Chapter 4

Chemical Bonding

Q1. Define chemical bonds? Explain the types of chemical bonds?


      Definition of Chemical Bond:

                                   The force which holds atoms together in a molecule or a crystal is called a   chemical bond.


                                             Types of Chemical Bonds

      Discovery of Chemical Bond:

                      The first explanation of the nature of chemical bonds was advanced by W. Kossel ( A German Scientist) and G.N Levis (An American Chemist) in 1916. They proposed two major types of chemical bonds.

 Types of Chemical Bond:

 The Ionic or Electrovalent Bond:

                   A bond formed by the transfer of one or more electrons from one atom to another to form ions is called an ionic bond.


 The Covalent Bond:

                 A bond that results when atoms share electrons. Other types of bonds include metallic bonds and hydrogen bonding.


Q2. What is an ionic bond? Explains the formation of Sodium Chloride and Magnesium Oxide?


  Ionic Bond or Electrovalent Bond:

                The attraction that binds oppositely recharged ions together is termed as electrovalent Bond or ionic bond.

 Formation of Sodium Chloride:

                Let us consider the combination of Sodium (Na) and Chlorine(CI) atoms to form common salt, Sodium Chloride( NaCI).In this combination, an atom of Sodium transfers one outermost shell electron and becomes a positive Sodium ion( Na+) and an atom of Chlorine gives that one electron to complete its Octet and become Chloride Negative Ion(CI-).

                            Na          ------->      Na+  +   e-

                  2,8,1                         2,8

                          CI  +   e-  →       CI-

                  2,8,7                           2,8,8

Na+  + CI- → Na+                 CI- or  Na+1    CI-1

                       The attraction that binds Sodium and Chloride ions together is called Electrovalent Bond and the compound Sodium Chloride is called Electrovalent Compound or Ionic Compound.

 Formation of Magnesium Oxide:

                        The formation of Magnesium Oxide from Magnesium and Oxygen. The Magnesium atom has 2 electrons in its valence shell. If these two electrons are lost the Magnesium will become a di positive ion and the Oxygen atom gains these two electrons to complete its octet, and become di negative ion2-. These two oppositely charged ions form Electrovalent Bond and the compound Magnesium Oxide is called Electrovalent Bond.

          12Mg       8O       ------>  Mg+2                                O -2  -------->  Mg2+        O2-

         2,8,2        2,6                   2,8

 Formation of Magnesium Oxide:

           Mg++  +   O--    ----->   Mg++                             O-- Or  Mg+2   O-2


Q3. Write down the characteristics of ionic compounds?

Characteristics of Ionic Compounds:

1. In an ionic bond, it is impossible to say that any two ions bonded to each other to produce a molecule but in the crystals of the ionic compound the oppositely charged ions are mutually surrounded by each other in orderly arrangements. Thus ionic compounds are solids at room temperature.

2. Ionic compounds have high melting and boiling points because of the strong electrovalent bonds existing between the ions.

3. Ionic solids, do not conduct electricity as the ions are not free to move. Once an ionic compound is melted(fused) the ions are free to move and conduct electricity. Similarly, solutions of ionic compounds conduct electricity.

3. Ionic compounds are usually soluble in polar solvents, i.e Solvents of high dielectric constant such as water. But ionic compounds are insoluble in Polar ( Organic) solvents. These solvents have low dielectric constants such as Benzene, Carbon tetrachloride, etc. They are mostly inorganic compounds.


Q4. What is a Covalent Bond? Explains the formation of Chlorine Molecule?

 Covalent Bond Definition:

            The shared pair of electrons which binds atoms in a molecule is known as a covalent bond

 Formation of a Molecule( CI) Chlorine:

                     In a Covalent bond, the shared electron pair is commonly expressed by a single short line(-). For example, the halogens (Chlorine atoms) possess an electronic configuration in which there are 7 electrons in the outermost shell and lacking only one electron in order to attain the structure of inert gas. This structure may be attained by the hydrogen molecule (Chlorine Molecule) when both atoms share one electron for the Bond formation.


               

  Q5. Explain the types of Covalent Bonds?

       Single, Double, and Triple Covalent Bonds:

    Single Covalent Bond:

              In a single covalent bond, only one pair of electrons is shared by the bonded atoms in which each atom has to share one electron. This type of bond is represented by a single short line(-). For example, in the formation of Hydrogen(H2) and Hydrogen Chloride(HCL) molecules, only one pair of electrons is shared.


 Double Covalent Bond:

              In a double covalent bond, Only two pairs of electrons are shared by the bonded atoms and each atom has to share two unpaired electrons. This type of bond is represented by two short lines(=) as shown in the molecules of Oxygen and Carbon dioxide.



Triple covalent bond :

          In Triple Covalent Bond only three pairs of electrons are shared between the bonded atoms and each atom has to share three unpaired electrons. This type of bond is  denoted by three short lines  as shown in the molecules of Nitrogen(N2)  and  Ethane

 (C2H2).


 Formation of Triple Covalent Bonds in Nitrogen and Ethane Molecule.


Q6. Write down the characteristics of the Covalent Compound?

       Characteristics of Covalent Compounds:

1. Compounds with covalent bonds are usually made up of discrete units or molecules with weak intermolecular forces.

2. In the solid state there are big Vander wall forces between the molecules. Hence covalent compounds are gases, liquids, or solids with low melting points. In few cases, three-dimensional co-ordinate structures are formed rather than discrete units hence diamond and silica(SiO2) are covalent but are very hard and have high melting points. Usually, covalent compounds have low melting and boiling points.


3. They are insulators because they do not conduct electricity.


4. Covalent compounds are usually insoluble in polar solvents like water but soluble in organic solvents like Benzene, Ether, Carbon tetrachloride, etc.