CBSE Class 8 Science _Metals and non metals

4/7/2021 ACE Learning Hub Mob:93600 48588 1

There are variety of substances found in nature. These can be categorized into two
parts:
1. Natural substances
2. Artificial or man-made substances
Natural substances: These are those substances which are found naturally.
For example: coal and petroleum.
Natural substances are further divided into two types:
1. Metals
2. Non-metals

Artificial substances:
These are those substances which are not found in nature or are made artificially
by man.
For example: chair, table, tube light etc.
Matter: Anything that occupies space and has mass (quantity of matter, For
example: Pen and ball) is called matter.
John Dalton: He gave Dalton’s theory in which he clearly stated that matter is
made of small particles called atoms.
Neil Bohr Theory: An atom is spherical in nature and has a nucleus placed at
the center of the atom. Atoms are electrically neutral.
He stated that an atom has three fundamental particles as follows-
Electrons, Protons, Neutrons

• Electrons are positively charged.
• Protons are negatively charged.
• Neutrons are not charged.
In an atom, there is only one nucleus which is placed at the center.
Valence orbit/shell: The outermost shell of an atom is known as valence shell.
Valence electrons: The electrons which are present in the outermost shell.
Valency: Valency is used when one atom combines with another atom. Valency
totally depends upon the valence electrons.

Introduction to Metals
What are Metals?
Those materials which possess the characteristic of being hard, shiny, malleable,
fusible, ductile, etc. are termed as metals. Few examples of metals are iron, gold,
silver, aluminium, copper, etc.
Physical Properties of Metals
These are the properties which we come to know by just touching, seeing, color,
etc.
1. Malleable:
It is that property of metals which allows them to be beaten into
the thin sheets. Due to presence of this property, the shape of
iron nail and aluminium wire can be changed on beating.

For example:
The silver foils used for decorating sweets and the aluminium foil
used for wrapping food.
Malleable metals are aluminium and copper.
Highly malleable metals are gold and silver.

2. Conductivity:
It is that property of metals which allows the current and heat to pass through
them easily.
For Example- Metals like iron rod, nail, copper wire, etc. are good conductors
of electricity

3. Ductility: It is that property of metals which allows them to be drawn into the
wires.
For example: Metals like aluminium and copper are used to make wires which
are used in electric connection as they are ductile metals.
Zinc, Arsenic, and antimony are non-ductile metals.

4. Sonorous: It is that property of metals which produces ringing sounds on
hitting.
Ringing property of metal depends on the temperature and density.
Q. Why are bells made of metals?
Answer: Metals have sonorous property. Ringing sound produced by metals is
known as sonority. So, bells are made of metals.
5. Lustrous: It is that property of metals which makes them shine and their
structures are capable of reflecting incident light.
For example: Gold, silver, copper, and platinum.
Metals like sodium and potassium are soft and can be cut with a knife.
6. Hardness: Due to the ductility and malleability properties, metals are very
strong and some of the metals which have the properties of non ductile and non
malleable are not all strong.

7. Solid at room temperature: Most of the metals are solid (particles are tightly
and very closely packed) at room temperature.
There are a few exceptions.
Mercury and Gallium are the metals which are found in liquid state at room
temperature.
8. High Melting and boiling point: Most of the metals have high melting and boiling
points. The metals which are solid in nature always have high melting and boiling
points because they are closely packed and have high attraction.
There are few exceptions.
Sodium, potassium, Mercury, and Gallium have low melting and boiling points.
9. High tensile strength: The metals which can bear the strain are termed as the
high tensile strength metals.
Here are few exceptions
Zinc, Arsenic, and Antimony have low tensile strength.

• Some materials are hard, lustrous, malleable, ductile, sonorous and good
conductors of heat and electricity.
• The materials which generally possess these properties are called metals.
• The examples of metals are iron, copper, aluminium, calcium, magnesium,
etc.
• In contrast, materials like coal and sulphur are soft and dull in appearance.
• They break down into a powdery mass on tapping with a hammer.
• They are not sonorous and are poor conductors of heat and electricity.
• These materials are called non-metals.
• The examples of non-metals are sulphur, carbon, oxygen, phosphorus, etc.

Chemical Properties of Metals
1. Reaction of Metals with Oxygen: Generally, when metals are reacted with
oxygen, they will form metallic oxides. These metallic oxides are basic in nature.
Example 1: Rusting of Iron. Following is the reaction to express it.
Iron (Fe) + Oxygen (O2) + Water (H2O) → Iron Oxide (Fe2O3)
Example 2:
2Cu + H2O + CO2 + O2→ Cu (OH)2 (copper hydroxide) + CuCO3 (copper
carbonate)
Testing of nature of Rusting-
Follow the given steps-
(i) Collect a spoonful of rust and dissolve it in a very little amount of water.
(ii) The rust remains suspended in water. Shake the suspension well.
(iii) Test the solution with red and blue litmus papers. The red litmus turns blue.
So, we imply that, generally, metallic oxides are basic in nature.

