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Classification of Elements
Advanced Periodic Trends & Practice for JEE/NEET
3.7.1 Detailed Periodic Trends in Physical Properties
This section provides a deeper dive into the periodic variations of key physical properties, including illustrative data tables and conceptual visualizations to help you grasp the trends more effectively.
(a) Atomic Radius (Detailed Data & Trends)
Atomic radius provides insight into the size of an atom. Its trends are fundamental to understanding many other periodic properties.
Atomic Radii/pm Across Periods (Table 3.6a)
| Atom (Period II) | Li | Be | B | C | N | O | F |
|---|---|---|---|---|---|---|---|
| Atomic Radius | 152 | 111 | 88 | 77 | 74 | 66 | 64 |
| Atom (Period III) | Na | Mg | Al | Si | P | S | Cl |
|---|---|---|---|---|---|---|---|
| Atomic Radius | 186 | 160 | 143 | 117 | 110 | 104 | 99 |
Conceptual illustration of atomic radius decreasing across a period (e.g., Period 2).
Atomic Radii/pm Down a Family (Table 3.6b)
| Atom (Group I) | Atomic Radius | Atom (Group 17) | Atomic Radius |
|---|---|---|---|
| Li | 152 | F | 64 |
| Na | 186 | Cl | 99 |
| K | 231 | Br | 114 |
| Rb | 244 | I | 133 |
| Cs | 262 | At | 140 |
Conceptual illustration of atomic radius increasing down a group (e.g., Group 1).
(c) Ionization Enthalpy (Detailed Trends)
Ionization enthalpy is a critical property influencing metallic character and reactivity.
Conceptual illustration of ionization enthalpy trends across a period (e.g., Period 2, showing anomalies).
Conceptual illustration of ionization enthalpy decreasing down a group (e.g., Group 1).
(d) Electron Gain Enthalpy (Detailed Data & Trends)
Electron gain enthalpy reflects an atom’s tendency to accept an electron.
Electron Gain Enthalpies / (kJ mol⁻¹) (Table 3.7)
| Group 1 | $\Delta_{eg}H$ | Group 16 | $\Delta_{eg}H$ | Group 17 | $\Delta_{eg}H$ | Group 0 | $\Delta_{eg}H$ |
|---|---|---|---|---|---|---|---|
| H | -73 | He | +48 | ||||
| Li | -60 | O | -141 | F | -328 | Ne | +116 |
| Na | -53 | S | -200 | Cl | -349 | Ar | +96 |
| K | -48 | Se | -195 | Br | -325 | Kr | +96 |
| Rb | -47 | Te | -190 | I | -295 | Xe | +77 |
| Cs | -46 | Po | -174 | At | -270 | Rn | +68 |
(e) Electronegativity (Detailed Data & Trends)
Electronegativity is crucial for predicting bond character and chemical reactivity.
Electronegativity Values (Pauling scale) Across Periods (Table 3.8a)
| Atom (Period II) | Li | Be | B | C | N | O | F |
|---|---|---|---|---|---|---|---|
| Electronegativity | 1.0 | 1.5 | 2.0 | 2.5 | 3.0 | 3.5 | 4.0 |
| Atom (Period III) | Na | Mg | Al | Si | P | S | Cl |
|---|---|---|---|---|---|---|---|
| Electronegativity | 0.9 | 1.2 | 1.5 | 1.8 | 2.1 | 2.5 | 3.0 |
Electronegativity Values (Pauling scale) Down a Family (Table 3.8b)
| Atom (Group I) | EN Value | Atom (Group 17) | EN Value |
|---|---|---|---|
| Li | 1.0 | F | 4.0 |
| Na | 0.9 | Cl | 3.0 |
| K | 0.8 | Br | 2.8 |
| Rb | 0.8 | I | 2.5 |
| Cs | 0.7 | At | 2.2 |
3.7.2 (a) Periodicity of Valence or Oxidation States (Detailed)
The valence of elements, often represented by their oxidation states, shows clear periodic trends, especially in their compounds with hydrogen and oxygen.
Periodic Trends in Valence (Table 3.9)
| Group | 1 | 2 | 13 | 14 | 15 | 16 | 17 |
|---|---|---|---|---|---|---|---|
| Number of valence electrons | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
| Valence | 1 | 2 | 3 | 4 | 3, 5 | 2, 6 | 1, 7 |
| Formula of hydride | LiH, NaH, KH | CaH₂ | B₂H₆, AlH₃ | CH₄, SiH₄, GeH₄, SnH₄ | NH₃, PH₃, AsH₃ | H₂O, H₂S, H₂Se, H₂Te | HF, HCl, HBr, HI |
| Formula of oxide | Li₂O, Na₂O, K₂O | MgO, CaO, SrO, BaO | B₂O₃, Al₂O₃, Ga₂O₃, In₂O₃ | CO₂, SiO₂, GeO₂, SnO₂, PbO₂ | N₂O₃, N₂O₅, P₄O₆, P₄O₁₀, As₂O₃, As₂O₅, Sb₂O₃, Sb₂O₅, Bi₂O₃ | SO₃, SeO₃, TeO₃ | Cl₂O₇ |
✨ Consolidated Periodic Trends ✨
This section summarizes the key periodic trends discussed, offering a quick visual reference for how properties change across periods and down groups.
Summary of Trends
Trends Across a Period (Left to Right)
Trends Down a Group (Top to Bottom)
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