What are Carbon Compounds?
Carbon compounds are defined as chemical substances containing carbon. More compounds of carbon exist than any other chemical element except for hydrogen.
- Carbon is very reactive. It forms a huge number of compounds with many other elements.
- Compounds containing carbon outnumber the compounds of all the other elements.
- Carbon is derived from the word “carbo” meaning coal.
- Atomic number - 6, Atomic mass - 12, Electronic configuration - 2, 4, Valency - 4
- The compounds obtained from 'Carbon' are widely used.
Example: Clothes, medicines, books, food, fertilizer, fuel etc. all living structures are carbon-based.
- The amount of carbon present in the earth's crust and in the atmosphere is quite less. The earth's crust has only 0.02% carbon in the form of mineral (like carbonates, hydrogen-carbonates, coal, and petroleum) and the atmosphere has 0.03% of carbon dioxide. In spite of this small amount of carbon available in nature, the importance of carbon seems to be immense.
Application of Carbon
- Carbon forms a large number of compounds with hydrogen which are known as Hydrocarbons.
- In addition to hydrogen, carbon compound may also contain some other elements such as oxygen, halogen, nitrogen, phosphorus, sulphur etc.
- The number of compounds of carbon is more than three million which is much larger than the compounds formed by all other elements put together.
Types of Carbon Compounds
1. Saturated Carbon Compounds
These are the compounds in which various carbon atoms in a chain or a ring are linked together by single bonds only. Alkanes are the most common examples of saturated chain carbon compounds. Ethane is a member of the alkane family whose structure is drawn below:
2. Unsaturated Carbon Compounds
These are the compounds in which various carbon atoms in a chain or a ring are linked together by double or triple bonds. Alkenes (where carbon atoms are linked through double bonds) and alkynes (where carbon atoms are linked through triple bonds) are the most common examples of unsaturated chain carbon compounds. Ethene is a member of the alkene family whose structure is drawn below:
Versatile Nature of Carbon
About three million (or thirty lakh) compounds of carbon are known. The existence of such a large number of organic compounds is due to the following characteristic features of carbon.
(a) Catenation (Tendency to form Carbon-Carbon bond)
Carbon has a unique feature of forming long carbon chains i.e. it attaches with other carbon atoms to form long carbon chains. This property is known as catenation.
- The self linking ability of carbon to combine with other atoms of carbon to form long-chain, branched-chain and closed ring structures is called catenation.
- Carbon has the maximum tendency for catenation in the periodic table. This is because of strong carbon-carbon bonds as compared to other atoms and their small size.
- When two or more carbon atoms combine with one another, they form different types of the chain such as:
(i) Straight chains
(ii) Branched chains
(iii) Closed chain or ring chain
Types of the Carbon Chain
(b) Tetravalency of Carbon
- The atomic number of carbon is 6.
- The electronic configuration of the carbon atom is 2, 4.
- It has four electrons in the outermost shell, therefore its valency is four. Thus, carbon forms four covalent bonds in its compounds.
Formation of Methane Molecule
(c) Tendency to form Multiple Bonds
Due to its small size, carbon can easily form double or triple bonds (called multiple bonds) with itself and with the atoms of other elements such as nitrogen, oxygen, sulphur etc.
Compounds having the same molecular formula but different structural formulae are known as isomers and the phenomenon of the existence of isomers is termed isomerism.
What is Covalent Bond?
A chemical bond formed between two atoms of the same element or two atoms of different elements by sharing of electrons is called a covalent bond.
Covalent Bond Formation
Necessary conditions of the formation of Covalent Bond:
- The combining atoms should have a nonmetallic character.
- The combining atoms should contain 4 to 7 electrons in their respective valence shell.
- In hydrogen, there is only 1 valence electron, but it also forms a covalent bond.
- The combining atoms need 1, 2, 3 or 4 electrons to complete their octet (hydrogen completes its duplet).
