NCERT Solutions for Class 11 Chemistry Chemistry Part-1 Chapter 4

Chemical Bonding and Molecular Structure Class 11

Chapter 4 Chemical Bonding and Molecular Structure Exercise Solutions

<< Previous Chapter 3 : Classification of Elements and Periodicity in Properties Next Chapter 5 : States of Matter >>

Exercise : Solutions of Questions on Page Number : 129

Q1 :  

Explain the formation of a chemical bond.


Answer :

A chemical bond is defined as an attractive force that holds the constituents (atoms, ions etc.) together in a chemical species.

Various theories have been suggested for the formation of chemical bonds such as the electronic theory, valence shell electron pair repulsion theory, valence bond theory, and molecular orbital theory.

A chemical bond formation is attributed to the tendency of a system to attain stability. It was observed that the inertness of noble gases was because of their fully filled outermost orbitals. Hence, it was postulated that the elements having incomplete outermost shells are unstable (reactive). Atoms, therefore, combine with each other and complete their respective octets or duplets to attain the stable configuration of the nearest noble gases. This combination can occur either by sharing of electrons or by transferring one or more electrons from one atom to another. The chemical bond formed as a result of sharing of electrons between atoms is called a covalent bond. An ionic bond is formed as a result of the transference of electrons from one atom to another.

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Q2 :  

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


Answer :

Mg: There are two valence electrons in Mg atom. Hence, the Lewis dot symbol for Mg is:

Na: There is only one valence electron in an atom of sodium. Hence, the Lewis dot structure is:

B: There are 3 valence electrons in Boron atom. Hence, the Lewis dot structure is:

O: There are six valence electrons in an atom of oxygen. Hence, the Lewis dot structure is:

N: There are five valence electrons in an atom of nitrogen. Hence, the Lewis dot structure is:

Br: There are seven valence electrons in bromine. Hence, the Lewis dot structure is:

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Q3 :  

Write Lewis symbols for the following atoms and ions:

S and S2-; Al and Al3+; H and H-


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Q4 :  

Draw the Lewis structures for the following molecules and ions:

H2S, SiCl4, BeF2,, HCOOH


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Q5 :  

Define octet rule. Write its significance and limitations.


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Q6 :  

Write the favourable factors for the formation of ionic bond.


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Q7 :  

Discuss the shape of the following molecules using the VSEPR model:

BeCl2, BCl3, SiCl4, AsF5, H2S, PH3


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Q8 :  

Although geometries of NH3and H2O molecules are distorted tetrahedral, bond angle in water is less than that of ammonia. Discuss.


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Q9 :  

How do you express the bond strength in terms of bond order?


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Q10 :  

Define the bond length.


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Q11 :  

Explain the important aspects of resonance with reference to the ion.


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Q12 :  

H3PO3can be represented by structures 1 and 2 shown below. Can these two structures be taken as the canonical forms of the resonance hybrid representing H3PO3? If not, give reasons for the same.


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Q13 :  

Write the resonance structures for SO3, NO2 and.


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Q14 :  

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.


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Q15 :  

Although both CO2and H2O are triatomic molecules, the shape of H2O molecule is bent while that of CO2is linear. Explain this on the basis of dipole moment.


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Q16 :  

Write the significance/applications of dipole moment.


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Q17 :  

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


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Q18 :  

Explain with the help of suitable example polar covalent bond.


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Q19 :  

Arrange the bonds in order of increasing ionic character in the molecules: LiF, K2O, N2, SO2and ClF3.


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Q20 :  

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.


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Q21 :  

Apart from tetrahedral geometry, another possible geometry for CH4is square planar with the four H atoms at the corners of the square and the C atom at its centre. Explain why CH4is not square planar?


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Q22 :  

Explain why BeH2molecule has a zero dipole moment although the Be-H bonds are polar.


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Q23 :  

Which out of NH3and NF3has higher dipole moment and why?


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Q24 :  

What is meant by hybridisation of atomic orbitals? Describe the shapes of sp, sp2, sp3hybrid orbitals.


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Q25 :  

Describe the change in hybridisation (if any) of the Al atom in the followingreaction.


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Q26 :  

Is there any change in the hybridisation of B and N atoms as a result of the following reaction?

BF3+ NH3 F3B.NH3


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Q27 :  

Draw diagrams showing the formation of a double bond and a triple bond between carbon atoms in C2H4and C2H2molecules.


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Q28 :  

What is the total number of sigma and pi bonds in the following molecules?

(a) C2H2(b) C2H4


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Q29 :  

Considering x-axis as the internuclear axis which out of the following will notform a sigma bond and why? (a) 1s and 1s (b) 1s and 2px(c) 2pyand 2py(d) 1s and 2s.


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Q30 :  

Which hybrid orbitals are used by carbon atoms in the following molecules?

CH3-CH3; (b) CH3-CH=CH2; (c) CH3-CH2-OH; (d) CH3-CHO (e) CH3COOH


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Q31 :  

What do you understand by bond pairs and lone pairs of electrons? Illustrate by giving one example of each type.


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Q32 :  

Distinguish between a sigma and a pi bond.


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Q33 :  

Explain the formation of H2molecule on the basis of valence bond theory.


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Q34 :  

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


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Q35 :  

Use molecular orbital theory to explain why the Be2molecule does not exist.


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Q36 :  

Compare the relative stability of the following species and indicate theirmagnetic properties;

O2,,(superoxide), (peroxide)


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Q37 :  

Write the significance of a plus and a minus sign shown in representing the orbitals.


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Q38 :  

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


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Q39 :  

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


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Q40 :  

What is meant by the term bond order? Calculate the bond order of: N2, O2, and.


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<< Previous Chapter 3 : Classification of Elements and Periodicity in Properties Next Chapter 5 : States of Matter >>

Chemistry Part-1 - Chemistry : CBSE NCERT Exercise Solutions for Class 11th for Chemical Bonding and Molecular Structure will be available online in PDF book form soon. The solutions are absolutely Free. Soon you will be able to download the solutions.

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