Electronic Configurations and Types of Elements

🔹 Group Electronic Configurations

Elements in the same group have similar valence shell configurations and properties. Example: Group 1 (alkali metals) all have ns1 configuration:

  • Li: 1s22s1
  • Na: 1s22s22p63s1
  • K: [Ar]4s1

🔹 Four Blocks of Elements

Elements are classified based on which atomic orbitals are being filled:

1️⃣ s-Block Elements

  • Groups 1-2
  • Outer configuration: ns1 (Group 1) or ns2 (Group 2)
  • Highly reactive metals ⚡
  • Form +1 or +2 ions easily
  • Reactivity ↑ down the group

2️⃣ p-Block Elements

  • Groups 13-18
  • Outer configuration: ns2np1 to ns2np6
  • Includes metals, non-metals, metalloids
  • Non-metallic character ↑ left → right
  • Group 18 (noble gases) have stable ns2np6 config

3️⃣ d-Block Elements (Transition Metals)

  • Groups 3-12
  • General configuration: (n-1)d1-10ns0-2
  • Form colored ions 🎨
  • Show variable valence
  • Often act as catalysts
  • Exception: Zn, Cd, Hg don’t show typical transition properties

4️⃣ f-Block Elements (Inner Transition)

  • Lanthanoids (Ce-Lu) & Actinoids (Th-Lr)
  • Configuration: (n-2)f1-14(n-1)d0-1ns2
  • Actinoids are radioactive ☢️
  • Elements after uranium are transuranium

🔹 Special Cases

  • Helium (s-block) placed in p-block due to noble gas properties
  • Hydrogen placed separately (can behave like Group 1 or Group 17)

🔹 Metals, Non-Metals, Metalloids

  • Metals (left side):
    • Good conductors 🔌
    • Malleable/ductile
    • High melting points (mostly)
  • Non-Metals (top-right):
    • Poor conductors
    • Brittle
  • Metalloids (along zig-zag line):
    • Show mixed properties (e.g., Si, Ge, As)

🔹 Periodic Trends

Metallic character:
• ↑ down a group
• ↓ left → right in a period
Example: P < Si < Be < Mg < Na (increasing metallic character)

📌 NEET Important Concepts

  1. Block classification based on electron filling order (s,p,d,f)
  2. Exceptional cases: He position & H behavior
  3. Transition metals vs. inner transition metals
  4. Periodic trends in metallic character
  5. Properties of metals/non-metals/metalloids

💡 Practice Problems

Q1: Why are there 18 elements in Period 5?
Ans: Orbitals filled: 5s (2e–), 4d (10e–), 5p (6e–) → Total 18 electrons.

Q2: Where would element Z=120 be placed?
Ans: Group 2 (alkaline earth metals), configuration: [Uuo]8s2