Chemical Bond

♦ Atoms combine to form molecules.
♦ Formation of chemical bond involves redistribution of electrons.

♦ Ionic Bond: "The chemical bond formed by the complete transfer of one or more electrons from one atom to other".
                Eg: NaCl, MgO
♦ Covalent Bond: "The bond formed by the sharing of electrons between two atoms".
                Eg: H2, Cl2, F2, H2O
♦ Octet configuration: "The filling up of valence orbital with 8 electrons".
♦ As the atoms approach each other, the attractive forces between electrons of one atom and the nucleus of other atom increases, results in the decrease of combined potential energy of combined atoms.
♦ At the critical internuclear distance, the energy of the molecule (or) combined atoms is less than the sum of the energies of individual atoms and thus a chemical bond is formed.

Potential- Energy Level Diagram:

♦ Zero group elements have stable electronic configuration having 2 (or) 8 electrons.

♦ A covalent bond is formed by the overlap of two pure atomic orbitals (or) two hybridised orbitals (or) one hybridized and one atomic orbital.

♦ Strong bond is formed by the maximum overlap of orbitals.

♦ Sigma-bond: End-on-end overlap of orbitals lead to the formation of sigma bond. It is formed by the overlap of s-s orbitals, p-p orbitals and s-p orbital overlap.

♦ Pi-bond: Partial overlap of orbitals lead to the formation of pi (π) bond.

♦ Sigma bond is stronger than pi-bond, sigma bond exists independently.

       Eg: H2, HCl, Cl2, CH4

♦ π-bond has no independent existence. It exists only after the formation of σ bond.

♦ In a double bond, one sigma and one π bond are present.

        Eg: C2H4, O2, CO2, etc.,

♦ In a triple bond, one sigma and two pi-bonds are present.

        Eg: N2, C2H2, HCN etc.,

♦ In a co-ordinate covalent bond, both the electrons are supplied by one atom and shared between two atoms.

♦ The primary requirement for the formation of a covalent bond is that one atom should have a lone pair of electrons (with octet configuration) to donate and another atom should have an empty orbital to receive it.

♦ Molecules having linear structure are

      Eg: CO2, BeCl2, C2H2, HCN etc.,

♦ Molecules having pyramidal structure are

      Eg: NH3, PCl3, PH3, ....

♦ Molecules having double bond are

      Eg: O2, CO2, C2H4, ....

♦ Molecules having triple bond are

      Eg: N2, HCN, C2H2...

♦ Water molecule have "V" - shape.

♦ PCl5 has trigonal bi-pyramidal shape.

Questions

SECTION - II

Very Short Answer Questions (1 Mark Each)

1. Draw the shape of water molecule.

2. Name the two molecules having pyramidal shape?

3. What is the shape of ammonia molecule? Draw it and explain.

4. Give three examples of molecules having a double bond?

5. Give two examples of molecules having a triple bond?

6. Name two molecules having p-p overlapping?

7. Which orbitals can form pi (π) bond?

8. What is the shape of carbon dioxide molecule?

9. Show the electron dot structure of H2 molecule?

10. What are multiple covalent bonds? Give examples?

SECTION - III

Long Answer Questions (4 Marks Each)

1. Explain the formation of a double-bond with example?

2. Explain the formation of co-ordinate covalent bond?

3. Explain s–p overlap with examples?

4. Explain the formation of triple bond in Nitrogen molecule?

(or)

Explain the formation of multiple bond with an example?

5. Discuss the type of overlaps that are possible with s and p orbitals.

SECTION - IV

DIAGRAMS (5 Marks Each)

1. Draw the bond formation of Hydrogen Chloride and Nitrogen molecules in a diagram.

2. Draw the diagram showing the formation of a double bond (oxygen molecule)?

3. Draw the diagram showing the formation of p–p overlap in fluorine molecule.