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Carbon is the most important biomolecule essential to sustain life and is found in nature in most abundance. In the earth's crust, 0.02% of carbon exists in the form of minerals whereas in the air it is 0.03%. Carbon can combine with other elements and form different compounds that are seen in living organisms and nonliving things.
Hence, carbon is an essential element in the world of chemistry and has broadly categorized the subject into two parts- Organic chemistry (devoted to carbon-containing compounds) and Inorganic chemistry (chemistry of non-carbon containing compounds). All living organisms have carbon in them hence are studied under organic chemistry.
| Table of Content |
Key Terms: Electronic Configuration, Small Size, Electronegativity, Tetravalency, Ionization Enthalpy, Catenation, Absent D-Orbital
What Is Carbon?
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Carbon is denoted by the letter ‘C’. It is a p- block element and is the first member of group 14 elements of the periodic table.
- The atomic number of carbon is 6 and its atomic mass is 12.01 g/mol.
- It is tetravalent, and non-metallic in nature. Its outer four electrons pair with other atoms and form covalent chemical bonds.
- The oxidation state of carbon is +4, however, sometimes it also forms +2 and 0 oxidation states in inorganic compounds and carbonyls.
Classification Of Carbon
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Carbon is classified into two groups based on the number of bonds it forms with other carbon atoms in a compound formation.
- The two major categories are: Saturated Carbon and Unsaturated Carbon compounds.
Saturated Carbon
The carbon compounds in which various carbon atoms are linked in a chain or a ring by a single bond are called saturated carbon compounds. This type of carbon bonding is shown by alkanes. Eg: ethane, butane.
- H—CH2—CH2—H (structure of ethane)
- H—CH2—CH2—CH2—CH2—H (structure of butane)
Unsaturated Carbon
The carbon compounds in which various carbon atoms are linked in a chain or a ring by double or triple bond are called unsaturated carbon compounds. This type of carbon bonding is shown by alkenes and alkynes. Eg- ethene, butyne.
- H—CH=CH—H (structure of ethene)
- CH3—C≡C—CH3 (structure of butyne)
Electronic Configuration Of Carbon
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- Carbon is a tetravalent atom with four electrons in its outermost shell. It forms covalent bonds.
- The electronic configuration of carbon can be calculated by following the Hund's Rule:
- Atomic number of C= 6
- Ground State = 1s2 2s2 2p2
- Excited state = 1s2 2s1 2p3
Anomalous Behavior Of Carbon
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Carbon is the first element of group 14. Hence, unlike all others, it possesses some different properties from the other elements of group 14 and shows anomalous behavior. It is due to its small size, high electronegativity, tetravalent property, catenation and high ionization enthalpy, and absence of d-orbitals. We will discuss all these topics in detail further below.
Small Size
Carbon has an exceptionally small atomic size which makes it easier to make more bonds and show stability. It forms stable compounds with other elements due to its small size. The nucleus can hold bonded and non-bonded electrons. Carbon has only four electrons in its outermost shell and hence is also called half filled. The valency of carbon is 4.
Electronegativity
Carbon is highly electronegative i.e. tends to attract electrons toward itself. Being small-sized and highly electronegative, it forms multiple pâ¼-pâ¼ bonds with itself or other elements of small size (C=C, C ≡ C, C = O, C = S, and C ≡ N). due to its ability to form pâ¼-pâ¼ bonds and catenation, it shows allotropic forms.
Absence of d-orbital
Carbon contains only s and p- orbitals that are used for bonding and therefore it can accommodate only 4 pairs of electrons in its valence shell. Due to this, the maximum valency of carbon is 4 and it is highly stable.
Other elements of group 14 have d- orbitals and hence can expand their covalency to 6. They have a tendency to form dâ¼-pâ¼ bonds. But this property decreases down the group due to an increase in size.
Tetravalent property
Carbon has 4 electrons in its outermost shell as it has only four valence orbitals one 2s and three 2p. Hence it requires more electrons to complete its octet. Carbon hence bonds with four more monovalent atoms. Carbon combines with elements like oxygen, nitrogen, and hydrogen to form complex compounds that are essentially used. This is called the tetravalency of carbon.
Catenation
The tetravalent property of carbon gives it the tendency to interlink with other carbon atoms through covalent bonds and form rings and chains. C—C bonds are very strong. This property is called catenation. As we move down the group, due to an increase in size and decreased electronegativity, the tendency to show catenation decreases. The order of catenation is C > > Si > Ge ≈ Sn. Lead does not show catenation.
