E-CONTENT PREPARATION FOR CLASS VIII SCIENCE� �CHAPTER-4�Materials : �Metals and Non-Metals

S. Thirumala Reddy TGT Science

Jawahar Navodaya Vidyalaya,

Lepakshi, ANANTAPUR (Dist.)

Andhra Pradesh

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NAVODAYA VIDYALAYA SAMITI, NOIDA

Objectives

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• explain the terms like malleability, ductility and

sonorous.

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• write word equation for reaction of metals with air

and water.

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• differentiate between physical and chemical
• properties of metals and non-metals.

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• list the uses of metals and non-metals.

CONTENTS

• Introduction - Elements and atoms
• Metals , Non-metals and Metalloids
• Physical properties of metals and non-metals
• Chemical properties of metals and non-metals
• Reactivity series of metals
• Displacement reaction
• Uses of metals and non-metals.

Element

• A substance which can not be broken down into two or more simpler substances by chemical reactions ( by applying heat, light or electricity) is called an element.

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SOME COMMON ELEMENTS

Hydrogen, Helium, Carbon, Nitrogen, Oxygen, Sodium, Magnesium, Aluminium, Silicon, Phosphorus, Sulphur, Chlorine, Potassium, Calcium, Iron, Copper, Zinc, Bromine, Iodine, Silver, Gold, Mercury etc.

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• Every element is represented by a ‘symbol’. All the elements have separate symbols. No two elements can have the same symbol.

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• For example, the symbol of Hydrogen is H whereas the symbol of Nitrogen is N.

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• The symbol of an element also represents ‘one atom’ of that element.

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Atom

• The smallest particle of an element is called ‘atom’.
• An element is a substance which is made up of only one kind of atoms.
• For example, Oxygen element is made up of only oxygen atoms whereas iron element is made up of iron atoms.

• The atoms of an element remain unaffected by the physical changes in the element.

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For example, atoms of liquid sulphur or vapour

forms of sulphur would be the same as that of solid

sulphur.

• Although there is a great variety of substances in the universe but the number of elements forming these substances is limited.

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• There are only 94 naturally occurring elements.

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• An important classification of elements is in terms of metals, non-metals and metalloids.

�Physical properties of Metals and Non-metals

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• 1. Malleability

The property with which metals can be beaten

into thin sheets is called malleability.

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Most of the metals are malleable.

Gold and Silver are the best malleable metals.

Aluminium and Copper are also highly malleable metals.

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• Ironsmith can change the shape of a block of iron metal by hammering to make different iron objects such as an axe, a spade or a shovel, etc.

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• Non-metals are not malleable. They are brittle.

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They break into small pieces when hammered.

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• Carbon is a non-metal. Carbon is found in many forms such as charcoal, coke, graphite ,etc. Coal is also mainly carbon.

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• Pencil lead is a form of carbon called graphite. If we take a pencil lead and beat it with a hammer, it will break into pieces.

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�Ductility

• Most of the metals are ductile.

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• The property by which metals can be drawn into wires is called ductility.

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• Gold and Silver are the best ductile metals.

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Copper and aluminium metals are also very ductile and can be drawn into thin copper wires and aluminium wires ( which are used as electric wires).

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• Non –metals are not ductile. They cannot be drawn into wires.

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Sonorous

• Metals are sonorous. This means that metals make ringing sound when we strike them.

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• When the hammer of an electric bell strikes the metal gong, a ringing sound is produced.

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• Non-metals are not sonorous.

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• For example, if we drop a piece of carbon ( Charcoal) or a lump of sulphur on the floor or strike them with a hammer , we do not hear any ringing sound.

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Conductivity

• Metals are good conductors of heat and electricity. They allow heat and electricity to pass through them easily.
• For example, copper, silver, gold, aluminium and iron are good conductors of heat.
• Silver metal is the best conductor of heat. Copper metal is a better conductor of heat than aluminium metal.

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• Electric wires are made of metals because they allow electricity to pass through them easily.
• Copper wires are used in house hold electric wiring since it is a better conductor of electricity than aluminium.
• Silver metal is the best conductor of electricity.

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• Non-metals are poor conductors of heat and electricity.

