Chemical Bonding and Shape of Molecules

                                   Questions  and Answers

1. How would you confirm that B in BF₃ gets sp² Hybridization?

> The central atom Boron has one half filled orbital in ground state (1_s¹2_s²2px¹2py⁰2pz⁰) but it has          three half filled orbital in excited state since one electron is promoted from 2s to 2p orbital during chemical combination.

      Hence, one 2s and two 2p orbital undergo sp² hybridization to form three Sp² hybrid orbital of equivalent energy and identical shape & size which takes trigonal planer geometry with bond angle 120⁰.

 

 

Each half filled sp² hybrid orbital of boron overlaps with half filled 2p_z orbital of three fluorine atom to form three covalent bonds.

2. C in C₂H₂ gets sp hybridization, why?

>Each carbon has two half filled orbitals in ground state (1s²2s²2p_×12p­_y¹2p_z⁰).It has four unpaired        electrons in excited state one electron is promoted from 2s to empty 2p orbital during chemical   reaction                                          (1s²2s¹2p_x¹2p_y¹2p_z¹). One 2s and one 2p orbitals undergoes sp hybridization to form two sp hybrid orbitals of equivalent energy and identical shape which has linear geometry and bond angle 180⁰.

One half filled sp hybrid orbital of carbon atom overlaps with another half filled sp hybrid orbital to form sigma bond. The remaining half filled Sp hybrid orbital of each carbon atoms overlaps with half     filled orbitals hydrogen to form sigma bond. The unhybridized orbital of carbon atoms pi bond.

 

 

 3. State any two proper conditions for hybridization. What is the mode of hybridization of C in C₂H₂?

>The necessary condition for hybridization:

1. The orbitals taking part in hybridization must have only small difference of enthalpies.

2. The orbital undergoes hybridization generally belong to the valence of the atom. The mode of hybridization of  C in C₂H₂ is sp-hybridization.

 

4. Predict the mode of hybridization of B in BF₃. Mention any two features of this hybridization.

->The central atom B in BF₃ has Sp² hybridization. Two important features of this hybridization are:

1. Bond angle of Sp² hybrid orbital is 120⁰.

2. Sp² hybrid orbital having 33% s-character and 66% p-character.

 

5. Predict the model of hybridization. i)Carbon in ethane  ii)oxygen in water

> i) The hybridization of carbon in ethyne is p-hybridization.

    ii) The hybridization of oxygen in water is sp³-hybridization.

 

6. Write two important features of hybrid orbitals.

> The two important features of hyhbrid orbitals are;

  i) They have same shape and same energy.

 ii) They are equivalent and symmetrical.

 

7. Which kind of hybridization result into tetrahedral geometry? Give an example of such hybridization.

-> sp³ hybridization results into tetrahedral geometry.

Example: methane (CH₄)

 8. Which kinds of hybridization results into linear geometry. Give an example of such hybridization.

> sp hybridization results into linear geometry.

Example: - Ethyne (C₂H₂) has sp hybridization.

 9. What kind of hybridization result into trigonal planar geometry. Give an example of it.

> Sp² hybridization results into trigonal planer geometry. Example: ethene (CH₂=CH₂).

 10. How would you predict the geometry of ammonia molecules on the basis of VSEPR theory?

> According to VSEPR model, molecules takes a shape that minimizes the repulsion between bonding pair i.e. bond pair and non-bonding i.e. lone pair of electron.

Lone pair-bond pair i.e. bond pair repulsion>bond pair-bond pair repulsion

In NH₃ molecule, three bonding pair of electron and one lone pair of electron are present. Due to the presence of lone pair of electron the regular tetrahedral structure of NH₃ is distorted to give triangular pyramidal shape and having bond angle 106⁰45'. This gives the maximum stability between the bond pair and lone pair of electrons.

 

 

 

 11. Ammonia molecules has got trigonal pyramidal geometry even though though nitrogen of ammonia gets Sp³ hybridization. Give reason.

