General Science: Metals and Non-metals

📅 Topic: General Science (Chemistry)

This chapter is the backbone of Inorganic Chemistry questions in competitive exams. The questions here are usually factual, exception-based, or application-based (e.g., "Which alloy is used for soldering?"). Pay special attention to the "Exceptions" and "Alloys" sections—these are the favorite hunting grounds for examiners.

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1. Physical Properties (The Game of Exceptions)

General rules are easy: Metals are hard, shiny, and ductile. However, exams ask about the EXCEPTIONS. Memorize this list:

• Liquid Metal: Mercury (Hg) is the only metal liquid at room temperature.
• Liquid Non-Metal: Bromine (Br) is the only non-metal liquid at room temperature.
• Soft Metals: Lithium (Li), Sodium (Na), and Potassium (K) are soft enough to be cut with a knife.
• Lustrous Non-Metal: Iodine (I) has a metallic shine, even though it's a non-metal.
• Melting Point Anomalies:
  • Low: Gallium (Ga) & Caesium (Cs) melt on your palm.
  • High: Diamond (Carbon allotrope) is a non-metal but is the hardest natural substance.
• Conductivity Exception:
  • Graphite: A non-metal that is a good conductor of electricity.
  • Lead (Pb) & Mercury (Hg): Metals, but poor conductors of heat.

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2. Chemical Properties (How They React)

A. Amphoteric Oxides (High Yield Concept)

General Rule: Metal oxides are Basic. Non-metal oxides are Acidic.
The Exception: Amphoteric oxides react with BOTH acids and bases to produce salt and water.

B. Reaction with Water

• Violent Reaction: Sodium (Na) and Potassium (K) react so violently with cold water that the evolved Hydrogen catches fire. (Stored in Kerosene).
• Floaters: Calcium (Ca) and Magnesium (Mg) float because Hydrogen bubbles stick to them.
• Steam Only: Aluminium (Al), Iron (Fe), and Zinc (Zn) do not react with liquid water, only with Steam.
• No Reaction: Lead, Copper, Silver, Gold.

C. Aqua Regia (Royal Water)

Composition: Freshly prepared mixture of Concentrated Hydrochloric Acid (HCl) and Concentrated Nitric Acid (HNO₃).
Ratio: 3 : 1 (3 parts HCl, 1 part HNO₃).
Power: It can dissolve Gold and Platinum.

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3. Ionic Compounds

Formation: Transfer of electrons from a Metal (gives electron) to a Non-metal (takes electron). Example: NaCl.
Properties: Solid, Hard, High Melting Points.
Conductivity Trick: They conduct electricity in Molten or Aqueous state (ions are free), but NOT in solid state.

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4. Metallurgy: Extracting Metals

A. Important Processes

• Roasting: Heating Sulphide ores in Excess Air.
  Equation: 2ZnS + 3O₂ → 2ZnO + 2SO₂.
  Hint: Sulphide uses Roasting (sounds like roasting a chicken, needs air).
• Calcination: Heating Carbonate ores in Limited Air.
  Equation: ZnCO₃ → ZnO + CO₂.
  Hint: Carbonate uses Calcination.

B. The Thermit Reaction

Reaction: Iron(III) Oxide (Fe₂O₃) + Aluminium (Al) → Molten Iron.
Use: Joining railway tracks and cracked machine parts.
Reducing Agent: Aluminium.

C. Electrolytic Refining

Used for Copper, Zinc, Gold. The Anode is Impure Metal, and the Cathode is Pure Metal. Insoluble impurities settle as Anode Mud.

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5. Alloys and Corrosion (Everyday Application)

A. Corrosion & Galvanization

Rusting requires Air + Water. Galvanization prevents rust by coating Iron/Steel with a thin layer of Zinc.

B. Alloys (Memorize the Composition)

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6. Mentor’s Final Drill (Exam-Ready Questions)

Mentor’s Wisdom: Focus heavily on the Alloys table and the Exceptions in physical properties. These are "low-hanging fruit"—easy marks if you remember them.