CBSE Class 10 Science Metals & Non Metals Quick Revision for Board Exams

With the CBSE Class 10 Science Board Exam approaching, students must focus on revising high-weightage and concept-based chapters efficiently. Metals and Non-Metals is an important chapter that frequently contributes to short-answer, long-answer, and case-based questions in the board paper.

Here is a quick revision guide to help students recap important concepts, equations, and commonly asked questions in a structured manner, ensuring confidence and accuracy in the final board exam.

Properties of Metals and Non-metals

Metals and non-metals are fundamental elements, classifying substances based on distinct physical and chemical characteristics.

Metals and non-metals exhibit contrasting physical properties. The properties of non-metals are generally the direct opposite of metals. Here is a basic difference between Metals and Non-metals:

Chemical Properties of Metals

Chemically, metals are known as electropositive elements because they form positive ions (cations) by losing electrons. For example, Sodium (Na) readily loses one electron to form a stable Na⁺ ion.

Reaction of Metal with Oxygen

• General Reaction: Metal + Oxygen → Metal Oxide

• Reactivity Variation:

• High Reactivity: Metals like sodium (Na) and potassium (K) react violently with oxygen at room temperature, often catching fire.

• Moderate Reactivity: Metals like magnesium (Mg) and zinc (Zn) require strong heating to react with oxygen.

• Low Reactivity: Metals like iron (Fe) and copper (Cu) require prolonged, strong heating to react.

Nature of Metal Oxides

Metal oxides are typically basic in nature. Some metal oxides exhibit both acidic and basic properties; these are called amphoteric oxides. Key examples include Aluminium oxide (Al₂O₃) and Zinc oxide (ZnO).

Reaction of Metal with Water

• General Reaction: Metal + Water → Metal Hydroxide OR Metal Oxide + Hydrogen Gas (H₂)

• The reaction's intensity and product depend on the metal's reactivity and water temperature.

• Cold Water:

• Sodium (Na) & Potassium (K): React violently, producing enough heat to ignite the hydrogen gas evolved.

• Hot Water:

• Magnesium (Mg) reacts with hot water to form magnesium hydroxide and hydrogen gas.

• Steam: Aluminium (Al), Zinc (Zn), & Iron (Fe) react only with steam, forming metal oxide (not hydroxide).

• No Reaction: Metals low in the reactivity series (e.g., copper (Cu), silver (Ag), and gold (Au)) do not react with water or steam.

(Memory Tip: When a metal reacts with liquid water (cold or hot), it forms a metal hydroxide. When a metal reacts with steam (gaseous water), it forms a metal oxide.)

Reaction of Metals with Salt Solutions (Displacement Reaction)

Principle: A more reactive metal will displace a less reactive metal from its salt solution. This is determined by the metal's position in the reactivity series.

Example: Zn (s) + CuSO₄ (aq) → ZnSO₄ (aq) + Cu (s) (Zinc is more reactive than Copper).

No Reaction Case: Cu (s) + ZnSO₄ (aq) → No Reaction (Copper is less reactive than Zinc).

(Memory Tip: A more reactive metal kicks a less reactive metal out of its salt solution.)

Chemical Properties of Non-metals

Chemically, non-metals are known as electronegative elements because they form negative ions (anions) by gaining electrons. For instance, Chlorine (Cl) readily gains one electron to form a stable Cl⁻ ion.

Reactions of Non-metals

• Reaction with Oxygen: Non-metal + Oxygen → Non-metallic Oxide. These oxides are either acidic or neutral (e.g., Carbon Monoxide (CO) is neutral, Carbon Dioxide (CO₂) is acidic).

• Reaction with Water: Non-metals do not react with water.

• Reaction with Acids: Non-metals do not react with acids.

• Reaction with Salt Solutions: A more reactive non-metal displaces a less reactive non-metal from its salt solution (e.g., 2NaBr (aq) + Cl₂ (g) → 2NaCl (aq) + Br₂ (l)).

How Metals and Non-metals React: Ionic Bonding

Metals and non-metals react through the transfer of electrons. A metal atom loses its valence electron(s) to become a positively charged ion (cation). A non-metal atom gains these electron(s) to complete its valence shell and become a negatively charged ion (anion).

 The strong electrostatic force of attraction between the oppositely charged cation and anion forms an ionic bond, resulting in an ionic compound.

Properties of Ionic Compounds

• Physical Nature: Ionic compounds are solids and generally hard due to strong electrostatic forces of attraction between ions.

• Melting and Boiling Points: They have high melting and boiling points because significant energy is required to overcome these strong inter-ionic forces.

• Solubility: Generally soluble in polar solvents like water but insoluble in non-polar solvents.

• Conduction of Electricity:

• Solid State: They do not conduct electricity because ions are held in fixed positions.

• Molten or Aqueous State: They conduct electricity because the ions become free to move and carry charge.

Occurrence of Metals and Introduction to Metallurgy

Metals are found in two primary states:

1. Free State (Native State): Found as the pure element (e.g., gold, platinum); common for less reactive metals.

2. Combined State: Found as compounds (e.g., oxides, sulfides); common for moderately and highly reactive metals.

Key Terminology in Metallurgy

• Minerals: Naturally occurring elements or compounds in the Earth's crust.

• Ores: Minerals from which a metal can be extracted profitably.

• Gangue: Unwanted impurities (sand, soil) mixed with the ore.

• Concentration (or Enrichment) of Ore: The process of removing gangue from the ore.

Extraction of Metals

The method of metal extraction depends on its position in the reactivity series. The process generally follows: Concentration of Ore → Conversion to Oxide → Reduction to Metal → Refining.

Extracting Metals of Medium Reactivity (e.g., Zn, Fe)

1. Ore Type: Typically sulfide or carbonate ores.

2. Conversion to Oxide: Easier to reduce an oxide.

• Roasting: For sulfide ores; heated in excess air.

• Calcination: For carbonate ores; heated in limited or no air.

3. Reduction to Metal: Metal oxide reduced using carbon (coke) as a reducing agent.

Extracting Metals of Low Reactivity (e.g., Hg, Cu)

1. Ore Type: Often sulfide ores.

2. Roasting: Sulfide ore heated in air to convert it to an oxide.

3. Reduction to Metal: The metal oxide is then reduced to the metal by simple heating; no additional reducing agent is needed.

Extracting Metals of High Reactivity (e.g., Na, K, Al)

1. Challenge: These metals are very reactive, and their compounds are stable, making carbon reduction ineffective.

2. Method: Electrolytic Reduction (Electrolysis) is used. The metal is extracted by the electrolysis of its molten chloride or oxide. For example, in molten NaCl electrolysis, Na⁺ ions are reduced to Na metal at the cathode.

A Note on Refining: Electrolytic Refining

This method purifies crude metals. The impure metal is the anode, a thin strip of pure metal is the cathode, and a salt solution of the metal serves as the electrolyte. During electrolysis, pure metal deposits onto the cathode.

Corrosion

Definition: The gradual deterioration of a metal surface due to the action of air, moisture, or other chemicals.

Examples:

• Silver: Forms a black coating of silver sulfide.

• Copper: Forms a green coating of basic copper carbonate.

• Iron: Acquires a reddish-brown flaky coating called rust (rusting).
  Prevention of Corrosion:

• Painting, oiling, greasing.

• Galvanization: Coating iron/steel with a thin layer of zinc.

• Anodizing: Creating a thick, protective oxide layer (e.g., on aluminum).

• Alloying: Mixing metals with other elements to improve properties, including corrosion resistance.