Vidaara.orgClass 11 · Chemistry
CodeVID-C11-04-T1-01
Ionic & Covalent Bonding - Assignment
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Only final answers are given at the end - for full solutions, raise your doubts with your teacher.
Section A - Multiple Choice Questions
5 × 1 = 5 marks
1.
The octet rule was proposed in the work of:
- A.Bohr
- B.Kossel and Lewis
- C.Rutherford
- D.Dalton
2.
Which of these has an incomplete octet?
- A.CH4
- B.BF3
- C.NH3
- D.H2O
3.
Lattice enthalpy is highest for:
- A.NaCl
- B.KCl
- C.MgO
- D.CsCl
4.
The SI-related unit of dipole moment used in chemistry is the:
- A.coulomb
- B.debye
- C.joule
- D.newton
5.
An odd-electron molecule that does not obey the octet rule is:
- A.CO2
- B.NO
- C.N2
- D.HCl
Section B - Short Answer (2 marks)
3 × 2 = 6 marks
6.
State the octet rule and give the exception for hydrogen.
7.
Write the formal-charge formula for an atom in a Lewis structure.
8.
Define lattice enthalpy and state one factor that increases it.
Section C - Short Answer (3 marks)
2 × 3 = 6 marks
9.
State Fajans' rules and use them to compare the covalent character of LiCl and LiF.
10.
Explain why CO2 is non-polar while H2O is polar.
Section D - Long Answer (5 marks)
1 × 5 = 5 marks
11.
Discuss the limitations of the octet rule with one example of each type, and define bond order, bond length and bond enthalpy.
Answer Key
Section A - Multiple Choice Questions
- (B) Kossel and Lewis
- (B) BF3
- (C) MgO
- (B) debye
- (B) NO
Section B - Short Answer (2 marks)
- Atoms tend to attain eight electrons in their valence shell by gaining, losing or sharing electrons; hydrogen needs only a duplet (two electrons).
- FC = (valence electrons) - (lone-pair electrons) - (1/2)(bonding electrons).
- The energy released when one mole of an ionic solid forms from its gaseous ions; it increases with higher ionic charge (or smaller ionic size).
Section C - Short Answer (3 marks)
- Covalency increases with small cation, large anion and high charge. Cl- is larger and more polarisable than F-, so LiCl has greater covalent character than LiF.
- CO2 is linear so the two equal bond dipoles cancel (mu = 0); H2O is bent so its two O-H dipoles add to give a net dipole (about 1.85 D).
Section D - Long Answer (5 marks)
- Incomplete octet (BF3), expanded octet (SF6), odd-electron molecule (NO), and it does not explain shape/energy. Bond order = number of shared pairs; bond length = equilibrium internuclear distance; bond enthalpy = energy to break one mole of bonds. Higher bond order gives shorter, stronger bonds.
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