Classification of Elements and Periodicity

Master the periodic table, periodic trends, and element properties for JEE Chemistry.

Understanding the periodic table and periodic trends is essential for predicting chemical behavior and solving JEE problems.

Overview

graph TD
    A[Periodic Classification] --> B[Modern Periodic Law]
    A --> C[Periodic Trends]
    A --> D[Block Classification]
    C --> C1[Atomic Radius]
    C --> C2[Ionization Energy]
    C --> C3[Electronegativity]
    D --> D1[s-block]
    D --> D2[p-block]
    D --> D3[d-block]
    D --> D4[f-block]

Modern Periodic Law

Properties of elements are a periodic function of their atomic number.

Block Classification

BlockElementsValence Electrons
s-blockGroups 1, 2ns¹⁻²
p-blockGroups 13-18ns²np¹⁻⁶
d-blockGroups 3-12(n-1)d¹⁻¹⁰ns⁰⁻²
f-blockLanthanoids, Actinoids(n-2)f¹⁻¹⁴

Atomic Radius

Across Period (→): Decreases (increasing Zeff)

Down Group (↓): Increases (new shells added)

Order: Li > Be > B > C > N > O > F

Ionic Radius

  • Cations < Parent atom (lose electrons)
  • Anions > Parent atom (gain electrons)
  • Isoelectronic species: Higher Z → smaller radius

Ionization Energy

Energy required to remove an electron from isolated gaseous atom.

Across Period (→): Generally increases

Down Group (↓): Decreases

Anomalies:

  • Be > B (due to penetration of 2s)
  • N > O (half-filled stability)
$$\boxed{IE_1 < IE_2 < IE_3 < ...}$$

Electron Affinity

Energy released when electron is added to gaseous atom.

Across Period (→): Generally increases (more negative)

Down Group (↓): Generally decreases

Anomaly: Cl > F (small size of F causes repulsion)

Electronegativity

Tendency to attract shared electrons.

Pauling Scale: F = 4.0 (highest)

Across Period (→): Increases

Down Group (↓): Decreases

Metallic Character

Across Period (→): Decreases

Down Group (↓): Increases

Chemical Reactivity

  • Metals: More reactive down the group
  • Non-metals: More reactive up the group

Diagonal Relationship

Elements diagonally related show similar properties:

  • Li ~ Mg
  • Be ~ Al
  • B ~ Si

Due to similar charge/radius ratio.

JEE Tip
Most periodic trends can be explained by effective nuclear charge (Zeff) and distance from nucleus.

Practice Problems

  1. Arrange in increasing order of first ionization energy: Na, Mg, Al, Si, P

  2. Which has the largest ionic radius: O²⁻, F⁻, Na⁺, Mg²⁺?

  3. Explain why nitrogen has higher ionization energy than oxygen.

Quick Check
Why do noble gases have very high ionization energies?

Further Reading