Chapter 3 Class 10 – Metals and Non-Metals
Introduction: Metals and Non-Metals?
- Metals: Elements that are good conductors of heat and electricity, and have a shiny appearance (luster). They are usually solid at room temperature (except mercury), malleable, and ductile.
- Example: Iron (Fe), Copper (Cu), and Aluminum (Al) are metals.
- Non-metals: These elements are poor conductors of heat and electricity and are usually non-lustrous. Most non-metals are gases at room temperature, and solids tend to be brittle.
- Example: Oxygen (O₂), Nitrogen (N₂), and Carbon (C) are non-metals.
Physical Properties of Metals
Metals exhibit the following characteristics:
Luster: Metals are shiny and reflective.
- Example: Silver (Ag) and Gold (Au) are shiny metals.
Malleability: Metals can be hammered into thin sheets.
- Example: Gold is so malleable that it can be hammered into very thin sheets, known as gold leaf.
Ductility: Metals can be drawn into wires.
- Example: Copper is used to make electrical wires due to its ductility.
Conduction: Metals conduct heat and electricity.
- Example: Copper is used in electrical wiring because it is an excellent conductor.
High Melting and Boiling Points: Most metals have high melting points.
- Example: Iron melts at 1538°C, which is very high compared to non-metals.
Physical Properties of Non-Metals
Non-metals have the following characteristics:
Dull Appearance: Non-metals do not have a shiny surface.
- Example: Sulfur (S) is a non-metal and is dull in appearance.
Brittleness: Non-metals are brittle and break or shatter easily when solid.
- Example: Phosphorus (P) is a brittle solid.
Poor Conductivity: Non-metals are poor conductors of heat and electricity.
- Example: Rubber is used for insulation because it is a poor conductor of electricity.
Low Melting and Boiling Points: Non-metals have low melting and boiling points compared to metals.
- Example: Oxygen has a boiling point of -183°C.
Exceptions in Physical Properties of Metals and Non-Metals
Mercury (Hg): The only metal that is liquid at room temperature.
- Example: Mercury is used in thermometers because it remains liquid at room temperature.
Graphite (C): A non-metal that is a good conductor of electricity.
- Example: Graphite is used in pencils and as an electrode in electrolysis.
Sodium (Na) and Potassium (K): Soft metals that can be cut with a knife.
- Example: Sodium is soft enough to be cut with a knife and reacts explosively with water.
Chemical Properties of Metals
Metals react with various substances to form compounds:
Reaction with Oxygen: Metals react with oxygen to form oxides.
- Example: 4Fe + 3O₂ → 2Fe₂O₃ (Iron reacts with oxygen to form iron oxide, or rust).
Reaction with Water: Some metals react with water to produce hydrogen gas.
- Example: 2Na + 2H₂O → 2NaOH + H₂ (Sodium reacts with water to form sodium hydroxide and hydrogen gas).
Reaction with Acids: Metals react with acids to release hydrogen gas.
- Example: Zn + 2HCl → ZnCl₂ + H₂ (Zinc reacts with hydrochloric acid to form zinc chloride and hydrogen gas).
Displacement Reaction: A more reactive metal displaces a less reactive metal from its compound.
- Example: Zn + CuSO₄ → ZnSO₄ + Cu (Zinc displaces copper from copper sulfate solution).
Uses of Metals and Non-Metals
Metals:
- Iron (Fe): Used in construction (e.g., steel beams, bridges) and machinery.
- Copper (Cu): Used for electrical wiring due to its excellent conductivity.
- Aluminum (Al): Used in making aircraft bodies, due to its light weight and strength.
Non-Metals:
- Oxygen (O₂): Essential for respiration in living organisms.
- Carbon (C): Used in the manufacture of steel and as a fuel source (charcoal).
- Nitrogen (N₂): Used in the production of fertilizers.
Reactivity Series
The reactivity series is a list of metals arranged in order of their reactivity. More reactive metals tend to displace less reactive metals in chemical reactions.
- Example: Potassium (K) and Sodium (Na) are highly reactive and placed at the top of the reactivity series. Gold (Au) and Platinum (Pt) are at the bottom due to their low reactivity.
Ionic and Covalent Bonds
Ionic Bond: Formed when electrons are transferred from one atom to another, resulting in positive and negative ions that attract each other.
- Example: NaCl (Sodium chloride) is formed by the ionic bonding between sodium (Na) and chlorine (Cl).
Covalent Bond: Formed when two atoms share electrons to achieve stability.
- Example: H₂O (Water) is formed by covalent bonding between hydrogen (H) and oxygen (O) atoms.
Minerals and Ores
Minerals: Naturally occurring substances from which metals are extracted. For example, bauxite is a mineral from which aluminum is extracted.
Ores: Minerals that contain a sufficiently high concentration of metal to be economically extracted. For example, hematite (Fe₂O₃) is an ore of iron.
Extraction of Metals
Metals are extracted from their ores by various methods:
Roasting and Smelting: Used to extract metals like iron from their ores.
- Example: Iron ore (Fe₂O₃) is roasted in the presence of coke to produce iron.
Electrolytic Reduction: Used for extracting metals like aluminum.
- Example: Aluminum is extracted from its ore bauxite using electrolysis.
Refining: After extraction, metals are purified using methods like electrolysis.
- Example: Copper is purified by electrolysis.
Corrosion
Corrosion is the gradual degradation of metals due to chemical reactions with the environment, especially oxygen and moisture.
- Example: Rusting of iron is a common form of corrosion, where iron reacts with water and oxygen to form iron oxide (rust).
- Reaction: 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃ (Rust is formed).
Prevention of Corrosion:
- Painting: Applying a coat of paint prevents air and moisture from coming into contact with the metal.
- Example: Bridges and iron gates are painted to prevent rusting.
- Galvanization: Coating metals like iron with a layer of zinc to prevent corrosion.
- Example: Zinc-coated iron sheets (galvanized iron) are used in roofing.