2. Reaction of Metals with Water:
Some metals react vigorously with water like in case of sodium. It is stored in
kerosene oil.
Some metals react with water to form metal oxides and metal hydroxides.
Hydrogen gas is released in this reaction.
On the other hand, some metals react very slowly with water like in case of iron
For example:
Na + H2O → NaOH + H2
Sodium + water → Sodium hydroxide
Ca + H2O → Ca(OH)2 + H2
Calcium + Water → Calcium hydroxide

Some metals react with cold water, some with hot water, and some metals react
with steam.
Metals which react with cold water are more stable as their hydroxides are stable.
For example: Potassium, Sodium, and Calcium.
K + H2O → KOH + H2
Na + H2O → NaOH + H2
Some metals react with hot water and form oxides.
For example: Magnesium.
Mg + H20 → MgO + H2
Magnesium Water Magnesium oxide
Some metals react with steam.
For example: Aluminium, Iron, and Zinc.
Fe + H2O → Al2O3 + H2
Iron (Steam)
Zn + H2O → ZnO + H2
Al + H2O → Al2O3 + H2
Cu + H2O → No reaction

3. Reaction of Metals with Dilute Acids:
Generally, a metal reacts with acids and releases hydrogen gas with a ‘pop’ sound.
The presence of hydrogen gas is confirmed by bringing a burning matchstick or
candle near the gas. And when the burning matchstick or candle produces pop
sound then it means that hydrogen gas has evolved.
For example:
Na + HCl → NaCl (Sodium chloride) + H2
Mg + H2SO4 → MgSO4 ( Magnesium Sulphate) + H2
Ca + HNO3 → Ca(NO3)2 ( Calcium nitrate) + H2
It is found that, copper does not react with hydrochloric acid while it reacts with
sulphuric acid.
Cu (less reactive) + HCL (more reactive) → No reaction
Cu + HOH → No reaction

4. Reaction of metals with metals salt solution:
When salt of metal B reacts with metal A:
Salt of metal B + Metal A → Salt of metal A + Metal
For example:
CuSO4(Blue color) + Zn (more reactive) → ZnSO4( colorless) + Cu
The five important uses of metals are as follows –
(i) Lead is used in X-ray machines.
(ii) Iron is used in construction.
(iii) Mercury is used in thermometers.
(iv) Gold and silver are used in making jewellery.
(v) Aluminium foil is used for packing food.

Introduction to Non-Metals
What are Non-Metals
Those materials which do not possess the
characteristics of metals are termed as
non-metal.
• Materials like coal and sulphur are soft
and dull in appearance.
• They break down into powdery mass on
tapping with hammer.
• They are non-sonorous and are
• poor conductors of heat and electricity.
Few examples of non metals are sulphur,
carbon, oxygen etc.

1. Non-Malleable: Non-metals are generally brittle and hence cannot be beaten into
sheets or drawn into wires. In other words, non-metals are non-malleable and
non-ductile. Where stress is applied on non-metals, they shatter into pieces.
For example: Sulphur and phosphorous. These non-metals are in the form of
powder and cannot be beaten.
2. Non-Ductile:
Non metals are non-ductile because they cannot be melted and drawn into thin
wires. They are brittle in nature.
3.Poor conductors of heat and electricity: Non-metals are generally bad conductors
of heat and electricity as they do not have free electrons.
Carbon (graphite) is an exception. Graphite is an allotrope of carbon as it is a good
conductor of electricity due to its special crystalline arrangement. It is used in making
electrodes.

4.Non-sonorous: Non-metals which do not make any sound when hit with an
object are known as non-sonorous. For example: Phosphorous.
5.Non-Lustrous: These are the non-metals which are in the form of powder and
gas. Hence, they cannot be polished and do not have any lusture.
Non-metals are generally non-lustrous and dull. Carbon (graphite) and iodine
are exceptions. They are lustrous, as their surface possesses a shine.
6. Softness: Non-metals are generally soft. Due to non-ductile and non-
malleability properties, non metals are not strong at all.
However, carbon (diamond) is an exception. Diamond is very hard. In fact,
diamond is the hardest natural substance known.

