 3: Apply Pauli & Hund rules for electrons in orbitals.
Step 4: Use quantum numbers for detailed electron position.
Step 5: Isotope problems: Same Z, use A to find neutrons.
Atomic Structure Quick Tips
- Atomic number (Z): Always equals number of protons and electrons (neutral atom).
- Mass number (A): A = Z + neutrons.
- Aufbau order: Fill orbitals: 1s → 2s → 2p → 3s → 3p → 4s → 3d...
- Pauli exclusion: Max 2 electrons per orbital, opposite spins.
- Quantum numbers: For the nth shell, max electrons = 2n2.
Atomic Structure Speed Quiz
Test your speed with 5 atomic structure questions! You have 30 seconds per question.
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