Introduction
Everything around us is made up of elements. These elements
are broadly classified into two categories:
- Metals
- Non-metals
Metals play a major role in our daily life. From cooking
utensils and electric wires to vehicles and buildings, metals are used
everywhere because of their special properties. Non-metals are equally
important and are used in respiration, fertilizers, medicines, fuels and many
industrial processes.
The classification of elements into metals and non-metals is
based mainly on their physical and chemical properties.
PHYSICAL PROPERTIES OF METALS
1. Metallic Lustre
Metals in their pure form have a shiny surface. This
property is called metallic lustre.
Examples
- Gold
- Silver
- Copper
- Aluminium
When metals are rubbed with sandpaper, the shining surface
becomes visible again because the oxide layer is removed.
2. Malleability
The property by which metals can be beaten into thin sheets
is called malleability.
Examples
- Aluminium
foils
- Silver
foil
- Gold
foil
Important Fact
Gold and silver are the most malleable metals.
3. Ductility
The property by which metals can be drawn into thin wires is
called ductility.
Examples
- Copper
wires
- Aluminium
wires
Important Fact
Gold is the most ductile metal.
A wire nearly 2 km long can be drawn from just 1 gram of
gold.
4. Hardness
Most metals are hard.
Examples
- Iron
- Copper
- Zinc
However, some metals like sodium and potassium are soft and
can be cut with a knife.
5. Conductivity of Heat
Metals are good conductors of heat.
Best Conductors
- Silver
- Copper
Poor Conductors
- Lead
- Mercury
This is why cooking utensils are made from metals like
aluminium and copper.
6. Conductivity of Electricity
Metals allow electric current to pass through them.
Examples
- Copper
- Aluminium
That is why electric wires are made of metals.
The outer covering of electric wires is made of PVC or
rubber because these substances are poor conductors of electricity and protect
us from electric shocks.
7. Sonority
Metals produce a ringing sound when struck with a hard
object. This property is called sonority.
Example
School bells are made of metals because they produce sound
on striking.
PHYSICAL PROPERTIES OF NON-METALS
Non-metals generally show properties opposite to metals.
Examples of Non-metals
- Carbon
- Sulphur
- Oxygen
- Nitrogen
- Hydrogen
- Iodine
General Properties of Non-Metals
|
Property |
Non-metals |
|
Lustre |
Generally dull |
|
Malleability |
Non-malleable |
|
Ductility |
Non-ductile |
|
Conductivity |
Poor conductors |
|
Sonority |
Non-sonorous |
Exceptions in Physical Properties
1. Mercury
Mercury is a metal but exists as a liquid at room
temperature.
2. Iodine
Iodine is a non-metal but has lustre.
3. Graphite
Graphite is a non-metal but conducts electricity.
4. Diamond
Diamond is a form of carbon and is the hardest natural
substance.
5. Sodium and Potassium
These metals are very soft and can be cut with a knife.
CHEMICAL PROPERTIES OF METALS
1. Reaction of Metals with Oxygen
Most metals react with oxygen to form metal oxides.
General Reaction
Magnesium Burning in Air
Magnesium burns with a dazzling white flame to form
magnesium oxide.
Observation
- Bright
white flame
- White
ash formed
Copper with Oxygen
Observation
Black copper oxide forms on heating copper.
Aluminium with Oxygen
Nature of Metal Oxides
Most metal oxides are basic in nature.
Example:
Copper oxide reacts with hydrochloric acid to form salt and water.
Amphoteric Oxides
Some metal oxides react with both acids and bases. These are
called amphoteric oxides.
Examples
- Aluminium
oxide
- Zinc
oxide
Aluminium Oxide with Acid
Aluminium Oxide with Base
Metal Oxides Dissolving in Water
Sodium Oxide
Potassium Oxide
Reactivity Towards Oxygen
|
Highly Reactive |
Less Reactive |
|
Potassium |
Copper |
|
Sodium |
Silver |
|
Calcium |
Gold |
- Potassium
and sodium react vigorously and catch fire easily.
- Gold
and silver do not react with oxygen easily.
Anodising
Anodising is the process of forming a thick protective oxide
layer on aluminium.
Advantages
- Prevents
corrosion
- Gives
attractive finish
2. Reaction of Metals with Water
Metals react with water to form:
- Metal
oxide or hydroxide
- Hydrogen
gas
General Reactions
Potassium with Water
Very violent and exothermic reaction.
Sodium with Water
Hydrogen catches fire due to heat produced.
Calcium with Water
Calcium floats because hydrogen bubbles stick to its
surface.
Magnesium with Hot Water
Aluminium with Steam
Iron with Steam
Metals Not Reacting with Water
- Lead
- Copper
- Silver
- Gold
3. Reaction of Metals with Acids
Metals react with dilute acids to form:
- Salt
- Hydrogen
gas
General Reaction
Magnesium with HCl
Aluminium with HCl
Zinc with HCl
Iron with HCl
Copper and Dilute HCl
Copper does not react with dilute hydrochloric acid.