> The central atom N has one lone pair and three bonding electrons. Three bonding electrons are           shared with three hydrogen atom to form three bond pair electrons. According to VSEPR theory, lone pair-bond pair electros. According to VSEPR theory, lone pair-bond pair repulsion is greater than bond pair-bond pair repulsion. Due to the unequal repulsion, tetrahedral geometry is distorted       

and changed into trigonal pyramidal geometry.

 

12. Predict the mode of hybridization in the central atom of the molecules having  

 (i) trigonal planner (ii) tetrahedral structure with an example of each.

>i) Trigonal planner: The mode of hybridization in certain atom is sp². Example: BF₃

   ii) Tetrahedral: The mode of hybridization in centre atom is Sp³.

           Example:- CH₄

 

13. Define hybridization and write any two features of tetrahedral hybridization.

 > The process of mixing of dissimilar atomic orbital of same atom giving rise to equal number of new set of orbital having same energy is known as hybridization.

Features of tetrahedral hybridization.

Two important features of tetrahedral hybridization are:

a. Carbon atoms are sp³ hybridization.

b. The bond angles are 109.5°.

 

14. what are the features of. Tetrahedral hybridization? Write an exam of it.

 > Following are the features of tetrahedral hybridization.

a. Carbon atoms are sp³ -hybridiszation.

b. The bond as angles are 109.5°.

  Example: Methane (CH₄), the central carbon atom is sp³ hybridization.

 

15. state the mode of hybridization in B of BF₃ and C of C₂H₆.

> The mode of hybridization in B of BF₃ is sp² hybridization and mode of hybridization in C of C₂H₆ is   sp³.

 

16.Which kind of hybridization results into tetrahedral geometry? Mention any one character of such hybridization.

> Sp³ hybridization have tetrahedral geometry. sp³ hybridization is formed by mixing of one s-orbital and three p-orbital. The characteristics of sp³ hybrid orbital: it has bond angle 109.5° and tetrahedral shape.

 

17.Which kind of hybridization results into tetrahedral geometry? Mention any one character of such hybridization.

> The mode of hybridization in carbon of acetylene is sp.

  Two important features of sp-hybridization are:

i. The bond angle are 180°.

ii. The space sp-hybridization is linear, sp hybridization orbital possess 50% s-character and 50% s-character and 50% p-character.

 

18. Predict the geometry of molecules having:

     a. sp³ hybridization

     b. so hybridization with am example of each.

 > a. sp³ hybridization:- The molecules having sp³ hybridization generally possess tetrahedral shape. Example:- CH₄ molecule.

  b. so hybridization:- The molecules having sp hybridization generally possess linear shape.

Example:- CH₂H₄ molecule.

 

19.write any two features of sp³ hybrid orbital with an example.

> Two features of sp³ hybrid orbital are:

i. The bond angle of sp³ hybrid orbital is 109.5° and tetrahedral shape.

II. sp³ hybridization orbital possesses 25% s-character and 75% p-character.

Methane molecules has sp³ hybrid orbital.

 

20.what is meant by hybrid orbital? Write an example of it.

> Hybrid orbital:- The process of mixing of dissimilar atomic orbitals of same atom giving hybridization and new orbital is called hybrid orbital.

Example:- Mixing of one s-orbital with one p-orbital to give two sp-hybrid orbital.

 

21.Why do NH₃ and BF₃ have dissimilar geometries?

>In NH₃ molecule, the centaral atom N has one lone pair and three bonding electrons. These three bonding electrons is shared by three hydrogen atom to form three bonding pair of electrons. But in the case of BF₃ molecule, central atom do not have lone pair electron and only form three covalent with three F atom. Due to the lone pair and bond pair repulsion, geometry of NH₃ and BF₃ are different.

22.State the mode of hybridization of C₂H_5­ and mention any two features of this hybridization.

