In the previous section, we completed the discussion on the compounds of some non-metals. In this section we will discuss about Carbon and it's compounds.
• These chemical compounds are made up of elements.
■ If we make a list of ten things that we use in our day to day life, most of the items in that list will contain carbon.
Food items, clothes, oils, soaps, cosmetics, fuels, paints, rubber, paper etc., are all made up of compounds of carbon. In addition to this, plant and animal bodies are made up of carbon compounds. New compounds of carbon are being discovered or created artificially almost every day.
The atomic number of carbon is 6. It's electronic configuration is 2,4. So it will have 4 valence electrons.
To attain the stable electronic configuration:
• the carbon should lose the 4 electrons.
• or, it should gain 4 new electrons.
Both the above options are difficult. Let us see the reason:
■ A large amount of energy will be required to remove the four valence electrons. Even if they are removed, the 6 protons in the nucleus will be attracting just 2 electrons. This is not possible. So, removal of 4 electrons will not occur
■ If the carbon atom is to gain 4 electrons, the 6 protons in the nucleus will have to attract and hold 10 electrons in the shells. This is difficult. So gaining of electrons also will not occur
What occurs is the sharing of electrons. This will give rise to covalent bonds between carbon atom and atoms of other elements. We have seen the details about covalent bonds earlier. Let us now draw the covalent bonds in some of the carbon compounds:
■ First we will take Methane (CH4)
We have already seen it when we discussed about covalent bond. The details are presented here again.
• Carbon has an atomic number 6. It’s electronic configuration is 2,4. It has 4 electrons in the outer most shell. It needs four more electrons to attain octet.
• Hydrogen has an atomic number 1. It’s electronic configuration is also 1. It has 1 electron in the outer most shell. It needs one more electron to attain octet.
• We see that both carbon and hydrogen are in ‘need for electrons’. They cannot donate any electrons. So the only solution is to form a covalent bond as shown in fig.8.1 below:
• The details about this bond can be written as:
• One carbon atom combines with 4 hydrogen atoms. Each of the four hydrogen atoms share one pair of electrons with the carbon atom
• In total, four pairs (that is., eight electrons) are shared. The eight electrons in the pairs, belongs to both the carbon atom and the hydrogen atom.
• The carbon atom now has the required four electrons for octet.
• The hydrogen atom now has the required 2 electrons for octet
• As the pair belongs to both the atoms, they will not be able to move away from each other
• That is., the carbon and four hydrogen atoms will have to always stick together. Thus a bond is formed between the five atoms
• In each bond, there is a sharing of one pair of electrons. So each bond is a 'single bond'. So methane can be represented as shown in fig.8.2(a) below. The 'single lines' between C and H indicates 'single bonds'.
■ Next we will consider Carbon dioxide (CO2)
• Carbon has an atomic number 6. It’s electronic configuration is 2,4. It has 4 electrons in the outer most shell. It needs four more electrons to attain octet.
• Oxygen has an atomic number 8. It’s electronic configuration is 2,6. It has 6 electrons in the outer most shell. It needs two more electrons to attain octet.
• We see that both carbon and oxygen are in ‘need for electrons’. They cannot donate any electrons. So the only solution is to form a covalent bond as shown in fig.8.3 below:
• The details about this bond can be written as:
• One carbon atom combines with 2 oxygen atoms. Each of the two oxygen atoms share two pairs of electrons with the carbon atom
• In total, four pairs (that is., eight electrons) are shared. The eight electrons in the pairs, belongs to both the carbon atom and the oxygen atoms.
• The carbon atom now has the required 4 electrons for octet.
• The oxygen atoms now has the required 2 electrons for octet
• As the pair belongs to both the atoms, they will not be able to move away from each other
• That is., the carbon and two oxygen atoms will have to always stick together. Thus a bond is formed between the three atoms
• In each bond, there is a sharing of two pairs of electrons. Thus each bond is a 'double bond'. So carbon dioxide can be represented as shown in fig.8.2(b) above. The 'double lines' between C and O indicates 'double bonds'.
How is it possible for the carbon to form such large number of compounds?
Let us analyse the reasons:
Reason 1
We know that carbon has 4 electrons in it's outer most shell. That is., it has a valency of 4. This makes it possible to form 3 different types of bonds. They are shown in fig.8.4 below:
• In the fig., the green dots indicate the electrons already possessed by the carbon atom.
