PRELIMS

Non-Metals and Their Compounds

In the modern periodic table, there are 24 non-metals (11 gases, 1 liquid - , and 12 solids). They are electronegative and poor conductors (except Graphite).

Hydrogen (H₂) and Its Isotopes

Hydrogen is the lightest gas and is known as a Rogue element (placed in Group 1 or 17).

• Isotopes:
  1. Protium ( ): Only isotope with zero neutrons.
  2. Deuterium ( ): Used as Heavy Water ( ) as a moderator in nuclear reactors.
  3. Tritium ( ): Radioactive isotope.
• Uses: Liquid hydrogen is used as high-efficiency rocket fuel.

Water ( ) and Hardness

1. Soft Water: Lathers easily with soap.
2. Hard Water: Contains bicarbonates, chlorides, and sulphates of Calcium and Magnesium.
   • Temporary Hardness: Due to Bicarbonates of Ca and Mg. Removed by Boiling or Clark’s Method (using Lime).
   • Permanent Hardness: Due to Chlorides and Sulphates of Ca and Mg. Removed by Soda Ash ( ) or Permutit process (Zeolite).

Oxygen, Nitrogen, and Phosphorus

• Oxygen ( ): Essential for life. Ozone ( ) is its allotrope that protects against UV rays.
• Nitrogen ( ): 78% of atmosphere. Haber’s Process is used for Ammonia ( ) synthesis.
  • Fixation: Conversion of atmospheric into nitrates by leguminous plants.
• Phosphorus ( ):
  • White Phosphorus: Highly reactive; kept under water. Used in rat poison.
  • Red Phosphorus: Less reactive; used in the match industry.
  • Black Phosphorus: Most stable allotrope; least reactive.
• Sulphur (S): Two common crystalline allotropes:
  • Rhombic Sulphur ( -sulphur): Stable below 96°C; yellow, brittle octahedral crystals.
  • Monoclinic Sulphur ( -sulphur): Stable above 96°C (the transition temperature); needle-shaped, amber crystals.

Halogens (Group 17)

1. Fluorine (F): Most electronegative and strongest oxidising agent. Used in for energy and Teflon (PTFE).
2. Chlorine (Cl): Used in PVC, bleaching powder, and mustard gas synthesis. Bleaches the color of flowers.
3. Bromine (Br): Only liquid non-metal. AgBr is used in photography.
4. Iodine (I): Used as antiseptic (Tincture of Iodine).

Inert Gases (Group 18)

Also called Noble gases: .

• Helium (He): Non-inflammable; used in balloons/weather indicators and artificial respiration ( ).
• Argon (Ar): Used in Arc welding and electric bulbs.
• Neon (Ne): Used in discharge tube glow lights (Neon signs).
• Radon (Rn): Heaviest gas; not found in the atmosphere.

UPSC Relevance

Non-metal chemistry explains several environmental and industrial phenomena.

• Hard Water: The chemical cause (Ca/Mg ions) and the methods of removal (Clark's vs Permutit) are standard GS-I/III basics.
• Inert Gases: Specific uses—like Helium for divers or Argon in welding—are favorite "Match the Following" options.
• Isotopes: Heavy water ( ) and its role as a moderator in India's nuclear reactors.