METAL &
NON-METAL:
1. All the materials found in the
earth's crust are made up of chemical elements.
2. All these elements can be broadly
divided into two classes:
Metals and Non-metals.
Note : Out of 117 elements 83 are naturally occuring. Out of total
117 elements about 24 are non-metals and rest are metals.
3. Physical
Properties of Metals
• Metals, in their pure state,
possess a shining surface(metallic lustre). Freshly cut metals have a bright
metallic lustre.
• Metals are solid at room
temperature. Mercury is the only metal that is liquid at room temperature.
• Metals are generally hard and
strong. But metals like sodium and potassium are exceptionally very soft and
can be cut with a knife.
• Metals have high melting and
boiling points. Sodium,potassium, gallium and mercury have low melting and
boiling points.
• Metals are good conductors of
heat. Silver, followed by copper and aluminium, is the best conductor of heat.
These days, cooking vessels and other utensils are made up of copper and
aluminium.
• Metals are also good conductors of
electricity. Silver, followed by copper, gold and aluminium, is the
bestconductor of electricity. Copper and aluminium are used for making
electrical wires.
• Metals are sonorous. They make a
ringing sound when struck.
• Metals are usually malleable. They
can be hammered into thin sheets and rolled into different shapes without
breaking. Gold and silver are the most malleable metals.
• Metals are generally ductile. They
can be easily drawn into wires. Gold and silver are most ductile metals. Copper
wires are used for electrical purposes.
• Metals have high tensile strength,
i.e. they can hold heavy loads without breaking.
• Metals have high densities i.e.
they are heavy in nature. Sodium and potassium metals are exceptions as they
have low densities and float on water.
4. Corrosion is the process of
slowly eating away of metal due to attack of atmospheric gases and water on the
surface of metal. The most common example of corrosion is the rusting of iron.
Rusting: Rusting is the corrosion of iron on exposure to atmosphere
Non-metals are quite abundant in
nature. They are main constituent of atmosphere.
• Oxygen, nitrogen and noble gases
are present in the air.
• Non-metals are also present in
large amounts in oceans.
• Hydrogen and oxygen are present as
water and chlorine is present as chlorides in the oceans.
• Oxygen, silicon, phosphorus and
sulphur are present in the earth's crust.
6. Physical
Properties of Non-metals:
• Non-metals are either solids or
gases at room temperature. Bromine is the only liquid non-metal at room
temperature.
• Non-metals are soft. Phosphorus is
so soft that can be cut with a knife. Diamond, an allotrope of carbon, is the
hardest known substance.
• Non-metals have low tensile
strength, i.e. they are not strong and break easily.
• Non-metals are non-lustrous and
have a dull appearance. Graphite, an allotrope of carbon and iodine have
shining lustrous surfaces.
• Non-metals are non-malleable and
non-ductile. They cannot be hammered into sheets or drawn into wires. These are
brittle solids. When non-metals like sulphur, are hammered or stretched, they
break into pieces.
• Non-metals are non-conductors or
bad conductors of heat and electricity. Gas carbon and graphite are good
conductors of heat and electricity.
• Non-metals are non-sonorous i.e.
do not make a ringing sound when struck.
• Non-metals usually have low
densities
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