CBSE Class 8 Science Notes Chapter 4 Materials: Metals and Non-Metals

Physical Properties of Metals:
Metals are:

• hard to touch.
• lustrous i.e., freshly Cut surfaces of metals have characteristic shining.
• malleable; the property of metals by which they can be beaten mW thin sheets is called malleability.
• ductile; the property of metal by which it can be drawn into wires is called ductility.
• sonorous i.e., metals produce ringing sound when struck on a hard surface.
• Good conductors of heat and electricity.

Metals like sodium and potassium are soft and can be cut with a knife.

Mercury is the only metal which is found in the liquid state at room temperature.

Physical Properties of Non-metals:

• Non-metals are soft and dull (e.g., coal and sulphur).
• Non-metals are generally brittle, i.e., they break down into a powdery mass on tapping with a hammer.
• They are not sonorous.
• They are poor conductors of heat and electricity.

Chemical Properties of Metals and Non-metals:
Reaction with Oxygen: Both metals and non-metals when burnt in oxygen from their oxides. Oxides of metals are basic in nature while that of non-metals are generally acidic in nature e.g.,

Reaction with Water: Some metals react with water to produce metal hydroxide and hydrogen gas. Generally, non-metals do not react with water.

Reaction with Acids: Metals react with dii. acids and produce metal salt and hydrogen gas. Generally, non-metals do not react with dil. acids.

Reaction with Bases: Metals react with bases to produce hydrogen gas.

Displacement Reaction: More reactive metals displace less reactive metals from their metal compounds in aqueous solutions.

Uses of Metals and Non-metals

• Metals are used in making machinery automobiles, aeroplanes. trains, satellites, industrial gadgets, cooking utensils, water boilers etc.
• Non-metals are also used in day-to-day life. Some examples are:
  • oxygen is essential for life.
  • nitrogen, phosphorus and potassium are used as fertilizers.
  • chlorine is used as a water purifier.

Atom: Atom is the smallest particle of matter which cannot be divided further by any physical means. Atoms are the basic units from which molecules and ions are formed.

Conductor: Substances which allow heat/electricity to pass through them are called conductors of heat/electricity

Displacement reaction: More reactive metals displace less reactive metals from their compounds in aqueous solutions.

Ductility: The property of metals by which they can be drawn into wires is called ductility

Elements: Substances whose molecules contain only one type of atoms are known as elements.

Hardness: Metals are hard, on the other hand, non-metals are generally brittle.

Malleability: The property of metals by which they can be beaten into thin sheets is called malleability.

Metals: The materials which are generally hard, lustrous, malleable, ductile, sonorous and good conductors of heat and electricity are called metals

Metalloids: Elements which possess characters of both metals and non-metals are called met.alloids.

Non-metals: Materials which are soft, dull in appearance, brittle, not sonorous and poor conductors of heat and electricity are called non-metals.

Sonorous: Metals are called sonorous because they produce a specific ringing sound.