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Chemistryfor students of class X

Score n learn

CONTENTS

Chemical Reactions and Equations 7Chapter 1

Acids, Bases and Salts 33Chapter 2

Metals and Non-Metals 61Chapter 3

Carbon and its Compounds 99Chapter 4

Periodic Classification of Elements 129Chapter 5

The following 3 pages will give you a

glimpse of how effectively we have used

illustrations along with simple language

to explain a concept. The following pages

are from the part of the chemistry book

for X grade, these pages detail -

“Can you explain why elements cannot be

classified as metals and non-metals only

on the basis of their physical properties?”

66

Can you explain why elements cannot be classified as metals and non-metals only on the basis of their physical properties? This is because there are many exceptions in terms of physical properties of metals and non-metals. Some of the exceptions are given below:

Exceptions in metals:• All the metals exist in solid state, except mercury that exists in liquid

state.• Metals have high melting and boiling points, but metals like gallium

and caesium have very low melting points. The melting points of these metals are so low that they melt when held in the hand. The melting points of sodium and potassium are also very low.

• Metals are very hard, but some metals such as lithium, sodium and potassium are very soft and can be cut with a knife.

Exceptions in non-metals:• All the non-metals are soft, but diamond (an allotrope of carbon) is the

hardest known naturally occurring substance.• Non-metals are poor conductors of electricity, but graphite (an allotrope

of carbon) is a good conductor of electricity.• The lustre associated with non-metals is dull, but iodine has lustre like

metals. Diamond is one of most lustrous substances.• Solid non-metals have low melting and boiling points, but the melting

and boiling points of diamond are very high.

Hence, we cannot consider an element as a metal or a non-metal only on the basis of its physical properties. Elements can be classified as metals and non-metals more easily by observing their chemical properties.

Let us perform following experiment to distinguish metal and non-metals on the basis of their chemical properties.

Take a magnesium ribbon and 2 g sulphur powder. First, burn the magnesium ribbon and collect the ashes (shown in figure 3 (a)). Dissolve the ashes in water and test the resulting solution with both red and blue litmus paper (shown in figure 3 (b)). After this, burn sulphur and collect the fumes in a test tube (shown in figure 4 (a)). Add some water to the test tube. Test the resulting solution with both blue and red litmus paper (shown in figure 4 (b)).

Observations:You will find that the red litmus paper turns blue with the resulting solution obtained by dissolving ashes while the blue litmus paper remains blue. You will also find that the blue litmus paper turns red with the resulting solution obtained by dissolving SO2 fumes while the red litmus paper remains unaffected in this solution.

In the Laboratory

3

Know more

Fluorine is the most reactive non metal. It reacts with almost all other elements.

Result: Magnesium, when heated, burns with a white dazzling flame to form magnesium oxide.

( ) ( ) ( )2

Magnesium Oxygen Magnesium oxide

2 Mg s O g 2MgO s+ →

Magnesium oxide dissolves in water to form magnesium hydroxide.

( ) ( ) ( ) ( )2 2

Magnesium oxide Water Magnesium hydroxide

MgO s H O s 2Mg OH s+ →

Magnesium hydroxide is basic in nature and hence, turns red litmus paper blue. Blue litmus paper remains unaffected in this solution.

Sulphur, when heated, burns to produce the fumes of sulphur dioxide (SO2).

( ) ( ) ( )2 2

Sulphur Oxygen Sulphur dioxide

S s O g SO s+ →

Figure 3(a): Burning of magnesium ribbon Figure 3(b): Dissolved ashes in water

Figure 4(a): Burning of sulphur powder Figure 4(b): Dissolved fumes in water

68

Sulphur dioxide dissolves in water to form sulphurous acid. It is an acid and hence, turns blue litmus paper red. The red litmus paper remains unaffected in this solution.

( ) ( )2 2 2 3

Sulphur dioxide Water Sulphurous Acid

SO g H O s H SO+ →

Conclusion:Hence, from this experiment, we can conclude that metals give basic oxides. When these oxides are dissolved in water, the resulting solutions are basic in nature. It can also be concluded that most non-metals give acidic oxides. When these oxides are dissolved in water, the resulting solutions are acidic in nature.

Now, let us study the chemical properties of metals.

CHEMICAL PROPERTIES

Metals1. Reaction of metals with air: Metals burn when they react with oxygen present in air to form oxides. Almost all metals react with oxygen to form basic oxides. The general reaction for this process is:

Metal Oxygen Metal oxide + → The reactivity of metals with oxygen varies. Some metals such as sodium react with oxygen at room temperature. Metals such as magnesium do not react with oxygen at room temperature and require heating. When magnesium is heated, it burns with a dazzling white flame to form magnesium oxide. Metals such as zinc do not react with oxygen easily and require very strong heating.

Reactivity of metals with oxygen to form metal oxides:

• Sodium and potassium react with oxygen very vigorously at room temperature to form sodium oxide and potassium oxide respectively. The given equation shows the reaction:

( ) ( ) ( )2 2

Sodium Oxygen Sodium oxide

4 Na s O g 2 Na O s

+ →

( ) ( ) ( )2 2

Potassium oxygen Potassium oxide

4K s O g 2K O s+ →

Both sodium and potassium react very vigorously with oxygen. Hence, they catch fire if kept in the open. Lithium also reacts with oxygen in the similar manner to form lithium oxide. Hence, all these elements are

Know more

Silver is used for making mirrors because of its excellent shine and reflective nature.

This book contains expected learning objectives from a

chapter, simple content supported with lot of illustrations and

sectional assessments and comprehensive exercises at

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