chemistry

S.S.C CLASS 10^TH Q&A

CHEMICAL BOND

PART - A

SECTION - I

1. (a) Draw the shape of PCl5 molecule?

(a) Phosphorus Penta Chloride (PCl5):

1) In the vapour state PCl5 molecule has a "trigonal bi-pyramid" structure.

2) Three chlorines and phosphorus lie in one plane.

3) One chlorine above the plane and one chlorine below the plane are present.

(b) Draw the shape of ammonia molecule?

(b) Ammonia molecule (NH3):

1) Ammonia has a "pyramidal" shape.

2) The three hydrogens in one plane and nitrogen above the plane, as shown in

the figure.

3) Nitrogen has one lone pair of electrons in ammonia.

2. Why sigma bond is stronger than pi-bond?

2.A The strength of the bond depends on extent of overlap. The extent of overlap is

maximum in sigma bond and minimum in pi-bond. Hence sigma bond is stronger  than pi-bond.

3. Distinguish between sigma bond and pi-bond?

Sigma Bond Pi - Bond

1 The bond formed by the The bond formed by the

end-on-end overlap of side-on-overlap of orbitals of

orbitals of atoms is called atoms is called pi-bond.

sigma bond.

2 It has independent existence. It has no independent

existence.

3 It is the strongest bond. It is the weakest bond.

4 It is formed by the over- It is formed by the overlapping

lapping of of

i) s–s ii) s–p and i) p–p and ii) p-d orbitals.

4. Draw the bond formation of H2 molecule?

4.A Bond Formation of H2 Molecule:

Consider two hydrogen atoms having one unpaired electron, approaching each other.

Each atom has one unpaired electron in '1s' orbital. As these two atoms approach

each other, 's' orbital gets overlap at the internuclear distance as shown in the figure

and thus a hydrogen molecule is formed due to 's–s' overlap.

5. Explain the formation of sigma and pi-bonds duly showing orbital overlapping?

5.A (a) Sigma Bond:

(1) A strong bond formed by end-on-end overlap of two orbitals is called a "sigmabond".

(2) In this type of bond, maximum overlap of orbitals takes place and therefore the

bond formed is strong.

(3) Sigma bond can exist independently.

Eg: Molecules having ó bonds are H2, HCl, Cl2 etc.,

(4) Sigma bond is formed by

(i) s–s overlap

(ii) s–p overlap and

(iii) p–p overlap.

(i) s–s overlap :

(ii) p–p overlap :

(iii) s–p overlap :

(b) Pi-Bond:

1) A weak-bond formed by lateral overlap of two orbitals is called a pi-bond.

2) The extent of overlap is much less than in ó-bond.

3) It always exists along with a ó-bond.

4) It can not exist independently.

Eg: Molecules having ð-bond are C2H4, CO2, N4O2 etc.,

6. Draw the shapes of the molecules.

(1) water (H2O) (2) PCl3

6.A 1. Water Molecule:

(1) Water molecule is non-linear and has "V"-shape.

(2) In water molecule, two lone pairs of electrons are present on oxygen atom.

2. PCl3 molecule:

(1) PCl3 has "pyramidal shape".

(2) Three chlorines are in one plane and phosphorus lies above the plane.

(3) Phosphorus has one lone-pair of electrons in PCl5.

7. Explain the formation of NH+

4 ion?

7.A Formation of NH4

+ ion:

(1) In NH3, a lone pair of electrons are available on Nitrogen [:NH3]

(2) In H+ ion, the '1s' orbital is empty.

(3) In ammonia (:NH3), nitrogen contributes a pair of electrons for bond formation with

H+.

(4) This results in the formation of co-ordinate covalent bond.

H+ + :NH3 → [H : NH3]+ (or) H ← :NH3

8. Draw the bond formation of HCl molecule?

8.A Formation of HCl molecule:

(1) Consider the formation of HCl molecule.

