Carbon and its compounds
Revision Notes
• Properties of Carbon
• The element carbon is non-metal. Its symbol is C.
• 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.
Electronic configuration:
K L
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.
i.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.
ii.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.
Examples:
(i) H2
(ii) O2
(iii) N2
• Hydrocarbon: compounds made up of hydrogen and carbon are called hydrocarbon.