Carbon and Covalent Bonding
At the beginning of the 19th century, compounds obtained from plants and animals were regarded as organic compounds.
Organic compounds that contain both hydrogen and carbon are called hydrocarbons. These are parent fundamental compounds.
Classification of hydrocarbons
Hydrocarbons are classified on the basis of their structure and bonding.
The given figure shows the classification of hydrocarbons.
Open chain hydrocarbons - An open chain is an arrangement of atoms that does not form a ring, i.e. it has two open ends. It may consist of straight or branched chain compounds.
Open chain hydrocarbons are again classified into two sub-groups.
(a) Saturated open chain hydrocarbons - The saturated (contains only single bonds) open chain hydrocarbons form a homologous series called the paraffin series or the alkane series.
Their formula can be summarised as CnH2n+ 2, where n is the number of carbon atoms in the molecule.
Examples- Methane (CH4), ethane (C2H6),propane (C3H8), Butane (C4H10)
Do You Know?
Alkanes are also known as 'paraffins'. The word ‘paraffin’, which is derived from a Latin word meaning "little activity", means that such compounds are very unreactive.
(b) Unsaturated open chain hydrocarbons - Unsaturated open chain hydrocarbons include the alkene or olefin series, the diene series and the alkyne series.
1. Alkene: The alkene series consists of chain hydrocarbons that contain a double bond between two carbon atoms. The general formula for the series is CnH2n, where n is the number of carbon atoms.
Examples: Ethene (CH2=CH2), Propene (CH3-CH=CH2), Butene (CH3-CH2-CH=CH2)
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Alkenes are also called olefins because they form oily liquids on reaction with chlorine gas.
2. Alkyne: Members of the alkyne series contain a triple bond between two carbon atoms in a molecule. Alkynes have the general formula CnH2n −2.
Examples: Ethyne (HC≡ CH), Propyne (CH3-C≡CH), 2-Butyne (CH3-C≡C-CH3)
Closed Chain Hydrocarbons - The hydrocarbons which contain a closed chain of carbon atoms are called cyclic hydrocarbons. These compounds contain carbon atoms joined in the form of a ring. They are further sub-divided into two sub-groups.
(a) Alicyclic Hydrocarbons - These cyclic compounds contain single bonds. These are closed chain or cyclic compounds but they behave more like aliphatic or open chain compounds in spite of their rings.Upon cyclisation, an alkane hydrocarbon chain would result in the formation of alicyclic compounds.
(b) Aromatic Compounds - These organic compounds contain at least one Benzene ring. Aromatic compounds have alternate single and double bonds. The substitution of one or all hydrogen atoms in a Benzene ring can form aromatic compounds.
Do You Know?
Aromatic compounds get their name from the fact that many of these compounds have a sweet scent.
We know that a majority of substances used by us daily, from paper and plastics to coal and petrol, are all made up of carbon. Food grains, pulses, medicines, cotton, synthetic fibres, wood etc. are all made up of carbon. Carbon is also a major part of all living things. In air, it is present as carbon dioxide and comprises around 0.03% of the total air.
Let us study about carbon and its bonding in its compound in more detail.
Carbon is a non-metal having the symbol ‘C’ and atomic number six. Since the atomic number of carbon is six, its electronic configuration is 2, 4. This means that carbon contains two electrons in K shell and 4 electrons in L shell (outermost shell). Hence, it has four electrons in its valence shell.
Since carbon has four electrons in its valence shell, it needs four more electrons to complete its octet. Therefore, it is a tetravalent element.
In order to complete its octet i.e., to attain its noble gas configuration and to stabilize itself, carbon can:
- Either lose four electrons to form C4+ or gain four electrons to form C4−. This, however, requires a lot of energy and would make the system unstable.
The bonds that are formed by sharing electrons are known as covalent bonds. Covalently bonded molecules have weak intermolecular forces, but intramolecular forces are strong.
Carbon has four valence electrons and needs four more electrons to complete its octet. Therefore, it is capable of bonding with four other atoms of carbon or atoms of other elements having a valency of 1.
For example, the molecule, methane can be formed with hydrogen (H) atoms that have only one electron in its K shell. To attain the noble gas configuration, it combines with four hydrogen atoms as shown in the figure.
Now, let us study the properties of carbon compounds.
- Covalent bonds are made by atoms by sharing their electrons. Formation of ions does not take place in this process. In addition, these compounds do not have any extra electrons. Hence, covalent compou…
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