(2) Hydrogen atom has an unpaired electron is '1s' orbital and chlorine atom has an

unpaired electron in 2pz orbital.

(3) As the two atoms approach each other overlap takes place between 's' and 'p'

orbitals.

(4) Thus HCl molecule is formed by s-p overlap.

SECTION - II

Very Short Answers

1. Draw the shape of water molecule?

1.A 1) Water molecule has 'V'-shape.

2) Oxygen has two lone pair electrons in H2O molecule.

2. Name the two molecules having pyramidal shape?

2.A Molecules having pyramidal shape are

i) ammonia (NH3)

ii) phosphorus trichloride (PCl3)

iii) phosphine (PH3)

3. What is the shape of ammonia molecule? Draw it and explain?

3.A Ammonia molecule:

1) NH3 molecule has a pyramidal structure.

2) Three Hydrogens in one plane and nitrogen is above the plane.

3) Nitrogen has one lone pair of electrons in ammonia.

4. Give three examples of molecules having a double bond?

4.A Molecules having a double bond are

i) ethylene (C2H4)

5. Give two examples of molecules having a triple bond?

5.A Molecules having a triple bond are

i) acetylene (C2H2)

ii) Nitrogen (N2)

iii) Calcium Carbide (Ca C2)

iv) Hydrogen Cyanide (HCN)

6. Name two molecules having p-p overlapping?

6.A Molecules having p–p overlap are

(1) Bromine (Br2)

(2) Chlorine (Cl2)

(3) Fluorine (F2)

(4) Oxygen (O2)

7. Which orbitals can form pi (ð) bond?

7.A 'p' and 'd' orbitals can form pi-bonds.

8. What is the shape of carbon dioxide molecule?

8.A The shape of carbon-di-oxide molecule is linear.

9. Show the electron dot structure of H2 molecule?

9.A The electron dot structure of H2 molecule is

10. What are multiple covalent bonds? Give examples?

10.A "Molecules having double and triple covalent bonds are" called as "multiple covalent

bonds".

Eg: 1) Nitrogen molecule (N≡N)

2) Oxygen molecule (O=O)

3) Hydrogen cyanide molecule (H–C≡N)

SECTION - III

Long Answer Questions (4 Marks Each)

1. Explain the formation of a double-bond with example?

1.A Double Bond:

"The bond formed by sharing of two pairs of electrons between two atoms" is called

a "double bond".

Eg: O2, CO2, C2H4, etc.,

Formation of Double bond in oxygen molecule:

(1) Consider the formation of oxygen molecule (O2)

(2) The electronic configuration of oxygen is 1s2 2s2 2p4 ie.

(3) Oxygen has two unpaired electrons one each in 2py and 2pz orbitals.

(4) The 2pz orbital of one oxygen atom overlap with the '2pz' orbital of another oxygen by

end-on-end overlap resulting in the formation of a 'ó' bond.

(5) Two '2py' orbitals of two oxygen atoms are parallel to each other, and perpendicular

to 2pz. So '2py' orbitals overlap side-ways and form a 'ð'-bond.

(6) Thus oxygen molecule is formed by one sigma bond and one pi-bond and having a

double bond.

1s2 2s2 2px

2 2py

1 2pz

1

2. Explain the formation of co-ordinate covalent bond?

2.A Co-ordinate Covalent Bond:

A chemical bond formed by the sharing of an electron pair, contributed by one of the

two combining atoms is called "co-ordinate covalent bond".

Eg: NH3 BF3, NH+

4, H3O+ etc.,

Formation of Ammonia-Boron Trifluoride molecule:

(1) Ammonia molecule has pyramidal shape and has a lone pair of electrons on nitrogen.

(2) Boron Trifluoride (BF3) molecule has an empty orbital.

(3) NH3 molecule donates an electron pair to BF3 and forms a "co-ordinate covalent

bond".