• The red dots indicate the new electrons which are acquired by sharing.
Let us see each type in detail:
1. In fig.8.4(a), the carbon is in bond with 4 other atoms. Each bond is a single bond. Through this arrangement, 4 new electrons are acquired. Thus octet is achieved.
2. In fig.b, the carbon is in bond with 3 other atoms. The bond with one of them is a double bond. Through this arrangement, 4 new electrons are acquired. Thus octet is achieved.
3. In fig.c, the carbon is in bond with 2 other atoms. The bond with one of them is a triple bond. Through this arrangement, 4 new electrons are acquired. Thus octet is achieved.
■ Thus there are three methods by which a carbon atom can enter into bond with others. The bonds so formed are very strong. The reason for the strong bonds can be explained as follows:
• The size of a carbon atom is small. So the force of attraction between the central nucleus and the outer most electrons will be strong. This gives strong bonds. So the molecules thus formed are very stable.
The chemical properties of the newly formed molecules will depend upon the properties of carbon and also the newly bonded elements.
Reason 2
Carbon has the unique ability to enter into bondage with other carbon atoms.
• Because of this ability, long chains of carbon atoms can be formed. This is shown in fig.8.5(a) below:
• From a chain, another chain can branch off as shown in fig.b.
• The end carbon in a chain may enter into bondage with the first carbon to form a ring. This is shown in fig.c.
■The ability of atoms of an element to combine among themselves and form chains is called catenation. Chains, branched chains and rings are formed because of this property.
• Carbon has the ability to catenate.
• But it is not seen in other elements. Silicon some times forms chains up to a maximum of 8 atoms long. But the molecules thus formed are very reactive.
• We have seen that the carbon bond is very strong and hence stable. So a large variety of carbon compounds are possible.
So we have seen two reasons. The formation of very large number of carbon compounds can be explained using those two reasons.
In the next section, we will see the actual arrangement of atoms in a molecule of Carbon compounds.
Importance of Carbon
• We know that all substances around us are made up of chemical compounds.• These chemical compounds are made up of elements.
■ If we make a list of ten things that we use in our day to day life, most of the items in that list will contain carbon.
Food items, clothes, oils, soaps, cosmetics, fuels, paints, rubber, paper etc., are all made up of compounds of carbon. In addition to this, plant and animal bodies are made up of carbon compounds. New compounds of carbon are being discovered or created artificially almost every day.
Bonding between atoms in carbon compounds
We know that, any compound will have atoms of various elements. A carbon compound will have atoms of carbon and one or more other elements. The other elements may be hydrogen, oxygen, chlorine etc., Now we will discuss how the atoms are held together in a molecule of a carbon compound.The atomic number of carbon is 6. It's electronic configuration is 2,4. So it will have 4 valence electrons.
To attain the stable electronic configuration:
• the carbon should lose the 4 electrons.
• or, it should gain 4 new electrons.
Both the above options are difficult. Let us see the reason:
■ A large amount of energy will be required to remove the four valence electrons. Even if they are removed, the 6 protons in the nucleus will be attracting just 2 electrons. This is not possible. So, removal of 4 electrons will not occur
■ If the carbon atom is to gain 4 electrons, the 6 protons in the nucleus will have to attract and hold 10 electrons in the shells. This is difficult. So gaining of electrons also will not occur
What occurs is the sharing of electrons. This will give rise to covalent bonds between carbon atom and atoms of other elements. We have seen the details about covalent bonds earlier. Let us now draw the covalent bonds in some of the carbon compounds:
■ First we will take Methane (CH4)
We have already seen it when we discussed about covalent bond. The details are presented here again.
• Carbon has an atomic number 6. It’s electronic configuration is 2,4. It has 4 electrons in the outer most shell. It needs four more electrons to attain octet.
• Hydrogen has an atomic number 1. It’s electronic configuration is also 1. It has 1 electron in the outer most shell. It needs one more electron to attain octet.
• We see that both carbon and hydrogen are in ‘need for electrons’. They cannot donate any electrons. So the only solution is to form a covalent bond as shown in fig.8.1 below:
 |
| Fig.8.1 |
• One carbon atom combines with 4 hydrogen atoms. Each of the four hydrogen atoms share one pair of electrons with the carbon atom
• In total, four pairs (that is., eight electrons) are shared. The eight electrons in the pairs, belongs to both the carbon atom and the hydrogen atom.
