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Chemical Bonding and Molecular Structure

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Chemistry Part I

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Chemistry

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Class 10 Class 12

During the change of O2 to O2- ion, the electron adds on which one of the following orbitals?

  • π* orbital

  • π orbital

  • σ* orbital

  • σ orbital


A.

π* orbital

During the change of O2 to O2-the electron adds on π* orbital. Molecular orbital configuration of O2 (total e- =16)
 straight sigma 1 straight s squared comma space straight sigma asterisk times 1 straight s squared comma space straight sigma 2 straight s squared comma straight sigma asterisk times 2 straight s squared comma straight sigma 2 straight p subscript straight z superscript 2 comma space straight pi 2 straight p subscript straight x superscript 2 almost equal to straight pi 2 straight p subscript straight y superscript 2 space comma space straight pi asterisk times 2 straight p subscript straight x superscript 1 almost equal to straight pi asterisk times 2 straight p subscript straight y superscript 1

and space configuration space of space straight O subscript 2 superscript minus space left parenthesis 8 plus 8 plus 1 space equals space 17 right parenthesis
straight sigma 1 straight s squared comma space straight sigma asterisk times 1 straight s squared comma space straight sigma 2 straight s squared comma straight sigma asterisk times 2 straight s squared comma straight sigma 2 straight p subscript straight z superscript 2 comma space straight pi 2 straight p subscript straight x superscript 2 almost equal to straight pi 2 straight p subscript straight y superscript 2 space comma space straight pi asterisk times 2 straight p subscript straight x superscript 2 almost equal to straight pi asterisk times 2 straight p subscript straight y superscript 1

During the change of O2 to O2-the electron adds on π* orbital. Molecular orbital configuration of O2 (total e- =16)
 straight sigma 1 straight s squared comma space straight sigma asterisk times 1 straight s squared comma space straight sigma 2 straight s squared comma straight sigma asterisk times 2 straight s squared comma straight sigma 2 straight p subscript straight z superscript 2 comma space straight pi 2 straight p subscript straight x superscript 2 almost equal to straight pi 2 straight p subscript straight y superscript 2 space comma space straight pi asterisk times 2 straight p subscript straight x superscript 1 almost equal to straight pi asterisk times 2 straight p subscript straight y superscript 1

and space configuration space of space straight O subscript 2 superscript minus space left parenthesis 8 plus 8 plus 1 space equals space 17 right parenthesis
straight sigma 1 straight s squared comma space straight sigma asterisk times 1 straight s squared comma space straight sigma 2 straight s squared comma straight sigma asterisk times 2 straight s squared comma straight sigma 2 straight p subscript straight z superscript 2 comma space straight pi 2 straight p subscript straight x superscript 2 almost equal to straight pi 2 straight p subscript straight y superscript 2 space comma space straight pi asterisk times 2 straight p subscript straight x superscript 2 almost equal to straight pi asterisk times 2 straight p subscript straight y superscript 1


Which one of the following pairs is isostructural (i.e., having the same shape and hybridization)?

  • [BCl3 and BrCl3]

  • [NH3 and NO3-]

  • [NF3 and BF3]

  • [BF-4 and NH4-]


D.

[BF-4 and NH4-]

If a number of bond pairs and lone pairs are same for the given pairs, they are isostructural.



If a number of bond pairs and lone pairs are same for the given pairs, they are isostructural.




The enolic form of ethyl acetoacetate as below has

  • 18 sigma bonds and 2 pi-bond

  • 16 sigma bonds and 1 pi-bond

  • 9 sigma bonds and 2 pi-bond

  • 9 sigma bonds and 1 pi-bond


A.

18 sigma bonds and 2 pi-bond

In enolic form of ethyl acetoacetate has 16 single bonds i.e 16 sigma bond and 2 double bonds i.e 2 sigma bonds and 2pi bonds.
Hence, the given structure has 18 sigma bonds and 2 pi bonds.

In enolic form of ethyl acetoacetate has 16 single bonds i.e 16 sigma bond and 2 double bonds i.e 2 sigma bonds and 2pi bonds.
Hence, the given structure has 18 sigma bonds and 2 pi bonds.


Consider the following compounds

Hyperconjugation occurs in 

  • I only

  • II only

  • III only

  • I and III


C.

III only

Hyperconjugation occurs through the H- atoms present on the carbon atom next to the double bond i.e alpha hydrogen atoms. There is no alpha -H in the structure I and II.
So, hyperconjugation occurs in structure III only ie. 

Hyperconjugation occurs through the H- atoms present on the carbon atom next to the double bond i.e alpha hydrogen atoms. There is no alpha -H in the structure I and II.
So, hyperconjugation occurs in structure III only ie. 


Consider the molecules CH4, NH3 and H2O. Which of the given statement is false?

  • The H-O-H bond angle in H2O  is larger than the H-C-H bond angle in CH4.

  • The H-O-H bond angle in H2O is smaller than the H-N-H bond angle in NH3.

  • The H-C-H bond angle in CH4 is larger than the H-N-H bond angle in NH3

  • The H-C-H bond angle in CH4, the H-N-H bond angle in H2O are all greater than 900.


A.

The H-O-H bond angle in H2O  is larger than the H-C-H bond angle in CH4.

According to VBT: lone pair-lone pair repulsion is more than a bond pair -lone pair repulsion.
As the number of lone pair of electrons on central element increases, repulsion between that lone pair of electrons increases and therefore, bond angle decreases.

Molecules

Bond angle

CH4 (no lone pair of electrons)

1090.5

NH3(one lone pair of electrons)

107.50

H2O (two lone pair of electrons)

104.450

According to VBT: lone pair-lone pair repulsion is more than a bond pair -lone pair repulsion.
As the number of lone pair of electrons on central element increases, repulsion between that lone pair of electrons increases and therefore, bond angle decreases.

Molecules

Bond angle

CH4 (no lone pair of electrons)

1090.5

NH3(one lone pair of electrons)

107.50

H2O (two lone pair of electrons)

104.450