Introduction to the Periodic Table

Introduction to the Periodic Table
Key concepts, historical background, and how to read the table

1. What Is the Periodic Table?

• A systematic arrangement of the 118 known chemical elements.
• Organized by atomic number (number of protons) → increasing left‑to‑right.
• Shows recurring (“periodic”) trends in physical and chemical properties.
• Serves as a roadmap for predicting element behavior, bonding patterns, and reactivity.

2. Historical Milestones

3. Layout of the Table

3.1 Periods (Rows)

• 7 horizontal periods (1–7).
• Each period corresponds to the filling of a principal electron shell (n = 1 to 7).
• As you move right, electrons fill higher‑energy subshells.

3.2 Groups (Columns)

• 18 vertical groups (numbered 1–18).
• Elements in the same group share valence‑electron configurations, leading to similar chemical behavior.
• Main groups: IA–VIIIA (1, 2, 13‑18) → “representative elements.”
• Transition metals: Groups 3–12.
• Lanthanides & actinides: f‑block placed below the main table.

3.3 Blocks

• s‑block: Groups 1‑2 (plus H & He). Outer electrons fill s‑orbitals.
• p‑block: Groups 13‑18. Outer electrons fill p‑orbitals.
• d‑block: Transition metals (Groups 3‑12). Outer electrons fill d‑orbitals.
• f‑block: Lanthanides & actinides. Outer electrons fill f‑orbitals.

4. Reading Element Information

Tip: The group number (for main‑group elements) often equals the number of valence electrons.

5. Periodic Trends