(4) Co-ordinate covalent bond is designate as "→" from donor to acceptor.

(5) Nitrogen donates its lone pair of electrons and Boron accepts. Thus Ammonia Boron

Tri-fluoride molecule is formed by the formation of a "co-ordinate covalent bond".

3. Explain s–p overlap with examples?

3.A s–p overlap:

"The overlap of 's' orbital of one atom and 'p' orbital of another atom" is called "s–p

overlap".

Eg: HCl, HF, HBr

Formation of HCl molecule:

(1) Consider the formation of HCl molecule.

(2) The electronic configuration of hydrogen is '1s' and the the electronic configuration of

chlorine is 1s2 2s2 2p5 3s2 3p5

Hydrogen : 1s1

Chlorine : 1s2 2s2 2p6 3s2 3p5

(3) Hydrogen atom has one unpaired electron in '1s' orbital and chlorine has one

unpaired electron in '3pz' orbital.

(4) When the two atoms approach other, overlap takes place between s and p orbitals at

↑

F3BO + : NH3 → F3B ← NH3

inter nuclear distance.

(5) Thus HCl molecules is formed due to s–p overlap.

4. Explain the formation of triple bond in Nitrogen molecule?

                                        (or)

Explain the formation of multiple bond with an example?

4.A Triple Bond:

"The bond formed by sharing of three pairs of electrons between two atoms", is called

"Triple covalent bond".

Eg: N2, C2H2, HCN etc.,

Formation of a Triple Bond in Nitrogen Molecule:

(1) The electronic configuration of nitrogen is N = 7 = 1s2 2s2 2p3 =

(2) There are three unpaired electrons, one each in 2px, 2py, 2pz orbitals.

(3) The two 2pz orbitals of two nitrogen atoms overlap end-on-end to form a sigma (ó)

bond.

(4) The remaining two orbitals 2py and 2pz are perpendicular to each other, hence these

orbitals overlap sideways to give rise to two ð-bonds.

(5) Thus, in nitrogen a triple bond is formed.

(6) In nitrogen molecule, one sigma bond and two pi bonds are present.

5. Discuss the type of overlaps that are possible with s and p orbitals?

5.A Overlapping with 's' and 'p' orbitals:

Three types of overlaps are possible with 's' and 'p' orbitals. They are

(i) s–s overlap

(ii) p–p overlap

(iii) s–p overlap

(i) s–s overlap: The overlap of 's' orbitals of two atoms is called 's–s' overlap.

Eg: H2

1s2 2s2 2px

1 2py

1 2pz

1

Formation of H2 molecule:

(1) Consider two hydrogen atoms having one unpaired electron each in '1s' orbital.

(2) As two hydrogen atoms approach each other, '1s' orbitals of two atoms overlap by

end-on-end manner and forms a sigma bond.

(ii) p–p overlap: The overlap of 'p' orbitals of two atoms is called "p–p overlap".

Eg: F2, Cl2, Br2...

Formation of F2 molecule:

(1) The electronic configuration of fluorine atom is F = 9 =

(2) Fluorine atom has one unpaired electron in '2pz' orbital.

(3) So, when two fluorine atoms approach each other. Their 2pz orbitals overlap by endon-

end manner and forms a sigma bond.

(iii) s–p overlap: "The overlap of 's' orbital of one atom and 'p' orbital of another atom" is

called "s–p" overlap.

Eg: HCl, HF, HBr

Formation of HCl molecule:

(1) The electronic configuration of hydrogen and chlorine are 1s1 and 1s2 2s2 2p6 3s2 3p5

respectively.

(2) Hydrogen = 1s1

Chlorine = 1s2 2s2 2p6 3s2 3px

2 3py

2 3pz

1

1s2 2s2 2px

2 2py

2 2pz

1

(3) Hydrogen has one unpaired electron in '1s' orbital and chlorine has one unpaired

electron in '3pz' orbital.

