Chemistry

Chemical Bonding and Molecular Structure

Question:

Define Octet rule. Write its significance and limitations.

Answer:

Octet rule: Atoms of elements combine with each other in order to complete their respective octets so as to acquire the stable gas configuration.
Significance: It helps to explain why different atoms combine with each other to form ionic compounds or covalent compounds.
Limitations of Octet rule:

  • According to Octet rule, atoms take part in chemical combination to achieve the configuration of nearest noble gas elements. However, some of noble gas elements like Xenon have formed compounds with fluorine and oxygen. For example: XeF2, XeF4  etc.
    Therefore, validity of the octet rule has been challenged.
  • This theory does not account for shape of molecules.
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Questions and Answers

Chemical Bonding and Molecular Structure

Q 1.

Elements X, Y and Z have 4, 5 and 7 valence electrons respectively, (i) Write the molecular formula of the compounds formed by these elements individually with hydrogen, (ii) Which of these compounds will have the highest dipole moment?

Answer

Q 2.

What is the effect of the following processes on the bond order in N-, and 02?
(i) N2 → N+2 + e– (ii) 02 → O+2 + e–

Answer

Q 3.

Which of the following statements are correct about CO32- ?
(a) The hybridization of central atom is sp3.
(b) Its resonance structure has one C – O single bond and two C = O double bonds.
(c) The average formal charge on each oxygen atom is 0.67 units.
(d) All C – O bond lengths are equal.

Answer

Q 4.

Briefly describe the valence bond theory of covalent bond formation by taking an example of hydrogen. How can you interpret energy changes taking place in the formation of dihydrogen?

Answer

Q 5.

Is there any change in the hybridisation ofB and N atoms as a result of the following reaction ?  BF3 + NH3 ——-> F3 B.NH3

Answer

Q 6.

Explain why PC15 is trigonal bipyramidal whereas IF5 is square pyramidal.

Answer

Q 7.

(a) How many a and n bonds are present in
ncert-solutions-for-class-11-chemistry-chapter-4-chemical-bonding-and-molecular-structure-34
(b) Why Hf is more stable than H2?
(c) Why is B2 molecule paramagnetic?

Answer

Q 8.

Which of the following statements are not correct?
(a) NaCl being an ionic compound is a good conductor of electricity in the solid state.
(b) In canonical structures there is a difference in the arrangement of atoms.
(c) Hybrid orbitals form stronger bonds than pure orbitals.
(d) VSEPR theory can explain the square planar geometry of XeF4.

Answer

Q 9.

Write Lewis structure of the following compounds and show formal charge on each atom.  HN03, No2, H2so4

Answer

Q 10.

Match the items given in Column I with examples given in Column II.

Column I Column II
(i) Hydrogen bond (a) C
(ii) Resonance (b) LiF
(iii) Ionic solid (c) H2
(iv) Covalent solid (d) HF
  (e) 03
Answer

Q 11.

In which of the following substances will hydrogen bond be strongest?
(a) HCl
(b) H20                                          
(c) HI                                            
(d) H2S

Answer

Q 12.

Which of the following species have the same shape?
(a) C02
(b) CC14                                  
(c) 03                                                
(d) N0–2

Answer

Q 13.

What is an ionic bond? With two suitable examples explain the difference between an ionic and covalent bond?

Answer

Q 14.

Arrange  O2,O2–,O22-, O2+in increasing order of bond energy.

Answer

Q 15.

Match the species in Column I with the bond order in Column II.

Column I , . Column II
(i) NO (a) 1.5
(ii) CO (b) 2.0
(iii) o–2 (c) 2.5
(iv) 02 (d) 3.0
Answer

Q 16.

How is bond order related to bond length of a molecule?

Answer

Q 17.

In N0–3 ion, the number of bond pairs and lone pairs of electrons on nitrogen atom are
(a) 2, 2                                       (b) 3, 1                                           (c) 1,3                                           (d) 4, 0

Answer

Q 18.

