Class 8 Notes: Metals and Non-Metals CBSE

Class 8 Notes: Metals and Non-Metals

Elements

Definition: ⇒ An element is a pure substance from which it cannot be purified by any physical or chemical method.

eg: - Oxygen (O), Hydrogen (H), Carbon (C).

➥ The smallest unit of an element is atom.

➥ Chemists have discovered 118 elements.

Classification of Elements

1. Metals:

➥ Metal is a solid material that conducts heat and electricity, hard, shiny, malleable, ductile and sonorous. (except mercury).

Physical Properties:

1. Malleability: Ability to be hammered into thin sheets.
   • eg:- Gold is malleable.
2. Ductility: Ability to be drawn into thin wires.
   • eg: - Copper is ductile.
3. Lustre: Shiny appearance or the ability to reflect light.
   • eg: - Silver has a high lustre.
4. Sonorous: Ability to produce a ringing sound when struck.
   • eg: - Bell metal is sonorous.
5. Electrical Conductivity: Ability to conduct electricity.
   • eg: - Copper conducts electricity.

Chemical Properties with Examples:

1. Reaction of Metal with Oxygen:
   • Magnesium reacts with oxygen to form magnesium oxide:
     2Mg + O₂ → 2MgO
   • Iron reacts with oxygen to form iron(III) oxide:
     4Fe + 3O₂ → 2Fe₂O₃
2. Reaction of Metal with Water:
   • Sodium reacts with water to form sodium hydroxide and hydrogen gas:
     2Na + 2H₂O → 2NaOH + H₂
   • Calcium reacts with water to form calcium hydroxide and hydrogen gas:
     Ca + 2H₂O → Ca(OH)₂ + H₂
3. Reaction of Metal with Acid:
   • Zinc reacts with hydrochloric acid to form zinc chloride and hydrogen gas:
     Zn + 2HCl → ZnCl₂ + H₂
   • Magnesium reacts with sulfuric acid to form magnesium sulfate and hydrogen gas:
     Mg + H₂SO₄ → MgSO₄ + H₂
4. Reaction of Metal with Salt:
   • Iron reacts with copper sulfate to form iron sulfate and copper:
     Fe + CuSO₄ → FeSO₄ + Cu
   • Lead reacts with copper chloride to form lead chloride and copper:
     Pb + CuCl₂ → PbCl₂ + Cu

Types of Metals

Ferrous Metals

➥ The metals which contain iron are called ferrous metals.

➥ The are directly attracted by magnets.

eg: - cast iron, wrought iron, carbon steel, stainless steel etc.

Non-Ferrous Metals

➥ The metals which do not contain iron are called non-ferrous metals.

➥ The are not attracted by magnets.

eg: - Aluminium, copper, zinc, tin lead .. etc.

Occurrence of Metals

In Nature: Metals are found in the Earth's crust, often combined with other elements in ores.

Extraction: Metals are extracted from their ores through processes like smelting and electrolysis.

Noble Metals and Their Uses

➥ Noble metals are metals that are resistant to corrosion and oxidation in moist air.

eg: - Gold (Au), Silver (Ag), Platinum (Pt).

Uses: Jewelry, currency, electronics due to their durability and conductivity.

2. Non-Metals

➥ Poor conductors of heat and electricity, can be solid, liquid, or gas at room temperature.

Occurrence of Non-Metals

In Nature: Non-metals are found in various forms, from gases (e.g., Oxygen) to solids (e.g., Sulfur).

Physical Properties of Non- Metals:

1. Low Density: Non-metals are generally less dense than metals.
   eg:- Helium is less dense than iron.
2. Brittle: Non-metals tend to break or shatter easily when subjected to force.
   eg: - Graphite in pencils breaks into small pieces.
3. Poor Conductivity: Non-metals do not conduct electricity or heat well.
   eg:- Sulphur is a poor conductor of electricity.
4. Low Melting and Boiling Points: Non-metals generally have lower melting and boiling points compared to metals.
   eg:- Carbon (graphite) melts at around 3700°C.
5. Dull Appearance: Most non-metals have a dull or matte appearance.
   eg:- Phosphorus appears dull and waxy.

Chemical Properties of Non- Metals:

1. Non-metals are electronegative in nature.
2. React with Oxygen:
   • Sulfur reacts with oxygen to form sulfur dioxide:
     S + O₂ → SO₂
   • Carbon reacts with oxygen to form carbon dioxide:
     C + O₂ → CO₂
3. React with Water: Non-metals do not react with water
4. React with Acid:
   • Phosphorus reacts with nitric acid to form phosphoric acid and nitrogen dioxide:
     P + 5HNO₃ → H₃PO₄ + 5NO₂ + H₂O
   • Carbon does not react with dilute acids, but concentrated nitric acid oxidizes it to carbon dioxide:
     C + 4HNO₃ → CO₂ + 4NO₂ + 2H₂O

Purity of Gold

➥ Gold purity is measured in carats (24-carat gold is pure gold).

Uses: Jewelry, investment, and industrial applications due to its resistance to corrosion and malleability.

Alloy

➥ An alloy is a mixture of metals or a metal combined with other elements.

eg:- Brass (Copper and Zinc), Bronze (Copper and Tin).

Uses: Increased strength, durability, and specific properties for various applications.

Corrosion

➥ Corrosion is when metals slowly get damaged because they react with things like oxygen, water, or chemicals in the environment.

eg: - 4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃

Preventionof Corrosion:

1. By usingOil Paint and Grease: Applying oil-based paints or greases to create a barrier against moisture and corrosive substances.
2. Electroplating: Coating a metal object with a thin layer of another metal using electrolysis to prevent corrosion and enhance appearance.
3. Alloying: Mixing a metal with other elements to form alloys that are more resistant to corrosion than pure metals.
4. Galvanization: Coating iron or steel with a layer of zinc to protect against corrosion by sacrificial protection.
5. Anodizing: Creating an oxide layer on the surface of metals (like aluminum) through electrolytic passivation to enhance corrosion resistance.
6. Tinning: Coating iron or steel with a thin layer of tin to prevent corrosion and improve solderability.

---

---