>Ethane molecule i.e. C₂H₆ has sp3 hybridization. Two features of sp³-hybridization are:

   i. The bond angle of sp3 hybrid orbital is 109.5 degree and tetrahedral shape.

   ii. sp3 hybridized orbital posses 25% s-character and 75% p-character.

 23. Write any important characters of tetrahedral hydridization.

 Following are two important characters :

     i. Carbon atoms are sp3-hybridization.

      ii. The bond angle are 109.5 degree.

24.  Mention one example of each:

    i. In methane (CH₄), the central carbon atom is sp3-hybridizaton I.e. tetrahedral shape.

   ii. In boron trifluoride (BF₃), the central boron atom has trigonal hybridization.

25.What is the mode of hybridization of the central atom whose molecular geometry is tetrahedral? And give an example of its.

>If the molecule has molecular geometry of tetrahedral, the central atom of the molecule is sp³ hybridization.

Examples : In CH4 molecule, the central carbon atoms are insp³ hybridization and having bond angle 109.5 degree.

 

26. predict the mode of hybridization in

   i. C of C₂H₄                        ii. B of BF³

  >   I. the mode of hybridization is C of CH₂H₄ is also SP2 hybridization.

      Ii. The mode of hybridization in B of BF3 is also SP2 hybridization.

 

27. Why is H-O-H bond angle in water molecules comparatively higher than H-S-H bond angle in H₂S molecule?

> In both molecules i.e. H₂O and H₂S, the central atom O- and S- are SP₃ hybridized orbital and both two having two bond pair and two lone pair of electros .  O- atom has similar size and higher electronegativity than S- atom, due to this reason bond pair in H₂O are closer to the oxygen  atom and repulsion between them are large. In the case of H₂S , the bond pair are away from the central atom. The bond angle in water molecule is comparatively higher than H₂S.

28. Define hybridization. Draw the orbital picture of a hydrocarbon showing tetrahedral structure.

> The process of mixing of dissimilar atomic orbitals of same atom giving, rise to equal number of a new set of orbitals having same energy is known as hybridization. Methane shows tetrahedral structure and orbital picture of methane is

   

 29. How do you predict the molecular geometry of NH₃ based on VESPR model ?

>  According to VSEPR model, a molecule takes a shape that minimizes the repulsion between bonding pair i.e. bond pair and non-bond pair of electron.[ Lone pair-bond repulsion> bond pair-bond pair repulsion] In NH₃ molecule, three bonding pair of electrons and one lone pair of electrons are present. Due to the presence of lone pair of electrons the regular tetrahedral structure of NH₃ is distorted to give triangular pyramidal shape and having bond angle 106degree 45min. This gives the maximum stability between the bond pair and lone pair of electrons.  

 

30. The bond angle at the central atom in NF₃ is 103degree, whereas in BF₃ is 120degre, what factor accounts for the difference in bond angles?

> Due to the presence of lone pair of electrons in central atom N in NF₃, the lone pair-bond pair repulsion is greater than bond pair repulsion. The shape of NF₃ is pyramidal trigonal geometry. Due to the absence of lone pair of electron B in BF₃, there is only bond pair-bond pair repulsion and having triangular geometry with bond angle 120 degree. Therefore, NF₃ has pyramidal trigonal and BF₃ has triangular geometry.

31. How would you interpret that all four C-H bonds of methane are identical ?

> All the four carbon atoms in methane are sp³ hybridization which are directed towards the four corners of regulars tetrahedral having bond angle of 109.5 degree. Each bond is formed by the head overlapping at sp³ shybrid orbital of carbon and S-orbital of hydrogen. Therefore, all the four C-H bond methane are identical. 

32. Draw the molecular orbital picture of ethane.

> Molecular orbital picture of ethene is given below:

    

33.Draw the orbital picture of ethyne indicating sigma and pi bonds.

> Orbital picture of ethyne indicating sigma and pi-bonds is given below:

34.Draw the shape of sp and sp² hybrid orbitals.

