Carbon is a versatile element. The percentage of carbon present in earth’s crust in form of mineral is 0.02% and in atmosphere as CO, is 0.03%.
All the living things, like plants and animals are made up of carbon-based compounds.
Carbon always forms covalent bonds.
The atomic number of carbons is 6.
C (6) 2 4
It has four electrons in its outermost shell and requires 4 electrons to achieve the inert gas electronic configuration. But carbon cannot form an ionic bond.
How does carbon attain noble gas configuration?
(i) Carbon can attain its stable noble gas configuration in two ways:
It may gain four electrons to form C+ anion. But in that case, it would be difficult for the nucleus with six protons to hold on to ten electrons.
It could lose four electrons to form C cations. But in that case, it would require huge amount of energy which is not energetically favourable.
(ii) Thus, carbon overcomes this problem by sharing its valence electrons with other atoms of carbon or with atoms of other elements The atoms of other elements like hydrogen, oxygen, nitrogen and chlorine also form bonds by sharing of electrons.
Covalent Bond: A covalent bond is formed by sharing of electrons between atoms. In a covalent bond, the shared pair of electrons belongs to the valence shell of both the atoms.
Conditions for formation of a covalent bond:
The combining atoms should have 4 to 7 electrons in their valence shell.
The combining atoms should not lose electrons easily.
The combining atoms should not gain electrons readily.
The difference in electronegativity of two bonded atoms should be low.
Properties of covalent compounds:
Physical state: They are generally liquids or gases. Some covalent compounds may exist as solid.
Solubility: They are generally insoluble in water and other polar solvents but soluble in organic solvents such as benzene, toluene etc.
Melting and boiling points: They generally have low melting and boiling points.
Electrical conductivity: Covalent compounds are generally poor conductor of electricity. This is because the electrons are shared between atoms and no charged particles are formed in these compounds.
Steps for writing the Lewis dot Structures of a covalent compound:
Write the electronic configuration of all the atoms present in the molecule.
Identify how many electrons are needed by each atom to attain noble gas configuration.
Share the electrons between atoms in such a way that all the atoms in a molecule have noble gas configuration.
Keep in mind that the shared electrons are counted in the valence shell of both the atoms sharing it.
Hydrocarbon: compounds made up of hydrogen and carbon are called hydrocarbon.
Electron dot structure of saturated hydrocarbons:
Electron dot structure of unsaturated hydrocarbons:
Ethene: C2H4 Ethyne: C2H2
Cyclic or Closed Chain Hydrocarbons: These are the hydrocarbons which have carbon – carbon closed chain. They are classified as:
Alicyclic hydrocarbons: These are the hydrocarbons which do not have benzene ring in their structures.
Aromatic hydrocarbons: The hydrocarbons which have benzene ring in their structures. When hydrogen bonded to carbon of benzene is substituted with halogens, radicals or other functional groups, the derivatives are called aromatic compounds.
Benzene: It is an aromatic hydrocarbon which has the molecular formula C6H6. It has alternating carbon – carbon single and double bonds.
Benzene can also be represented as:
IUPAC name of hydrocarbon consists of two parts.
Word root: Number of carvons in he longest carbon chain.
(ii) Suffix: it depends on the type of carbon carbon bond, for single vond suffix is -ane; for double bond suffix is ene; and for triple bond suffix is -yne.
Types of Formula for Writing Hydrocarbons:
A Molecular formula: It involves the actual number of each type of atom present in the compound.
Structural formula: The actual arrangement of atoms is written in the structural formula.
Condensed formula: It is the shortened form of the structural formula.
In a hydrocarbon chain, one or more hydrogen atoms is replaced by other atoms in accordance with their valencies.
These are heteroatoms. – These heteroatoms or group of atoms that make carbon compound reactive and decides their properties are called functional groups.
Homologous Series: A series of organic compounds in which every succeeding member differs from the previous one by – CH2 or 14 a.m.u. is called homologous series. The molecular formula of all the members of a homologous series can be derived from a general formula.
Properties of a homologous series: As the molecular mass increases in a series, physical properties of the compounds show a variation, but chemical properties which are determined by a functional group remain the same within a series.
Homologous series of alkanes: General formula: CnH2n+2, where n = number of carbon atoms. CH4, C2H6, C3H8
Homologous series of alkenes: General formula: CnH2n, where n = number of carbon atoms. C2H4, C3H6,C4H8–
Homologous series of alkynes: General formula: CnH2n-2, where n = number of carbon atoms. Č2H2, Č3H4,C4H6