Nitric Acid Exception
Nitric acid usually does not produce hydrogen gas because it
is a strong oxidising agent.
However:
- Magnesium
- Manganese
react with very dilute nitric acid to produce hydrogen gas.
Aqua Regia
A freshly prepared mixture of:
- Concentrated
HCl
- Concentrated
HNO₃
in the ratio 3:1.
Special Property
It can dissolve gold and platinum.
4. Reaction of Metals with Salt Solutions
A more reactive metal displaces a less reactive metal from
its salt solution.
General Reaction
Iron and Copper Sulphate
Observation
- Blue
colour fades
- Brown
copper deposits form
Reactivity Series
The arrangement of metals in decreasing order of reactivity
is called the reactivity series.
|
Most Reactive |
Least Reactive |
|
K |
Au |
|
Na |
Ag |
|
Ca |
Hg |
|
Mg |
Cu |
|
Al |
Pb |
|
Zn |
Fe |
Hydrogen is placed between lead and copper.
HOW METALS AND NON-METALS REACT
Metals lose electrons and form positive ions.
Non-metals gain electrons and form negative ions.
Formation of Sodium Chloride
Sodium loses one electron
Chlorine gains one electron
Ionic Bond
The electrostatic force between oppositely charged ions is
called an ionic bond.
Formation of Magnesium Chloride
IONIC COMPOUNDS
Compounds formed by transfer of electrons are called ionic
compounds.
Examples
- NaCl
- MgCl₂
- CaCl₂
Properties of Ionic Compounds
1. Physical Nature
- Hard
solids
- Brittle
2. High Melting and Boiling Points
Strong electrostatic force requires large energy to break
ionic bonds.
3. Solubility
- Soluble
in water
- Insoluble
in kerosene and petrol
4. Conductivity
|
State |
Conductivity |
|
Solid |
Does not conduct |
|
Molten |
Conducts |
|
Aqueous solution |
Conducts |
OCCURRENCE OF METALS
Minerals
Naturally occurring substances containing metals or their
compounds are called minerals.
Ores
Minerals from which metals can be extracted profitably are
called ores.
Gangue
Impurities like sand and soil mixed with ores are called
gangue.
METALLURGY
The process of extracting metals from ores and refining them
is called metallurgy.
EXTRACTION OF METALS
1. Metals Low in Reactivity Series
Examples:
- Gold
- Silver
- Mercury
These can be obtained by heating their oxides.
Mercury Extraction
Copper Extraction
2. Metals in Middle of Reactivity Series
Examples:
- Zinc
- Iron
- Lead
These are usually extracted using carbon.
Roasting
Heating sulphide ores in excess air.
Zinc Sulphide
Calcination
Heating carbonate ores in limited air.
Zinc Carbonate
Reduction of Zinc Oxide
Thermit Reaction
Highly exothermic reaction used for welding railway tracks.
3. Metals High in Reactivity Series
Examples:
- Sodium
- Potassium
- Calcium
- Aluminium
These are extracted using electrolysis.
Electrolysis of Sodium Chloride
Cathode Reaction
Anode Reaction
REFINING OF METALS
The purification of impure metals is called refining.
Electrolytic Refining
Used for:
- Copper
- Zinc
- Silver
- Gold
Setup
- Impure
metal → anode
- Pure
metal → cathode
- Metal
salt solution → electrolyte
Pure metal gets deposited on cathode.
CORROSION
The gradual destruction of metals by air, moisture or
chemicals is called corrosion.
Examples of Corrosion
Rusting of Iron
Iron reacts with oxygen and moisture forming rust.
Silver
Silver becomes black due to silver sulphide formation.
Copper
Copper develops green coating of basic copper carbonate.
Conditions Necessary for Rusting
Iron rusts only when:
- Air
is present
- Water
is present
If either is absent, rusting does not occur.
PREVENTION OF CORROSION
- Painting
- Oiling
- Greasing
- Galvanisation
- Chrome
plating
- Alloying
Galvanisation
Coating iron with zinc to prevent rusting.
Alloys
Homogeneous mixture of:
- Two
or more metals
OR - Metal
and non-metal
Examples of Alloys
|
Alloy |
Composition |
|
Brass |
Copper + Zinc |
|
Bronze |
Copper + Tin |
|
Solder |
Lead + Tin |
|
Stainless Steel |
Iron + Nickel + Chromium |
Properties of Alloys
- Harder
than pure metals
- More
resistant to corrosion
- Lower
melting points in some cases
24 Carat and 22 Carat Gold
- 24
carat gold → pure gold
- 22
carat gold → gold mixed with copper or silver
Pure gold is soft, so jewellery is made from alloys.
Iron Pillar of Delhi
The Iron Pillar near Qutub Minar has not rusted for more
than 1600 years due to advanced ancient Indian metallurgy techniques.