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• For example, phosphorous and sulphur are non-metals. They do not conduct heat and electricity.

• Many of the non-metals are, infact, very good insulators.

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• There are, however, some exceptions. A form of carbon element, graphite is a non-metal which is a good conductor of electricity.

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Lustre

• Metals are lustrous. They have a shiny appearance.

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• If we observe the freshly cut surface of metals, we will find that they have a shiny appearance. This is called metallic lustre.

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• For example, gold and silver are used for making jewellery because they are bright and shiny.

• Non-metals are not lustrous. They are dull in appearance.

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• However, there is one exception. Iodine is a non-metal having lustre.

Hardness

• Metals are generally hard. They cannot be cut easily.
• Sodium and Potassium are soft metals. They can be cut with a knife easily.

• Most of the solid non-metals are quite soft. They can be cut easily.

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• Diamond, a form of solid non-metal, carbon, is very hard. Infact, diamond is the hardest natural substance known.

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• Mercury is a metal. It exists in liquid state at room temperature.
• Mercury is used in making thermometers.

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• Bromine is a non-metal. It exists in liquid state at room temperature.

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Chemical properties of metals and non-metals

• Reaction with oxygen:

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Metals react with oxygen to form metal oxides. Metal oxides are basic in nature.

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Metal + Oxygen 🡪 Metal oxide

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When magnesium burns in air, it combines with oxygen of air to form magnesium oxide ( basic oxide).

Magnesium + Oxygen 🡪 Magnesium oxide

• Magnesium oxide dissolves in water to form magnesium hydroxide solution.

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Reaction of iron metal with oxygen of air in nature

Iron metal combines slowly with the oxygen of air in the presence of water ( moisture) to form a compound called ‘iron oxide’. This iron oxide is called rust.

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4 Fe + 2H2O + 3O2 🡪 2Fe2O3.H2O

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Reaction of copper metal with moist air in nature

• If copper object is exposed to moist air for a long time, then copper reacts with water, carbon dioxide and oxygen present in the moist air to form a green coating on the copper object.

The green coating is a mixture of copper hydroxide and copper carbonate.

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• Sodium and Potassium are highly reactive metals with oxygen and water.

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In order to prevent their reaction with atmospheric oxygen and water, they are always stored under kerosene.

Reaction of a non-metal with oxygen

• Non-metals react with oxygen to form non-metal oxides. Non-metal oxides are acidic in nature.

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• The acidic non metal oxides turn blue litmus to red.

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• Non-metal + Oxygen 🡪 Non-metal oxide

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• When sulphur burns in air, it combines with oxygen of air to form sulphur dioxide (acidic oxide).

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Sulphur + Oxygen 🡪 Sulphur dioxide

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Sulphur dioxide dissolves in water to form sulphurous acid solution.

Sulphur dioxide + water 🡪 Sulphurous acid

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Sulphurous acid turns blue litmus to red showing that it is an acid.

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Reaction with water

• When a metal reacts with water, then a metal hydroxide and hydrogen gas are formed.

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Metal + Water 🡪Metal hydroxide + Hydrogen

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• Some metals react vigorously even with cold water.

Ex. Sodium

• Some metals react with hot water. Ex. Magnesium
• Some metals react with steam. Ex. Zinc and Iron
• Some metals don’t react with water and steam.

Ex. Copper, Silver, Gold

• Non-metals do not react with water.

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Phosphorous is a very reactive non-metal. If phosphorous is kept open in air, it reacts with the oxygen of air and catches fire. So, in order to protect phosphorous from atmospheric air, it is stored in water.

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Reaction with acids

• Most of the metals react with dilute acids to form salt and hydrogen gas.

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Metal + Acid 🡪 Salt + Hydrogen

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Ex. Zinc + Hydrochloric acid --🡪 Zinc chloride + Hydrogen

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Hydrogen gas puts off a lighted match stick with a ‘pop’ sound when it is brought near the mouth of a test- tube containing a metal and dilute acid.

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The less reactive metals like copper, silver and gold do not react with dilute acids

• Copper metal does not react with dilute sulphuric acid to produce hydrogen gas. However, it reacts with hot and concentrated sulphuric acid but no hydrogen gas is produced.