- The combining atoms should contribute an equal number of electrons to form pair of electrons to be shared.
- After sharing the pair of electrons each combining atoms should attain a stable electronic configuration like its nearest noble gas.
Bonding in Carbon Compounds
Carbon forms covalent bonds in its compounds with other atoms. In each compound, the valency of carbon is four i.e., carbon has a tetravalent character.
Why does a carbon atom form only a covalent bond?
- The atomic number of carbon is 6 and the first shell contains just two electrons and the second shell (Outermost shell) contains four electrons.
- The carbon atom can attain the noble gas configuration by sharing its valence electrons with other atoms of carbon or with atoms of other elements and form a covalent bond.
Try yourself:Why does carbon form compounds mainly by covalent bonding?
Carbon has 4 electrons in its valence shell. To attain stability, it should either gain 4 electrons or lose 4 electrons. It cannot lose 4 electrons as it involves a lot of energy. Also, it cannot gain 4 electrons because the nucleus cannot hold on to the four extra electrons added. Therefore, to complete the octet, it shares 4 electrons with other atoms. That is why, carbon forms compounds mainly by covalent bonding.
Characteristics of Covalent Bond & Covalent Compounds
- A covalent bond is formed by the mutual sharing of electrons.
Note: Shared pair of electrons is also called a bonding pair of electrons.
- Physical State: The covalent compounds are generally gases or liquids, but compounds with high molecular masses are solids.
Example: Urea, Glucose, Naphthalene (solids); Water, ethanol, benzene (liquids); Methane, chlorine, hydrogen, oxygen (gases).
- Melting and boiling points: Covalent compounds have low melting and low boiling points because intermolecular forces (cohesive forces) in covalent compounds are weaker than those in ionic compounds.
Note: Some exception like diamond and graphite which are covalent solids have very high M.P. & B.P.
- Solubility: Covalent compounds generally dissolve readily in organic solvents but they are less soluble in water.
Example: Naphthalene which is an organic compound dissolves readily in organic solvents like ether but is insoluble in water. However, some covalent compounds like urea, glucose, sugar etc. are soluble in water. Some polar covalent compounds like ammonia and hydrochloric acid are soluble in water.
- Conductivity: Covalent compounds do not conduct electricity because they contain neither the ions nor free electrons necessary for conduction, So they do not conduct electricity
Example: Covalent compounds like glucose, alcohol, carbon tetrachloride do not conduct electricity.
Classification of Covalent Bond
On the basis of the number of electrons shared by two combining atoms, the covalent bond are of three types:
(a) Single Covalent Bond
- A single covalent bond is formed by the sharing of one pair of electrons between the two atoms. It is represented by one short line (—) between the two atoms.
Example: H-H, Cl -Cl, H-Cl, CH3-CH3.
(b) Double Covalent Bond
- A double covalent bond is formed by the sharing of two pairs of electrons between the two combining atoms. It is represented by putting (=) two short lines between the two bonded atoms.
Examples: O = O (O2), CO2 (O = C = O), H2C = CH2
(c) Triple Covalent Bond
- A triple bond is formed by the sharing of three pair of electrons between the two combining atoms. It is represented by putting three short line (≡) between two bonded atoms.
Example: N2 (N≡N), CH≡CH.
Formation of Covalent Compounds
- Hydrogen molecule (H2)
A molecule of hydrogen is composed of two H-atoms.
The electronic configuration of H-atom is:
Shell K: 1 Electron - Incomplete Duplet (Unstable)
Shell K: 2 Electron - Complete Duplet (Stable)
H-H Bond in terms of energy shells (orbits)
H-H Bond Formation
Chlorine molecule (Cl2)
The atomic number of chlorine is 17, thus there are 17 electrons in an atom of chlorine.Electronic configuration of Cl atomElectronic configuration of Ar atomChlorine atom needs one electron more to complete its octet
Cl-Cl bond in terms of energy shell orbits
Cl2 molecule formation
- Hydrochloric acid (HCl)
H atom has one valence electron. It needs 1 electron more to complete its duplet and the chlorine atom has 7 valence electrons. It needs 1 electron more to complete its octet and acquire a stable electronic configuration, (2, 8, 8) like the noble gas argon.
