CARBON AND ITS COMPOUNDS

CARBON :-

Carbon is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth’s crust.

Bonding in Carbon: The Covalent bond, Electron dot structure, Physical properties of organic compounds, Allotropes of Carbon.

Covalent Bond: The atomic number of carbon is 6. Its electronic configuration is 2, 4. It requires, 4 electrons to achieve the inert gas electronic configuration. But carbon cannot form an ionic bond.                                                    

It could gain four electrons forming C4- cation. But it would be difficult for the nucleus with six protons to hold on to ten electrons.

It could lose four electrons forming C4+ cations. But it requires a large amount of energy to remove four electrons.

Thus, carbon overcomes this problem by sharing of its valence electrons with other carbon atoms or with atoms of other elements.   The bond formed by mutual sharing of electron pairs between two atoms in a molecule is known as Covalent Bond.

Types of Covalent Bond:

• Single Covalent Bond: When a single pair of electrons are shared between two atoms in a molecule. For example; F2, Cl2, H2 etc.
• Double Covalent Bond: When two pairs of electrons are shared between two atoms in a molecule. For example; O2, CO2 etc.
• Triple Covalent Bond: When three pairs of electrons are shared between two atoms in a molecule. For example; N2 etc.

Electron Dot Structure: The electron dot structures provides a picture of bonding in molecules in terms of the shared pairs of electrons and octet rule.

Formation of Hydrogen Molecule
Atomic number of Hydrogen = 1
Number of valence electrons = 1

No

Formation of CH4 Molecule
Atomic number of Carbon = 6 [2, 4]
Number of valence electrons = 4
Atomic number of Hydrogen = 1
Number of valence electrons = 1

Formation of CO2 Molecule
Atomic number of Carbon = 6 [2, 4]
Number of valence electrons = 4
Atomic number of Oxygen = 8 [2, 6]
Number of valence electrons = 6

Formation of H2S Molecule
Atomic number of Sulphur = 16 [2, 8, 6]
Number of valence electrons = 6

Physical Properties of Organic Compounds
Most of the organic compounds have low boiling and melting point, due to the weak force of attraction (i.e., the inter-molecular force of attraction) between these molecules.
Most carbon compounds are poor conductors of electricity, due to the absence of free electrons and free ions.

Compounds	M.P. (K)	B.P. (K)
Acetic acid (CH3COOH)	290	391
Chloroform (CHCl3)	209	334
Ethanol (CH3CH2OH)	156	351
Methane (CH4)	90	111

Allotropes of Carbon
Allotropy: The phenomenon in which the element exists in two or more different physical states with similar chemical properties are called Allotropy.

Carbon has Three Main Allotropes

• Diamond: In this, carbon, an atom is bonded to four other atoms of carbon forming three-dimensional structures. It is the hardest substance and an insulator. It is used for drilling rocks and cutting. It is also used for making jewellery.                      
  
  
  
• Graphite: In this, each carbon atom is bonded to three other carbon atoms. It is a good conductor of electricity and used as a lubricant.                                                         
  
  
  
• Buckminster Fullerene: It is an allotrope of the carbon-containing cluster of 60 carbon atoms joined together to form spherical molecules. It is dark solid at room temperature.                                                    Versatile nature of Carbon, Hydrocarbons, Isomerism, Homologous series, Functional groups, Nomenclature of functional groups.                                        
  
  
  

• Versatile Nature of Carbon: The existence of such a large number of organic compounds is due to the following nature of carbon,

  • Catenation
  • Tetravalent nature.

  (i) Catenation: The self linking property of an element mainly carbon atom through covalent bonds to form long straight, branched and rings of different sizes are called Catenation.
  This property is due to

  • The small size of the carbon atom.
  • The great strength of the carbon-carbon bond.

  Carbon can also form stable multiple bonds (double or triple) with itself and with the atoms of other elements.
  Straight Chain
  
  Branched Chain
  
  Rings
  

  (ii) Tetravalent Nature: Carbon has valency of four. It is capable of bonding with four other atoms of carbon or some other heteroatoms with single covalent bond as well as double or triple bond.
  

  Hydrocarbons: Compounds of carbon and hydrogen are known as hydrocarbons.
  For example; Methane (CH4), Ethane (C2H6), Ethene (C2H4), Ethyne (C2H2) etc.
  

  Saturated Hydrocarbon (Alkanes): General formula is CnH2n+2.
  n = number of carbon atoms.
  In this, the carbon atoms are connected by only a single bond.
  For example; Methane (CH4), Ethane (C2H6) etc.
  

  Unsaturated Hydrocarbons
  Alkenes: General formula is CnH2n, where n = number of carbon atoms.
  In this, the two carbon atoms are connected by double bond.
  

  Alkynes: General formula is CnH2n-2, where n = number of carbon atoms. In this, the two carbon atoms are connected by triple bond.
  

  Electron Dot Structure of Hydrocarbons