Periodic Classification of Elements: History & Modern Trends

The Periodic Table is the map of Chemistry. Understanding how elements are classified based on their electronic configuration is the first step to mastering Inorganic Chemistry for JEE and NEET.

1. Evolution of the Periodic Table

Before the modern table, several attempts were made to classify elements. While early attempts like Dobereiner's Triads and Newlands' Law of Octaves failed, Mendeleev's Periodic Table laid the groundwork by organizing elements by atomic mass and predicting undiscovered ones (e.g., Eka-Silicon).

Modern Periodic Law

In 1913, Henry Moseley proved that the physical and chemical properties of elements are periodic functions of their Atomic Number ($Z$), not atomic mass.

Mind map periodic classification of elements

Figure: Mind Map of Historical Development and Classification Systems

2. Classification of Elements (Blocks)

Elements are classified into four blocks based on the orbital into which the differentiating (last) electron enters.

s-Block (Groups 1 & 2)

Gen. Config: $ns^{1-2}$

Reactive metals, low IE.

p-Block (Groups 13-18)

Gen. Config: $ns^2 np^{1-6}$

Metals, non-metals & metalloids.

d-Block (Groups 3-12)

$(n-1)d^{1-10} ns^{0-2}$

Transition elements, variable valency.

f-Block (Inner Transition)

$(n-2)f^{1-14} (n-1)d^{0-1} ns^2$

Lanthanoids & Actinoids.

3. High-Yield Exam Concepts

IUPAC Naming for $Z > 100$

Roots: 0-nil, 1-un, 2-bi, 3-tri, 4-quad, 5-pent, 6-hex, 7-sept, 8-oct, 9-enn. Suffix: -ium.

104: Un-nil-quadium (Unq) - Rutherfordium
118: Un-un-octium (Uuo) - Oganesson

Diagonal Relationship

Elements of the 2nd period show similarities with elements of the 3rd period placed diagonally opposite. This is due to similar Ionic Potential (Charge/Size ratio).

$\text{Li} \leftrightarrow \text{Mg} \quad | \quad \text{Be} \leftrightarrow \text{Al} \quad | \quad \text{B} \leftrightarrow \text{Si}$

Periodic Properties and trends Class 11 chemistry