(4) When these two atoms approach each other, their 1s and 3pz orbitals overlap by endon-

end manner and forms a sigma bond.

PART - B

I. Multiple Choice Questions (1/2 Mark Each)

1. Shape of CO2 is

A) V-shape

B) Pyramidal

C) Linear

D) Tetrahedral

2. End-on-End overlap results in

A) pi-bond

B) sigma bond

C) hydrogen bond

D) ionic bond

3. The number of valency electrons in carbon atom.

A) 0

B) 2

C) 4

D) 6

4. The octet rule is not valid for the molecule

A) CO2

B) SO2

C) H2O

D) O2

5. "V" shaped molecule is

A) PCl3

B) H2O

C) PCl5

D) NH3

6. s–p overlap is present in

A) H2

B) Cl2

C) O2

D) HCl

7. An element has the electronic configuration is

1s2 2s2 2p6 3s2 3p2. Its valence electrons are

A) 2

B) 6

C) 3

D) 4

8. Co-ordinate covalent bond is present in

A) HCl

B) H2O

C) H3O+

D) H2

9. A triple bond has

A) one ó, two ð bonds

B) one ð, two ó bonds

C) three ó bonds

D) three ð bonds

10. The shape of Boron Trifluoride molecule is

A) Planar triangular

B) Linear

C) Trigonal bi-pyramidal

D) Tetrahedral

11. In ammonia Boron trifluoride, the donor is

A) Boron

B) N and B

C) N

D) None

12. The no.of ó and ð bonds in CO2

A) 1 and 2

B) 2 and 1

C) 2 and 2

D) 3 and 3

13. Bond angle in water molecule is

A) 109°28'

B) 120°

C) 180°

D) 105°

14. Molecule having single bond is

A) O2

B) N2

C) CO2

D) HCl

15. The type of bond present in ethylene is

A) single bond

B) double bond

C) triple bond

D) ionic bond

II. Fill in the blanks (1/2 Mark Each)

16. The shape of ammonia molecule is ______

17. The shape of PCl5 molecule is ______

18. The bond angle in H2O molecule is ______

19. The strength of bond depends on ______

20. The bond in HCN is ______

21. The chemical formula of hydronium ion is ______

22. Sigma bond is formed by ______ overlap of orbitals.

23. Covalent bond was suggested by ______

24. The filling of valence orbital with 8 electrons is called ______

25. The bond present in NH+

4 molecule is ______

26. ______ bond is formed by maximum overlap of orbitals.

27. In co-ordinate covalent bond, both the electrons are supplied by ______

28. The bond that can not exist independently is ______

29. The shape of acetylene molecule is ______

30. The shape of PCl3 molecule is ______

III. Match the following (1/2 Mark Each)

I. Group - A Group - B

31. s–s overlap ( ) A) O2

32. s–p overlap ( ) B) H2

33. p–p overlap ( ) C) NH4

+

34. double bond ( ) D) HCl

35. Co-ordinate covalent ( ) E) Cl2

II. Group - A Group - B

36. Linear ( ) A) Kossel

37. Pyramidal ( ) B) PCl5

38. Trigonal pyramidal ( ) C) H2O

39. Ionic bond ( ) D) CO2

40. 'V'-shape ( ) E) PH3

KEY

PART - B

I.

1. C 2. B 3. C 4. B 5. B 6. D 7. D 8. C

9. A 10. A 11. C 12. C 13. D 14. D 15. B

II.

16. Pyramidal 17. Trigonal bi-pyramidal 18. 105°

19. maximum extent of overlapping 20. Triple bond

21. H3O+ 22. end-on-end

23. Lewis 24. octet configuration

25. co-ordinate covalent bond 26. sigma bond 27. donor

28. pi-bond 29. Linear 30. pyramidal

III.I

31. B 32. D 33. E 34. A 35. C

IV

36. D 37. E 38. B 39. A 40. C