• The carbon atom now has the required four electrons for octet.
• The hydrogen atom now has the required 2 electrons for octet
• As the pair belongs to both the atoms, they will not be able to move away from each other
• That is., the carbon and four hydrogen atoms will have to always stick together. Thus a bond is formed between the five atoms
• In each bond, there is a sharing of one pair of electrons. So each bond is a 'single bond'. So methane can be represented as shown in fig.8.2(a) below. The 'single lines' between C and H indicates 'single bonds'.
 |
| Fig.8.2 |
• Carbon has an atomic number 6. It’s electronic configuration is 2,4. It has 4 electrons in the outer most shell. It needs four more electrons to attain octet.
• Oxygen has an atomic number 8. It’s electronic configuration is 2,6. It has 6 electrons in the outer most shell. It needs two more electrons to attain octet.
• We see that both carbon and oxygen are in ‘need for electrons’. They cannot donate any electrons. So the only solution is to form a covalent bond as shown in fig.8.3 below:
 |
| Fig.8.3 |
• One carbon atom combines with 2 oxygen atoms. Each of the two oxygen atoms share two pairs of electrons with the carbon atom
• In total, four pairs (that is., eight electrons) are shared. The eight electrons in the pairs, belongs to both the carbon atom and the oxygen atoms.
• The carbon atom now has the required 4 electrons for octet.
• The oxygen atoms now has the required 2 electrons for octet
• As the pair belongs to both the atoms, they will not be able to move away from each other
• That is., the carbon and two oxygen atoms will have to always stick together. Thus a bond is formed between the three atoms
• In each bond, there is a sharing of two pairs of electrons. Thus each bond is a 'double bond'. So carbon dioxide can be represented as shown in fig.8.2(b) above. The 'double lines' between C and O indicates 'double bonds'.
A very large number of carbon compounds
We have seen that many objects that use in our day to day life are made up of carbon compounds. The number of carbon compounds was recently estimated to be nearly three million. That is., thirty lakhs. This is far greater than the total number of compounds formed by all other elements.How is it possible for the carbon to form such large number of compounds?
Let us analyse the reasons:
Reason 1
We know that carbon has 4 electrons in it's outer most shell. That is., it has a valency of 4. This makes it possible to form 3 different types of bonds. They are shown in fig.8.4 below:
 |
| Fig.8.4 |
• The red dots indicate the new electrons which are acquired by sharing.
Let us see each type in detail:
1. In fig.8.4(a), the carbon is in bond with 4 other atoms. Each bond is a single bond. Through this arrangement, 4 new electrons are acquired. Thus octet is achieved.
2. In fig.b, the carbon is in bond with 3 other atoms. The bond with one of them is a double bond. Through this arrangement, 4 new electrons are acquired. Thus octet is achieved.
3. In fig.c, the carbon is in bond with 2 other atoms. The bond with one of them is a triple bond. Through this arrangement, 4 new electrons are acquired. Thus octet is achieved.
■ Thus there are three methods by which a carbon atom can enter into bond with others. The bonds so formed are very strong. The reason for the strong bonds can be explained as follows:
• The size of a carbon atom is small. So the force of attraction between the central nucleus and the outer most electrons will be strong. This gives strong bonds. So the molecules thus formed are very stable.
The chemical properties of the newly formed molecules will depend upon the properties of carbon and also the newly bonded elements.
Reason 2
Carbon has the unique ability to enter into bondage with other carbon atoms.
• Because of this ability, long chains of carbon atoms can be formed. This is shown in fig.8.5(a) below:
 |
| Fig.8.5 |
• The end carbon in a chain may enter into bondage with the first carbon to form a ring. This is shown in fig.c.
■The ability of atoms of an element to combine among themselves and form chains is called catenation. Chains, branched chains and rings are formed because of this property.
• Carbon has the ability to catenate.
• But it is not seen in other elements. Silicon some times forms chains up to a maximum of 8 atoms long. But the molecules thus formed are very reactive.
• We have seen that the carbon bond is very strong and hence stable. So a large variety of carbon compounds are possible.
So we have seen two reasons. The formation of very large number of carbon compounds can be explained using those two reasons.
In the next section, we will see the actual arrangement of atoms in a molecule of Carbon compounds.
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