Page 64 - NCERT Science Class 10 English Medium

saw how the nature of bonding in ionic compounds explains these
properties. Let us now study the properties of some carbon compounds.
Most carbon compounds are poor conductors of electricity as we
have seen in Chapter 2. From the data
given in Table 4.1 on the boiling and Table 4.1 Melting points and boiling points of some
melting points of the carbon compounds, compounds of carbon
we find that these compounds have low
Compound Melting Boiling
melting and boiling points as compared
point (K) point (K)
to ionic compounds (Chapter 3). We can
conclude that the forces of attraction Acetic acid (CH COOH) 290 391
3
between the molecules are not very
Chloroform (CHCl ) 209 334
strong. Since these compounds are 3
largely non-conductors of electricity, we Ethanol (CH CH OH) 156 351
3
2
can conclude that the bonding in these
Methane (CH ) 90 111
compounds does not give rise to any ions. 4
In Class IX, we learnt about the
combining capacity of various elements and how it depends on the
number of valence electrons. Let us now look at the electronic
configuration of carbon. The atomic number of carbon is 6. What would
be the distribution of electrons in various shells of carbon? How many
valence electrons will carbon have?
We know that the reactivity of elements is explained as their tendency
to attain a completely filled outer shell, that is, attain noble gas
configuration. Elements forming ionic compounds achieve this by either
gaining or losing electrons from the outermost shell. In the case of carbon,
it has four electrons in its outermost shell and needs to gain or lose four
electrons to attain noble gas configuration. If it were to gain or lose
electrons –
(i) It could gain four electrons forming C anion. But it would be difficult
4–
for the nucleus with six protons to hold on to ten electrons, that is,
four extra electrons.
4+
(ii) It could lose four electrons forming C cation. But it would require
a large amount of energy to remove four electrons leaving behind a
carbon cation with six protons in its nucleus holding on to just two
electrons.

Carbon overcomes this problem by sharing its valence electrons with
other atoms of carbon or with atoms of other elements. Not just carbon,
but many other elements form molecules by sharing electrons in this
manner. The shared electrons ‘belong’ to the outermost shells of both
the atoms and lead to both atoms attaining the noble gas configuration.
Before going on to compounds of carbon, let us look at some simple
molecules formed by the sharing of valence electrons.
The simplest molecule formed in this manner is that of hydrogen.
As you have learnt earlier, the atomic number of hydrogen is 1. Hence
hydrogen has one electron in its K shell and it requires one more electron
to fill the K shell. So two hydrogen atoms share their electrons to form a
molecule of hydrogen, H . This allows each hydrogen atom to attain the
2

Carbon and its Compounds 59

2024-25