> when one S-orbital and one p-orbital are mixed together then  two sp-hybrid orbital is formed. The shape of sp-hybrid orbital is linear .i.e. bond angle 180 degree.

> when  one s-orbital and two p-orbital are mixed together then three sp2- hybrid orbital is formed. The shape of sp2-hybrid orbital is trigonal i.e. bond angle 120 degree

35.  Identify the hybridization of the indicator atom in each of the following molecules. 

A   Be in BeF₂        b. B in BF₃    c. N in NH

>     Hybridization of Be in BeF₂ is sp-hybridization.

        Hybridization of B in Bf₃ is sp² hybridization. 

        Hybridization of N in NH₃ is sp³ hybridization.

36. Predict the structure of methane based on hubridization.

>   The electronic configuration of central atmo C in methane is

        C6=1s²2s²2p²(ground state)

 The P-orbital is empty. During bond formation, carbon atom absorbs energy and one 2s
electron gets promoted to 2p orbital.

C6=1s²2s¹2p³(excited state)

These four sp³ hybrid orbital overlap with 1s orbital of 4 hydrogen atoms to give a methane molecule. Thrse four bondsare directed towards the corners of a regular tetrahedral with bond angle of 109.5°.

figure:-

37.  Explain the state of hybridization in ethyne molecule.

       >   The central carbon atom in ethyne and one p- orbital of the exicted carbon atom hybridize to form two sp hybrid orbital. Two sp hybrid orbital are inclined to each other at right angle i.e bond angle 180°. In ethyne, each carbon atom forms two sigma bond using sp hybrid orbital and two pi bonds are formed by using unused p orbitals of carbon atim. The orbital pictures of ethyne is

38. What do you understand by sp² hybridization ? Using any example explain the molecular geometry involved.

> sp²-hybridization: When one s-orbital and two p-orbital mix together to form three sp²-hybrid orbital, is called sp²-hybridization. The three hybrid orbitals are oriented to the three conrers of a triangle having an angle of 120° to one another.

 

 

 

          Ethene molecule has sp² hybridization. In ethene molecule the three sp2 hybrid orbitals form sigma bonds, while the unused p-orbital will form π bond. The orbital picture of ethene molecule is

39.    Using VSEPR theory, explain the shapes of BeF₂ and BF₂.  

  >  In BeF₂ molecule, the central atom Be have two valence electrons.  These two elections are shared by two F atoms and two bond pair of electrons are formed around the central atom Be. According to VSEPR theory, these two bond pair of electron are arranged in such a way that there must be maximum repulsion.  These two bond pair is in 180° apart from each other. The geometry of BeF₂ is linear.

In BF₃ molecule, the central atom B has three valence electrons. These three electrons are shared by three F atom to form three bond pair of electrons. They have equal force of repulsion among each other and are oriented in triangular geometry with bond angle 120°.

40. VSEPR model

> Valence shell electron pair repulsion theory is also called VSEPR theory. This theory was given by Sidgwick and Powell. This theory describes the influence of lone pair of electrons to the bonding electrons and also predicts the shape of molecule. This theory is based on the number of valence of electrons present in the central atom of a molecule.

Statement: "A molecules take a shape that minimizes the repulsion between the bonding and non-bonding pair of electrons".

Following are the postulates of VSEPR theory.

a. In any covalent molecule, there is a central atom around which other atoms are arranged.

b. The shape of molecule is determined by the number of electrons pair presents in the valence shell of the central atom.

 c. If the central atom of a molecules is surrounded by electron pairs of dissimilar atoms then the molecules will have irregular geometry due to different repulsive  interaction.

d. If the central atom in a molecule is surrounded by both lone pair and bond pair of electron then the molecules will have irregular geometry due to different repulsive interaction.

e. The order of repulsion between electron pair are ;

   Lone pair-lone pair>lone pair-bond pair