HCl molecule formation
- Oxygen molecule(O2)
The atomic number of the O atom is 8. There is 6 electron in the valence shell of an oxygen atom and it needs 2 more electrons to attain the nearest stable inert gas Neon (2, 8) configuration:O2 molecule formation
- Nitrogen molecule (N2)
The atomic number of nitrogen is 7 and its electronic configuration is K(2), L(5). It needs 3 electrons more to complete its octet like noble gas neon (2, 8).
Ammonia molecule (NH3)
The atomic number of N is 7. Its electronic configuration is (2, 5), there are 5 electrons in its valence shell. It needs 3 electrons more to complete its octet like noble gas neon (2, 8).
Ammonia Molecule Formation
- H2O molecule
The electronic configuration of hydrogen is K (1) and that of oxygen is K(2) L(6). Thus, each hydrogen atom requires one and the oxygen atom requires two more electrons to achieve the stable electronic configuration.
H2O Molecule Formation CO2 molecule
The atomic number of C is 6 and the electronic configuration of C is K(2), L(4) and that of oxygen is K(2), L(6) thus each carbon atom requires 4 and the oxygen atom requires two more electrons to achieve the stable electronic configuration.CO2 Molecule Formation
- CH4 molecule
Methane is a covalent compound containing 4 covalent bonds. It contains one carbon atom and four hydrogen atoms covalently bonded to the central carbon atom.
CH4 Bond Formation
Carbon Tetrachloride molecule (CCl4)The electronic configuration of carbon and chlorine atoms are (2, 4) and (2, 8, 7) respectively. The carbon atom needs four electrons and the chlorine atom needs one electron more to attain the stable electronic configuration.CCl4 Molecule Formation Ethylene or Ethene molecule (C2H4)The electronic configuration of the carbon atom is 2, 4. There are 4 valence electrons in one C atom. Each H atom contains 1 valence electron. Thus, there are 12 valence electrons present in the ethene molecule.
Ethene Molecule Formation
- Acetylene or Ethyne molecule (C2H2)
A carbon atom forms a triple covalent bond with another carbon atom and a single covalent bond with a hydrogen atom.
Ethyne molecule formation
Non-Polar & Polar Covalent Compounds
- Non-polar covalent bond
A covalent bond formed between two atoms of the same element or the same electronegativity is called a nonpolar covalent bond.
Example: H2, N2, O2, Cl2 etc.
- Polar covalent bond
The covalent bond formed between the atoms of two elements having different electronegativities is called a polar covalent bond. The molecules in which the atoms are bonded by a polar covalent bond are called polar molecules.
Note: In a polar covalent bond, the shared pair of electrons lies more toward the atom which is more electronegative.
Example: HCl, H2O & NH3
Table: Differences between ionic and covalent compoundsOrganic Compounds
The chemical compounds which are present in living organisms (plant and animal) are called organic compounds. The belief that the formation of organic compounds was possible only in plants and animals led the scientists of early days to propose that the Vital Force was necessary for the formation of such compounds. But the experimental work of Friedrich Wohler (German chemist) denied the idea of vital force when he prepared urea in his laboratory. (urea is an organic compound and waste product of urine).
Try yourself: Which of the following statements are usually correct for carbon compounds? These
(i) Are good conductors of electricity.
(ii) Are poor conductors of electricity.
(iii) Have strong forces of attraction between their molecules.
(iv) Do not have strong forces of attraction between their molecules.
Carbon forms mostly covalent bonds as accepting and donating four electrons is very difficult. Covalent compounds are poor conductors of electricity and they do not have strong forces because a covalent bond is weaker than an ionic bond. Hence, option D is the correct answer.