notes for metals and non metals class 8
Answers
At cathode (reduction) – equivalent amount of metal from solution is deposited
Impurities deposit at the bottom of the anode.
Metals
Metals are described as chemical elements that readily lose valence electrons to form positive ions (cations).
Examples: Aluminium, copper, iron, tin, gold.
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Physical Properties
Physical Properties of Nonmetals
Occur as solids, liquids, and gases at room temperature
Brittle
Non-malleable
Non-ductile
Non-sonorous
Bad conductors of heat and electricity
Exceptions in Physical Properties
Alkali metals (Na, K, Li) can be cut using a knife.
Mercury is a liquid metal.
Lead and mercury are poor conductors of heat.
Mercury expands significantly for the slightest change in temperature.
Gallium and cesium have a very low melting point
Iodine is non-metal but it has lustre.
Graphite conducts electricity.
Diamond conducts heat and has a very high melting point.
Physical Properties of Metals
● Hard and have a high tensile strength
● Solids at room temperature, except mercury, which is liquid at room temperature.
● Sonorous
● Good conductors of heat and electricity
● Malleable, i.e., can be beaten into thin sheets
● Ductile, i.e., can be drawn into thin wires
● High melting and boiling points (except Cesium (Cs) and Gallium (Ga))
● Dense, (except alkali metals). Osmium – highest density and lithium – least density
● Lustrous
● Silver-grey in colour, (except gold and copper)
Non-Metals
Non-metals are those elements, which do not exhibit the properties of metals.
Examples: Carbon, Boron etc.
Chemical Properties of Metals
● Alkali metals (Li, Na, K, etc) react vigorously with water and oxygen or air.
● Mg reacts with hot water.
● Al, Fe, and Zn react with steam.
● Cu, Ag, Pt, Au do not react with water or dilute acids.
Chemical Properties
Displacement Reactions
A more reactive element displaces a less reactive element from its compound or solution.
i) Zn(s)+CuSO4(aq)→ZnSO4(aq)+Cu(s)
ii) 2Al(s)+Fe2O3(molten)→Al2O3(s)+2Fe(molten)
Metals Reaction with Oxygen (Burnt in Air)
Metal + Oxygen → Metal oxide (basic)
● Na and K are kept immersed in kerosene oil as they react vigorously with air and catch fire.
4K(s)+O2(g)→2K2O(s) (vigorous reaction)
● Mg, Al, Zn, Pb react slowly with air and form a protective layer that prevents corrosion.
2Mg(s)+O2(g)→2MgO(s) (Mg burns with a white dazzling light)
4Al(s)+3O2(g)→2Al2O3(s)
● Silver, platinum, and gold don’t burn or react with air.
Reaction of Metals with Water/Steam
Metal+Water→Metal hydroxide or Metal oxide+Hydrogen
Extraction of Metals and Non-Metals
Applications of Metals and Non-metals
Zinc is used to protect the iron from rusting.
Gold and silver are used for making jewellery.
Oxygen is used by plants and animals.
For the preparation of ammonia, nitric acid and fertilizers, nitrogen is used.
For the purification of water, chlorine is used.
Diamonds are used for cutting glass in different industries.
Occurrence of Metals
Most of the elements especially metals occur in nature in the combined state with other elements. All these compounds of metals are known as minerals. But out of them, only a few are viable sources of that metal. Such sources are called ores.
Roasting
Roasting:- Converts sulfide ores into metal oxides on heating strongly in the presence of excess air.
It also removes volatile impurities.
2ZnS(s)+3O2(g)+Heat→2ZnO(s)+2SO2(g)
Calcination
Calcination: Converts carbonate and hydrated ores into oxides on heating strongly in the presence of limited air. It also removes volatile impurities.
ZnCO3(s)+heat→ZnO(s)+CO2(g)
CaCO3(s)+heat→CaO(s)+CO2(g)
Refining of Metals
Refining of metals – removing impurities or gangue from crude metal. It is the last step in metallurgy and is based on the difference between the properties of metal and the gangue.
Electrolytic Refining
The process of purifying impure metal to obtain pure metal on the passage of electric current is called electrolytic refining.
Metals like copper, zinc, nickel, silver, tin, gold etc., are refined electrolytically.
Anode – impure or crude metal
Cathode – a thin strip of pure metal
Electrolyte – aqueous solution of a metal salt From anode (oxidation) – metal ions are released into the solution
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