Read more:
| Topic Related Concepts | ||
|---|---|---|
| Allotropes of Carbon | Carbon Dioxide | MCQ on P block elements |
| Group 15 Elements | Rate Determining Step | Preparation of DibenzalAcetone |
Previous Year Questions
- In case of nitrogen, NCl3 is possible but not NCl5 while in case of phosphorus, PCl3 as well as PCl5 are possible. It is due to
- Which one of the following does not produce O2 as the only gaseous product on heating?
- Which one of the following forms a vortex ring?
- NH3 has a much higher b.p. than PH3 because
- Gold is dissolved in aqua-regia to form water, AuCl−4 and Y.X and Y are respectively
- The most stable hydride is
- Nitrogen forms stable N2 molecule but phosphorus is converted to P4 from P2 because
- PCl5 is possible but NCl5 does not exist :
- With excess of water, both P2O5 and PCl5 give
- When A is bubbled into aqueous CuSO4 solution copper phosphide and C are formed, B and C are respectively
Things to Remember
- Carbon is the first member of group 14 elements.
- It is present in the form of allotropes like diamond and graphite. Diamond is the hardest substance known.
- It shows different properties (anomalous behavior) compared to other group 14 elements.
- The different trends and anomalous behavior of carbon is due to its small size, high electronegativity, catenation, absent d-orbital and tetravalent properties.
- Carbon is an essential component of all living systems.
Sample Questions
Ques. Why does the covalency of carbon not expand beyond four? (2 marks)
Ans. Carbon contains only s and p- orbitals that are used for bonding and therefore it is able to accommodate only 4 pairs of electrons in its valence shell. Due to this, the maximum valency of carbon is 4. Other elements of group 14 have d- orbitals and hence can expand their covalency to 6.
Ques. Why Pb and Sn cannot form pâ¼-pâ¼ multiple bonds? (2 marks)
Ans. Only carbon in the group 14 elements has relatively small size and high electronegativity. Hence, it can form pâ¼-pâ¼ multiple bonds. Whereas down the group, the size increases and electronegativity decreases as seen in Pb and Sn, they do not show this type of bonding.
Ques. Why is carbon different from other members of the group? (1 mark)
Ans. Carbon is the first element in group 14 and shows anomalous behavior possessing different properties. It is due to its small size, tetravalency, catenation and high electronegativity.
Ques. What are fullerenes? What is the common name for C60 ? (2 marks)
Ans. Fullerenes are allotropes of carbon. They are made by the heating of graphite in the presence of inert gasses like helium or argon. Fullerenes are the only pure form of carbon because they have smooth structure. Fullerenes are cage-like molecules. The C60 molecule has a shape like a soccer ball and is called Buckminsterfullerene.
Ques. Why does graphite conduct electricity? (2 marks)
Ans. Graphite has a layered structure composed of planar hexagonal rings of carbon atoms. The electrons in graphite are delocalised over the whole sheet and are mobile, therefore, graphite conducts electricity along the sheet.
Ques. Diamond is the hardest substance known. Why? (2 marks)
Ans. Diamond has a crystalline lattice and each carbon atom in the structure of diamond undergoes sp 3 hybridisation and is linked to four other carbon atoms by using hybridized orbitals in tetrahedral fashion. Diamond has a three-dimensional network involving strong C—C bonds. It is very difficult to break extended covalent bonding and, therefore, diamond is the hardest substance on the earth.
Ques. What are the uses of carbon? (4 marks)
Ans. Graphite is an allotrope of carbon, commonly used in pencils.
- Being a good conductor, graphite is used for electrodes in batteries and industrial electrolysis.
- Activated charcoal is used in adsorbing poisonous gasses, water filters to remove organic contamination and in air conditioning systems to control odor.
- Carbon black is used as black pigment in black ink and as filler in automobile tyres.
- Coke is used as a fuel and largely as a reducing agent in metallurgy.
- Diamond is a precious stone and used in jewelry.
- Carbon is also an essential biomolecule and is vital for living.
Ques. Write the electronic configuration of carbon. (1 mark)
Ans. The electronic configuration of carbon is 1s2 2s2 2p2 .
Ques. Write two reasons for anomalous behavior of first elements of each group. (2 marks)
Ans. The first elements of each group show anomalous behavior due to the following properties: 1. Small size as compared to other elements of the group. As we go down the group the size increases. 2. High electronegativity- as we move down the group electropositivity increases.
Ques. Name the different allotropes of carbon. (1 mark)
Ans. Graphite, diamond, fullerenes.
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