Science Class 8th Chapter 4 : Materials: Metals and Non-Metals

 

Science Class 8^th

Chapter 4 Materials: Metals and Non-Metals

1.            Physical Properties: these properties are associated with physical appearance.

# Metals

• ·     Malleability: The property of metals by which they can be beaten into thin sheets.
• ·      Ductility: The property of metals by which they can be drawn into thin wires.
• ·      Sonorous: The word ‘sonorous’ is meant to be sound producing. As the metals produce ringing sound, thus they are said to be sonorous.
• ·      Lustrous: The word ‘lustrous’ is meant to be shiny surface. As surface of metal is shiny naturally without any polish, thus they are said to lustrous.
• ·      Good Conductor of heat and electricity: Metals can easily pass heat and electricity because they are good conductor of heat and electricity.

# Non-Metals

·     Less malleable

·     Less ductile

·      Sonorous but do not produce ringing sound.

·      Non lustrous without any polishing.

·      Bad conductor of heat and electricity.

 

1.            Chemical Properties: these properties are associated with chemical composition.

# Metals

·     Reaction with oxygen: Metals reacts with oxygen to form metal oxide.

Fe + O₂  → 2FeO + H₂

·     Reaction with water: Metals reacts with water to form metal hydroxide and hydrogen.                                                                                               

2Fe + 2H₂O → 2FeOH + H₂

·     Reaction with acid: Metals reacts with acid to form salt and hydrogen.

Fe + 2HCl → FeCl₂ +H2                                                                                            

# Non-Metals

·     Reaction with oxygen: Non-Metals reacts with oxygen to form non-metal oxide.

 N₂   +   O₂ → 2NO₂ 

_·       Reaction with water: Non-Metals do not react with water, but in some cases they are kept emerged in water to avoid any reaction.

For ex: Phosphorous is highly reactive non-metals, it catches fire immediately as it came in contact with air. Therefore, it is kept immersed in water to avoid reaction.

·     Reaction with acid: Non-Metals generally do not react with acid. 

·     Reaction with bases:   Non-metals reacts with base to form salt and hydroxide.

# Displacement Reaction: In displacement reaction, more reactive metal displaces lesser reactive metal from its place.

Copper Sulphate (CuSO₄) + Zinc (Zn) → Zinc Sulphate(ZnSO₄) + Copper (Cu)

 

1.            Uses of Metals and Non-metals

Metals	Non-metals
Machinery	To breath
Automobiles	Make fertilizers
Utensils	Water purification
Industrial gadgets	Applied on wounds as an antiseptic
Water boilers	Fire crackers

 

Ø     Metalloids are the substances which possess properties of both metal and non-metals.