NEET‑Chemistry – Study Notes
Topic: The Periodic Table
Why it matters for NEET
The periodic table is the backbone of chemistry. Questions on trends, block-wise classification, and element properties are standard in NEET. A solid grasp of the table will help you answer multiple‑choice, matching, and short‑answer questions with confidence.
1. Simple Explanation
The periodic table arranges the 94 naturally occurring elements (plus a few synthetic ones) in rows (periods) and columns (groups) according to increasing atomic number (Z). Elements in the same group share the same valence‑electron configuration and therefore display similar chemical behaviour.
- Periods: Horizontal rows (1–7). Each period starts with an alkali metal and ends with a noble gas (except the first period which ends with helium).
- Groups: Vertical columns (1–18). Elements in a group have the same number of valence electrons.
- Blocks: The table is divided into s‑, p‑, d‑, and f‑blocks based on the subshell that is being filled.
2. Key Points
| Feature | Details | Typical Elements | NEET Relevance |
|---|---|---|---|
| Atomic Structure | Elements are defined by their atomic number (Z). | All elements | Important for Noble Gas Nucleation questions |
| Groups (Columns) | 1–18, named (I–VIIIA, VIIIA, VIIIB–XIIIA, XIIB–XIIIB) | 1: Alkali metals; 17: Halogens; 18: Noble gases | Valence‑electron rules for bond formation |
| Periods (Rows) | 1–7 | 1: H, He; 7: Lanthanides/Actinides | Trends: radius, ionisation energy, electronegativity |
| Blocks | s (groups 1,2,18), p (groups 13–18), d (transition metals), f (lanthanides & actinides) | 3d series: Sc–Zn | Transition metal chemistry in NEET questions |
| Metalloids | Sb‑Ar, Te‑Au, etc. | Si, Ge, As, Se | Metalloids’ dual behaviour (covalent & ionic) |
| Noble Gases | +0 oxidation state, low reactivity | He, Ne, Ar, Kr, Xe, Rn | Inert gas behaviour, He‑based medical imaging |
| Alkali & Alkaline Earth | Highly reactive, form +1 & +2 ions | Li, Na, K, Mg, Ca | Relevance in physiological ion transport |
| Trend 1 – Atomic Radius | Increases down a group, decreases across a period | 1 Å → 0.5 Å across period | Important for bond length predictions |
| Trend 2 – Ionization Energy (IE) | Increases across a period, decreases down a group | 13 eV → 1 eV across period | Ionisation energy correlates with reactivity |
| Trend 3 – Electronegativity (Pauling) | Increases across a period, decreases down a group | 4.0 → 0.7 across period | Determines bond polarity |
| Trend 4 – Electron Affinity | Becomes more negative across a period | –0.4 eV → –2.8 eV across period | NEET often asks “most exothermic” |
| Ionisation Energy of Helium | Highest of all elements (24.6 eV) | Example of a “universal constant” | |
| Lanthanides & Actinides | f‑block, 14 elements each | La–Lu, Ac–Lr | Radioactive isotopes in medical diagnostics |
| IUPAC Rules for Naming | Nomenclature of organometallics, coordination complexes | Coordination numbers, oxidation states | For advanced NEET questions |
3. Worked Example
Question (Typical NEET style)
“Which of the following elements would most likely form a covalent bond with hydrogen in an aqueous solution?
A. Lithium (Li)
B. Oxygen (O)
C. Chlorine (Cl)
D. Sodium (Na)”
Step‑by‑step Solution
-
Identify Valence Electrons
- Li: 1 valence e⁻
- O: 6 valence e⁻
- Cl: 7 valence e⁻
- Na: 1 valence e⁻
-
Determine Electronegativity (EN) (Pauling scale)
- Li = 1.0, Na = 0.9, O = 3.5, Cl = 3.0
-
Rule of Thumb
- Covalent bonding favours elements with EN ≥ 2.0 (moderate to high).
- Ionic bonding favours elements with EN ≤ 1.5.
-
Apply to Options
- Li and Na: EN ≈ 1 → Ionic.
- O and Cl: EN > 2 → Covalent.
-
Select the Most Covalent
- Both O and Cl can form covalent bonds, but O is more electronegative and typically forms covalent bonds with hydrogen in water (e.g., H₂O).
- Answer: B. Oxygen.
Key Takeaway – Use EN and valence electrons to predict bonding type. This is a common NEET reasoning pattern.
4. Quick Revision Summary (Bullet‑Point)
- Layout: Periods 1–7, Groups 1–18, Blocks (s, p, d, f).
- Groups:
- 1 (IA) – Alkali metals (highly reactive, +1).
- 2 (IIA) – Alkaline earth metals (reactive, +2).
- 13–18 – p‑block (metals, metalloids, halogens, noble gases).
- 3–12 – d