Study TipsMay 18, 20268 min read
MDCAT Atomic Structure & Periodic Table 2026 — Trends, Quantum Numbers, Configurations
Premeth Team
Meth Experts
Atomic Structure (~3 MCQs) and the Periodic Table (~2–3 MCQs) together cover ~12% of the MDCAT Chemistry section. They are foundational chapters — weak here cascades into every other topic. Master quantum numbers and periodic trends first.
- Atomic Structure MCQs — 3 of 45 Chemistry MCQs
- Periodic Table MCQs — 2–3 of 45
- Quantum numbers — n, l, ml, ms
- Subshell order — 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f...
Source: PMDC MDCAT 2026 syllabus; UHS Chemistry pattern analysis 2008–2024.
Quantum Numbers (Memorise Cold)
- Principal (n) — energy level. Values 1, 2, 3, ... Determines shell size.
- Azimuthal (l) — subshell shape. Values 0 to (n−1). s=0, p=1, d=2, f=3.
- Magnetic (ml) — orbital orientation. Values −l to +l. p has 3 orbitals (−1, 0, +1).
- Spin (ms) — electron spin. Values +½ or −½.
Electron Configuration Rules
- Aufbau principle — fill lowest-energy orbitals first.
- Pauli exclusion — max 2 electrons per orbital, opposite spins.
- Hund's rule — fill all orbitals in a subshell singly before pairing.
- Anomalies — Cu (3d104s1) and Cr (3d54s1) — classic trap MCQs.
Periodic Trends
| Property | Across a period (L → R) | Down a group |
|---|---|---|
| Atomic radius | Decreases | Increases |
| Ionic radius (cation) | Decreases | Increases |
| Ionisation energy | Increases | Decreases |
| Electron affinity | Increases (mostly) | Decreases |
| Electronegativity | Increases | Decreases |
| Metallic character | Decreases | Increases |
Trap MCQs
- “Element with highest electronegativity?” — Fluorine (4.0 on Pauling scale).
- “First ionisation energy is greater for B or Be?” — Be is greater (full 2s subshell — B has the higher-energy 2p electron easier to remove).
- “Why does Cu have 3d104s1?” — full-d-orbital extra stability.
- “Highest atomic radius in Period 3?” — Sodium (leftmost).
- “Which is more electronegative: Cl or F?” — F (always trumps Cl).
FAQ
Q: How many electrons in d-subshell?
Maximum 10 (5 orbitals × 2 spins).
Q: Why is the 4s filled before 3d?
4s is lower in energy than 3d before they overlap (Aufbau in real atoms).
Q: Are the f-block elements tested?
Rarely — PMDC syllabus focuses on s, p, d blocks. F-block knowledge is bonus.
These two chapters are the foundation of every other Chemistry topic. Drill Atomic Structure and Chemistry hub together.
Related Tags
#MDCAT#Chemistry#Atomic Structure#Periodic Table
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