Use Lewis symbols to show electron transfer between the following atoms to form cations and anions (a) K and S (b) Ca and O (c) Al and N.

Answer

Q 19.

Explain the diamagnetic behaviour of  P2  molecule on the basis of molecular orbital theory.

Answer

Q 20.

All the C – O bonds in carbonate ion (CO2-3) are equal in length. Explain.

Answer

Q 21.

Write the resonance structures for SO3,NO2 and NO3

Answer

Q 22.

Distinguish between a sigma bond and a pi bond.

Answer

Q 23.

Write the significance of plus and minus sign in representing the orbitals,

Answer

Q 24.

Out of sigma and Π  bonds, which one is stronger and why?

Answer

Q 25.

Predict the shapes of the following molecules using VSEPR theory?
(i) BeCl2(ii) SiCl4

Answer

Q 26.

Why  N2  is more stable than  O2? Explain on the basis of molecular orbital theory.

Answer

Q 27.

Define bond order. How is it related to the stability of a molecule?

Answer

Q 28.

Polarity in a molecule and hence the dipole moment depends primarily on electronegativity of the constituent atoms and shape of a molecule. Which of the following has the highest dipole moment?
(a) C02
(b) HI                                            
(c) H20                                          
(d) S02

Answer

Q 29.

Arrange the following bonds ‘in order of increasing ionic character giving reason.
N-H, F-H, C-H and O-H

Answer

Q 30.

Match the species in Column I with the geometry/shape in Column II.

Column I Column II
(i) H30+ (a) Linear
(ii) HC = CH (b) Angular
(iii) Cl0–2 (c) Tetrahedral
(iv) NH+4 (d) Trigonal bipyramidal
– (e) Pyramidal
Answer

Q 31.

Explain the formation of a chemical bond.

Answer

Q 32.

Define electronegativity. How does it differ from electron gain enthalpy?

Answer

Q 33.

Explain with the help of suitable example polar covalent bond.

Answer

Q 34.

How is bond order related to the stability of a molecule?

Answer

Q 35.

Write the Lewis dot symbols of the following elements and predict their valencies.  (i) Cl (ii) P

Answer

Q 36.

Write the state of hybridisation of boron in  BF3.

Answer

Q 37.

What are Lewis structures? Write the Lewis structure of  H2, BeF2  and  H2O.

Answer

Q 38.

Give the shapes of the following molecules:
(i) AB3  (ii) AB4

Answer

Q 39.

What do you mean by Dipole moment? Draw the dipole diagram of H2O.

Answer

Q 40.

Explain the non linear shape of H2S and non planar shape of PCl3 using valence shell electron pair repulsion theory.

Answer

Q 41.

Why does type of overlap given in the following figure not result in the bond formation?
ncert-exemplar-problems-class-11-chemistry-chapter-4-chemical-bonding-and-molecular-structure-28

Answer

Q 42.

Match the species in Column I with the type of hybrid orbitals in Column II.

Column I Column II
(i) SF4 (a) sp3cf
(ii) if5 (b) d2sp3
(iii) NO2+ (c) sp3 d
(iv) NH4 (d) sp3
  (e) sp
Answer

Q 43.

Write the significance/applications of dipole moment.

Answer

Q 44.

Use molecular orbital theory to explain why the Be2 molecule does not exist.

Answer

Q 45.

Compare the relative stability of the following species and indicate their magnetic properties: O2, O2, O2– (Superoxide),O22- (peroxide)

Answer

Q 46.

Write the type of hybridisation involved in  CH4,C2H4  and C2H2.

Answer

Q 47.

Define covalent bond according to orbital concept?

Answer

Q 48.

Out of bonding and antibonding molecular orbitals, which one has lower energy and which one has higher stability?

Answer

Q 49.

Define antibonding molecular orbital.

Answer

Q 50.

Name the two conditions which must be satisfied for hydrogen bonding to take place in a molecule.

Answer