Chemistry

Chemical Bonding and Molecular Structure

Question:

Describe the hybridisation in case of PCl5. Why are the axial bonds longer as compared to equatorial bonds?

Answer:

The ground state and excited state outer electronic configurations of phosphorus (Z = 15) are:
ncert-solutions-for-class-11-chemistry-chapter-4-chemical-bonding-and-molecular-structure-37
Phosphorus atom is  sp3  d hybridized in the excited state. These orbitals are filled by the electron pairs donated by five Cl atoms as:
ncert-solutions-for-class-11-chemistry-chapter-4-chemical-bonding-and-molecular-structure-38
The five sp3 d hybrid orbitals are directed towards the five comers of the trigonal bipyramidal. Hence, the geometry of PCl5 can be represented as:
There are five P-Cl sigma bonds in PCl5. Three P-Cl bonds lie in one plane and make an angle of 120 ° with each other.
ncert-solutions-for-class-11-chemistry-chapter-4-chemical-bonding-and-molecular-structure-39
These bonds are called equatorial bonds. The remaining two P-Cl bonds lie above and below the equatorial plane and make an angle of 90 ° with the plane. These bonds are called axial bonds.
As the axial bond pairs suffer more repulsion front the equatorial bond pairs, axial bonds are slightly longer than equatorial bonds.

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Chemical Bonding and Molecular Structure

Q 1.

Assertion (A): Though the central atom of both NH3 and H20 molecules are sp3 hybridised, yet H – N – H bond angle is greater than that of H – O – H.
Reason (R): This is because nitrogen atom has one lone pair and oxygen atom has two lone pairs.
(a) A and R both are correct, and R is the correct explanation of A.
(b) A and R both are correct, but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A and R both are false.

Q 2.

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

Q 3.

State the types of hybrid orbitals associated with (i) P in PCl5  and (ii) S in  SF6

Q 4.

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?

Q 5.

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

Q 6.

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

Q 7.

Which is more polar CO2  or  N2O? Give reason.

Q 8.

(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?

Q 9.

Although both CO2 and H2O are triatomic molecules, the shape of H2O molecule is bent while that of CO2 is linear. Explain this on the basis of dipole moment.

Q 10.

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.

Q 11.

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

Q 12.

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

Q 13.

Assertion (A): Among the two O – H bonds in H20 molecule, the energy required to break the first O – H bond and other O – H bond is the same.
Reason (R): This is because the electronic environment around oxygen is the same even after breakage of one O – H bond.
(a) A and R both are correct, and R is the correct explanation of A.
(b) A and R both are correct, but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A and R both are false.

Q 14.

Draw the Lewis structures for the following molecules and ions:
H2S, SiCl4 ,  BeF2, C032-, HCOOH

Q 15.

Write the favourable factors for the formation of ionic bond.

Q 16.

Define the bond-length.

Q 17.

Write the significance/applications of dipole moment.

Q 18.

The skeletal structure of  CH3COOH  as shown below is correct, but some of the bonds are shown incorrectly. Write the correct Lewis structure for acetic acid.
ncert-solutions-for-class-11-chemistry-chapter-4-chemical-bonding-and-molecular-structure-12

Q 19.

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

Q 20.

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

Q 21.

Define antibonding molecular orbital.

Q 22.

In which of the following molecule/ion all the bonds are not equal?
(a) XeF4                                  
(b) BF4                                        
(c) C2H4                                    
(d) SiF4

Q 23.

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

Q 24.

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

Q 25.

Explain why CO2-3 ion cannot be represented by a single Lewis structure. How can it be best represented?

Q 26.

Define Octet rule. Write its significance and limitations.

Q 27.

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

Q 28.

Which out of NH3 and NF3 has higher dipole moment and why?

Q 29.

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

Q 30.

What is the total number of sigma and pi bonds in the following molecules?
(a) C2 H2 (b) C2 H4

Q 31.

Considering X-axis as the intemuclear axis which out of the following will not form a sigma bond and why? (a) Is and Is (b) Is and  2px  (c)  2py  and 2py (d) Is and 2s

Q 32.

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

Q 33.

Define hydrogen bonds. Is it weaker or stronger than the van der Waals forces?

Q 34.

Why  B2  is paramagnetic in nature while C2 is not?

Q 35.

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

Q 36.

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

Q 37.

Account for the following:
(i) Water is a liquid while H2S is a gas
(ii) NH3 has higher boiling point than PH3.

Q 38.

Using molecular orbital theory, compare the bond energy and magnetic character of 0+2 and O2

Q 39.

Q 40.

Write Lewis dot symbols for atoms of the following elements: Mg, Na, B, O, N, Br.

Q 41.

Explain with the help of suitable example polar covalent bond.

Q 42.

Arrange the bonds in order of increasing ionic character in the molecules: LiF, K2O, N2, SO2 and ClF3.

Q 43.

Write the important conditions required for the linear combination of atomic orbitals to form molecular orbitals.

Q 44.

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

Q 45.

Which of the following has larger bond angle in each pair?
(i) CO2, BF3 (ii) NH3, CH4

Q 46.

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

Q 47.

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

Q 48.

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

Q 49.

Explain why BeH2   molecule has a zero dipole moment although the Be-H bonds are polar.

Q 50.

Species having same bond order are
(a) N2                                            
(b) N2                                              
(C) F+2                                            
(d) o2