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• Non-metals do not react with dilute acids to form salts and hydrogen gas.

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• Certain food stuffs like citrus fruit juices ( orange juice), pickles, chutney and curd, etc., contain acids. When they are kept in iron, aluminium or copper containers, the acids present in them react with the metal of container slowly to form toxic salts. These toxic salts can make us sick and damage our health.

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Reaction with bases

All metals do not react with bases like sodium hydroxide. Some metals react with bases to form salts and hydrogen gas.

Metal + Base 🡪 Salt + Hydrogen

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• Aluminium is a metal. Sodium hydroxide is a base. When aluminium is heated with sodium hydroxide solution, Sodium aluminate (salt) and hydrogen gas are formed.

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• Aluminium+ Sodium hydroxide 🡪 Sodium aluminate + Hydrogen

• Zinc metal also reacts with sodium hydroxide solution to form salt and hydrogen gas.

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Zinc + Sodium hydroxide 🡪 Sodium zincate + Hydrogen

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The reactions of non-metals with bases are complex.

Reactivity series of metals

• Some metals are very reactive whereas other metals are less reactive or unreactive.

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• Reactivity series of metals is the descending order of metals with their reactivities.

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• In the reactivity series, the most reactive metal is placed at the top and the least reactive metal is placed at the bottom

Displacement reaction

A chemical reaction in which a more reactive metal displaces a less reactive metal from its salt solution is called displacement reaction.

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Ex. 1 Adding iron nails to

copper sulphate solution.

Iron is a more reactive metal than copper. So, iron displaces copper from its salt solution i.e copper sulphtate solution(blue) and forms green coloured iron sulphate. The free copper is seen as brown coat on iron nails.

• Ex.2

If we add few copper metal strips to iron sulphate solution, no displacement reaction takes place because copper is a less reactive metal than iron. So, copper can not displace iron from it’s salt solution (iron sulphate solution).

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Copper + Iron sulphate 🡪 No displacement reaction

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Ex.3

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If we add one or two zinc metal granules to Copper sulphate solution, the blue colour gradually disappears and solution becomes colourless due to the formation of zinc sulphate solution. The brown copper is deposited on zinc granules.

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Zinc + copper sulphate 🡪 Zinc sulphate + copper

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Zinc is a more reactive metal than copper.

Ex.4

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If we place a strip of copper metal in zinc sulphate solution, then no displacement reaction will take place.

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Copper + Zinc sulphate 🡪 No displacement reaction

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Ex 5.

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When a zinc metal granule is added to iron sulphate solution, then displacement reaction will take place to form zinc sulphate and iron.

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Zinc + Iron sulphate 🡪 Zinc sulphate + iron

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Ex.6

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If we place an iron nail in zinc sulphate solution, then no displacement reaction will take place because iron is less reactive than zinc.

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Iron + Zinc sulphate 🡪 No displacement reaction

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Uses of metals

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• Metals like iron, copper and aluminium are used to make cooking utensils and water boilers.

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• Copper metal is used in making electrical wires and electric appliances.

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• Aluminium metal is used for making electric cables. It is also used to make aeroplanes.

• Iron metal is used to make nails, screws, machines, railway lines, vehicles such as buses, cars and agricultural tools like plough, hoe etc.

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• Zinc metal is used for galvanizing iron to prevent rusting.

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• Some metals like gold and silver are used in making jewellery.

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• Mercury metal is used in making thermometers.

Uses of non-metals

• Oxygen is a non-metal . It is used by all living organisms for breathing.

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• Nitrogen is a non-metal. It is used in making fertilisers to improve the growth of plants.

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• Chorine is non-metal. It is used to kill the germs present in water.

• Iodine is a none-metal. It is used to make a purple coloured solution called Tincture iodine. It is applied on wounds as an antiseptic.

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• Sulphur and Phosphorus are used fireworks(crackers).

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• Carbon is a non-metal. It is used in the form of graphite, to make pencil leads and electrodes

Metalloids

• The elements whose properties are intermediate between those of metals and non-metals are called metalloids.

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• Ex. Silicon, Germanium, Arsenic etc.

THANK YOU