GPAT Chemistry – Study Notes on The Periodic Table
Audience: First‑year pharmacy students preparing for the GPAT exam.
Format: Markdown – concise, visually organised, and easy to skim.
Sections:
- Simple Explanation
- Key Points (trends, classification, special groups)
- Worked Example
- Quick Revision Summary
1. Simple Explanation
The periodic table arranges all known elements by atomic number (protons) and groups them so that elements with similar valence electron configurations and therefore similar chemical properties appear in the same column (group). The horizontal rows are called periods and represent the filling of successive electron shells.
Why it matters for GPAT
– Recognise element behaviour in drug‑design (e.g., halogen substitution).
– Predict physical properties (melting point, reactivity).
– Understand trends that influence pharmacokinetics (solubility, lipophilicity).
2. Key Points
| Category | Details | Why it’s important for GPAT |
|---|---|---|
| Classification | Groups (1–18), Periods (1–7), Blocks (s, p, d, f) | Helps locate an element quickly and know its general behaviour. |
| Periodic Trends | <ul><li>Atomic radius ↓ across a period, ↑ down a group</li> <li>Ionization energy ↑ across a period, ↓ down a group</li> <li>Electron affinity ↑ (more negative) across a period, ↓ down a group</li> <li>Electronegativity ↑ across a period, ↓ down a group</li> <li>Metallicity ↓ across a period, ↑ down a group</li></ul> | Predict reactivity, bonding types, and drug molecule properties. |
| Effective Nuclear Charge (Z<sub>eff</sub>) | ( Z_{\text{eff}} = Z - S ) (S = shielding electrons) | Explains why ionization energy and electronegativity rise across a period. |
| Valence Electrons | Count of electrons in the outermost shell | Determines typical oxidation state and type of bonding. |
| Special Groups | <ul><li>Alkali metals (Group 1) – highly reactive, form +1 ions.</li> <li>Alkaline earth metals (Group 2) – +2 ions.</li> <li>Halogens (Group 17) – form −1 ions, very high electronegativity.</li> <li>Noble gases (Group 18) – inert, full valence shells.</li> <li>Transition metals (Groups 3–12) – variable oxidation states, d‑orbital participation.</li> <li>Lanthanoids & Actinoids – f‑block, complex chemistry, radioactive.</li></ul> | Common in drug molecules (e.g., Na⁺ in electrolytes, Cl⁻ in salts, Fe in haem). |
| Periodic Blocks | s‑block (Groups 1–2), p‑block (Groups 13–18), d‑block (transition metals), f‑block (lanthanides/actinides) | Determines electron configuration and reactivity patterns. |
| Metalloid Region (Staircase) | Elements between metals and non‑metals (e.g., B, Si, Ge, As, Se, Te, Po) | Often exhibit dual behaviour; important in semiconductor drugs. |
| Ionic vs. Covalent Character | Determined by electronegativity difference (Δχ); Δχ > 1.7 → ionic, < 1.7 → covalent | Influences drug solubility and binding. |
Quick Trend Chart
| Period 3 (Na to Ar) | Na (3s¹) → Mg (3s²) → Al (3p¹) → Si (3p²) → P (3p³) → S (3p⁴) → Cl (3p⁵) → Ar (3p⁶) |
|---|---|
| Radius | ↓ (Na > Mg > Al > … > Ar) |
| Ionization Energy | ↑ (Na < Mg < Al < … < Ar) |
| Electronegativity | ↑ (Na < Mg < … < Ar) |
| Electron Affinity | ↓ (least negative for Na, most negative for Ar) |
3. Worked Example
Problem:
Predict the order of atomic radii for the following elements: Li, Be, B, C (all in Period 2). Explain the trend using electronic configuration and effective nuclear charge.
Step‑by‑Step
- Write the electron configurations (outermost shell = 2s/2p).
| Element | Configuration | Valence electrons |
|---|---|---|
| Li | 1s² 2s¹ | 1 |
| Be | 1s² 2s² | 2 |
| B | 1s² 2s² 2p¹ | 3 |
| C | 1s² 2s² 2p² | 4 |
- Identify the nuclear charge (Z).
| Element | Z |
|---|---|
| Li | 3 |
| Be | 4 |
| B | 5 |
| C |