Page 54 - NCERT Science Class 10 English Medium

You may have observed the following general properties for ionic
compounds—
(i) Physical nature: Ionic compounds are solids and are somewhat
hard because of the strong force of attraction between the positive
and negative ions. These compounds are generally brittle and
break into pieces when pressure is applied.
(ii) Melting and Boiling points: Ionic compounds have high melting
and boiling points (see Table 3.4). This is because a considerable
amount of energy is required to break the strong inter-ionic
attraction.
(iii) Solubility: Electrovalent compounds are generally soluble in
water and insoluble in solvents such as kerosene, petrol, etc.
(iv) Conduction of Electricity: The conduction of electricity through
a solution involves the movement of charged particles. A solution
of an ionic compound in water contains ions, which move to the
opposite electrodes when electricity is passed through the
solution. Ionic compounds in the solid state do not conduct
electricity because movement of ions in the solid is not possible
due to their rigid structure. But ionic compounds conduct
electricity in the molten state. This is possible in the molten state
since the elecrostatic forces of attraction between the oppositely
charged ions are overcome due to the heat. Thus, the ions move
freely and conduct electricity.

Q U E S T I O N S

1. (i) Write the electron-dot structures for sodium, oxygen and
magnesium.
(ii) Show the formation of Na O and MgO by the transfer of electrons. ?
2
(iii) What are the ions present in these compounds?
2. Why do ionic compounds have high melting points?

ALS
3 3 3 3 . 4 OCCURRENCE OF METOCCURRENCE OF METALS
OCCURRENCE OF METALSALS
3.4 .4.4 .4 OCCURRENCE OF METOCCURRENCE OF METALS
The earth’s crust is the major source of metals. Seawater also contains
some soluble salts such as sodium chloride, magnesium chloride, etc.
The elements or compounds, which occur naturally in the earth’s crust,
are known as minerals. At some places, minerals contain a very high
percentage of a particular metal and the metal can be profitably extracted
from it. These minerals are called ores.

3.4.1 Extraction of Metals

You have learnt about the reactivity series of metals. Having this
knowledge, you can easily understand how a metal is extracted from its
ore. Some metals are found in the earth’s crust in the free state. Some
are found in the form of their compounds. The metals at the bottom of
the activity series are the least reactive. They are often found in a free

Metals and Non-metals 49

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