Solid, Liquid or Gas at room temperature: Non-metals may exist in solid,
liquid or gaseous state at room temperature.
For example, carbon, sulphur and phosphorus are solid at room
temperature. Nitrogen and oxygen are gaseous non-metals. Bromine is a
non-metal which is liquid at room temperature.
Low Melting and boiling point:
Non-metals are loosely packed and therefore, less heat is required to melt
or boil them. Hence, non-metals possess low melting and boiling points,
except graphite.
Carbon (graphite) is a non-metal but possesses high melting point.
Low Tensile Strength: Non-metals cannot bear the strain. Thus, they have
low tensile strength. They are not strong and get easily broken.

4. Reaction with bases: The reaction between non-metals and bases is a very
complex one. Reaction of chlorine with bases like sodium hydroxide gives products
like sodium hypochlorite as well as water.

Q: State whether the following statements are True/False.
1. The property of metals by virtue of which they can be drawn into wires is called
ductility.
2. Metals are good conductors of electricity but poor conductor of heat.
3. Articles made up of metals produce ringing sound when struck hard.
4. Oxides of non-metals and metals are acidic in nature.
5. A less reactive metal displaces a more reactive metal from its salt solution in
water.
1. True
2. False. metals are good conductors of heat and electricity.
3. True because metals are sonorous.
4. False. oxides of non-metals are acidic in nature and oxides
of metals are basic in nature.
5. False, a more reactive metal displaces a less reactive metal
from its salt solution in water.

Corrosion
• Corrosion is an oxidation reaction with atmospheric oxygen in the presence of
water on the surface of a metal.
• During corrosion, metals get converted to oxides, hydroxides, sulphides, etc.
• Generally corrosion occurs when most or all of the atoms on the same metal
surface are oxidized, damaging the entire surface.
• Most metals are easily oxidized and they tend to lose electrons to oxygen in the
air or in water. As oxygen is reduced (gains electrons), it forms an oxide with the
metal.
• Corrosion is a dangerous and extremely costly problem. Because of it, buildings
and bridges can collapse, oil pipelines break, chemical plants leak, and
bathrooms flood.

The corrosion of iron is called rusting.
The Conditions necessary for Rusting are as follows-
Moisture
Air
For example:
Fe + O2 → Fe2O3 (Rust which is brown in color) + H2O

Prevention of Corrosion (Rusting)
The steps involved in the prevention of corrosion are:
• Painting
• Greasing
• Electroplating
• Galvanization
• Alloying
1. Painting: Coating a metal surface with paint or enamel provides a barrier
between the metal and the moisture in the environment.
For example: Railway coaches, automobiles, aircraft.
The process of coating a metal surface with another metal that is more likely to
be oxidized is referred to as sacrificial coating.

2. Greasing: The application of greasing on metal surfaces is helpful in preventing
the contact of the metal surface with air and moisture to prevent its corrosion. For
example: Lubricating bicycle parts with grease to reduce friction and prevent
corrosion.
3. Electroplating: It is the process of coating a thin layer of metal over the other
alignment by hydrolysis. This process not only helps to prevent corrosion, but also
makes the metallic surface shiny.
For example: Iron is electroplated with copper or chromium to prevent rusting. Also,
taps and door knobs are electroplated. Electroplating is widely used in industries
such as automobile, airplanes, electronics, jewelry, and toys.
Electroplating is helpful for manufacturers to utilize inexpensive metals such as steel
or zinc for the majority of the products and then apply different metals on the outside
to account for appearance, protection, and other properties that are desired for the
product. There are also specific types of electroplating such as copper plating, silver
plating, and chromium plating.

4. Galvanization: It is the process of applying a protective thin layer of Zinc to
steel or iron in order to prevent rust and corrosion.
As Zinc prevents iron from corrosion because it does not allow air to pass
through it and form Zinc oxide, Zinc oxide is impermeable in nature.
Zn + O2 → ZnO( Zinc oxide)
Rust is iron oxide (typically a red oxide) which is formed in the presence of
water or air moisture by the reduction and oxidation reaction of iron and
oxygen.

Painting
Grease Greasing
Galvanizing Compound Galvanized Pipes

Difference between chemical properties of metals and non
metals

5. Alloying: An alloy is a metal that is combined with other substances to create a
new metal.
For example: the alloy can be stronger, harder, tougher, or more malleable than
the original metal.
The predominant metal in the alloy is called the base metal.
The other metals or elements added to the alloy are called alloying elements.
Characteristics of alloying:
• It improves the property of substance.
• It makes the metal more durable.
• It makes the metal corrosion resistant.

CBSE Class 8 Science _Metals and non metals

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