Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Tamilnadu State Board New Syllabus Samacheer Kalvi 9th Science Guide Pdf Chapter 13 Chemical Bonding Text Book Back Questions and Answers, Notes.

Samacheer Kalvi 9th Science Solutions Guide Chapter 13 Chemical Bonding

9th Science Guide Chemical Bonding Text Book Back Questions and Answers

I. Choose the correct answer:

Question 1.
Number of valence electrons in carbon is
(a) 2
(b) 4
(c) 3
(d) 5
Answer:
(b) 4

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 2.
Sodium having atomic number 11, is ready to ______________ electron/electrons to attain the nearest noble gas electronic configuration.
(a) gain one
(b) gain two
(c) lose one
(d) lose two
Answer:
(c) lose one

Question 3.
The element that would form anion by gaining electrons in a chemical reaction is ………………..
(a) potassium
(b) calcium
(e) fluorine
(d) iron
Answer:
(c) fluorine

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 4.
Bond formed between a metal and non metal atom is usually …………………..
(a) ionic bond
(b) covalent bond
(e) co-ordinate bond
Answer:
(a) ionic bond

Question 5.
______________ compounds have high melting and boiling points.
(a) Covalent
(b) Coordinate
(e) Ionic
Answer:
(c) Ionic

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 6.
Covalent bond is formed by …………………
(a) transfer of electrons
(b) sharing of electrons
(c) sharing a pair of electrons
Answer:
(b) sharing of electrons

Question 7.
Oxidising agents are also called as …………………. because they remove eletrons form other substances.
(a) electron donors
(b) electron acceptors
Answer:
(b) electron acceptors

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 8.
Elements with stable electronic configurations have eight electrons in their valence shell. They are ……………….
(a) halogens
(b) metals
(c) nobel gases
(d) non metals
Answer:
(c) noble gases

II. Answer briefly :

Question 1.
How do atoms attain Noble gas electronic configuration?
Answer:
Atoms can combine either by transfer of valence electrons from one atom to another or by sharing of valence electrons in order to achieve the stable noble gas electronic configuration.

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 2.
NaCl is insoluble in carbon tetrachloride but soluble in water. Give reason.
Answer:
NaCl is an ionic compound, it is soluble in polar solvent (water). Whereas CCl4 is a covalent compound. So.it is insoluble in polar solvent (water). But it is soluble in non¬polar solvents.

Question 3.
Explain Octet rule with an example.
Answer:
The tendency of atoms to have eight electrons in the valence shell is known as the ‘Octet rule’ or the ‘Rule of eight’ For example, Sodium with atomic number 11 will readily loose one electron to attain Neon’s stable electronic configuration. Similarly, chlorine has electronic configuration 2,8,7. To get the nearest noble gas (i.e. Argon) configuration, it needs one more electron. So chlorine readily gains one electron from other atom and obtains stable electronic configuration. Thus elements tend to have stable valence shell (eight electrons) either by losing or gaining electrons.
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 1
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 2

Question 4.
Write a note on different types on bonds.
Answer:
There are different types of chemical bonding possible between atoms which make the molecules. Depending on the type of bond they show different characteristics or properties.
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 3

Question 5.
Correct the wrong statements.
(a) Ionic compounds dissolve in non polar solvents.
(b) Covalent compounds conduct electricity in molten or solution state.
Answer:
(a) Covalent compounds dissolve in non-polar solvents. (or) Ionic compounds dissolve in polar solvents.
(b) Ionic compounds conducts electricity in molten or solution state.

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 6.
Complete the table give below.
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 4

Answer:

Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 5

Question 7.
Draw the electron distribution diagram for the formation of Carbon di oxide (CO2) molecule.
Answer:
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 6

Question 8.
Fill in the following table according to the type of bonds formed in the given molecule.
CaCl2, H2O, CaO, CO, KBr, HCl, CCl4, HF, CO2, Al2Cl6
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 7

Answer:

Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 8

Question 9.
The property which is characteristics of an Ionic compound is that
(a) it often exists as gas at room temperature.
(b) it is hard and brittle.
(c) it undergoes molecular reactions
(d) it has low melting point.
Answer:
(b) it is hard and brittle

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 10.
Identify the following reactions as oxidation or reduction.
(a) Na → Na+ + e
(b) Fe3+ + 2 e → Fe+
Answer:
(a) oxidation
(b) reduction

Question 11.
Identify the compounds as Ionic/Covalent/Coordinate based on the given characteristics.
(a) Soluble in non polar solvents
(b) Undergoes faster/instantaneous reactions
(c) Non conductors of electricity
(d) Solids at room temperature
Answer:
(a) Co-ordinate Covalent compound.
(b) Ionic compound.
(c) Covalent compound.
(d) Ionic compound.

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 12.
An atom X with atomic number 20 combines with atom Y with atomic number 8. Draw the dot structure for the formation of the molecule XY
Answer:
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 9

Question 13.
Considering MgCl2 as ionic compound and CH4 as covalent compound give any two differences between these two compounds.
Answer:

MgCl (ionic compound) CH4(covalent compound)
1. It is formed by the transfer of electrons (2e ) from a metal magnesium (Mg) to a non – metal atom chlorine (Cl) It is formed by sharing of electrons between the non-metal atoms carbon and hydrogen
2. In MgCl2 , strong electrostatic force of attraction exist between magnesium cation (Mg2+) and chloride atoms (Cl ) In CH4, weak force of attraction exist between carbon atom and four hydrogen atoms.

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 14.
Why are Noble gases inert in nature?
Answer:
Noble gases have stable valence electronic configuration. So noble gas atoms neither have any tendency to gain nor lose electrons and their valency is zero. Thus they are said to be inert.

III. Answer in detail :

Question 1.
List down the differences between Ionic and Covalent compounds.
Answer:

Ionic Compounds Covalent Compounds
Formed by the transfer of electrons from a metal to a non-metal atom Formed by sharing of electrons between non-metal atoms.
Strong electrostatic force of attraction between cations and anions. Mutual sharing of electrons and so weak force of attraction between atoms.
Solids at room temperature. Gases, liquids and soft solids.
Conducts electricity in molten state or in solutions Non-conductors of electricity.
Have high melting and boiling points. Have low melting and boiling points.
Soluble in polar solvents Soluble in non-polar solvents.
Hard and brittle. Soft and waxy.
Undergo ionic reaction which are fast and instantaneous Undergo molecular reactions which are slow.

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 2.
Give an example for each of the following statements.
(a) A compound in which two Covalent bonds are formed.
(b) A compound in which one ionic bond is formed.
(c) A compound in which two Covalent and one Coordinate bonds are formed.
(d) A Compound in which three covalent bonds are formed.
(e) A compound in which coordinate bond is formed.
Answer:
(a) Oxygen molecule (O2) (O = O)
(b) Sodium’Chloride (NaCl)
(c) Carbon monoxide?
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 1i
(d) Nitrogen molecule (N2) (N ≡N)
(e) NH3 → BF3

Question 3.
Identify the incorrect statement and correct them.
(a) Like covalent compounds, coordinate compounds also contain charged particles (ions). So they; are good conductors of electricity.
(b) Ionic bond is a weak bond when compared to Hydrogen bond.
(c) Ionic or electrovalent bonds are formed by mutual sharing of electrons between atoms.
(d) Loss of electrons is called Oxidation and gain of electron is called Reduction.
(e) The electrons which are not involved in bonding are called valence electrons.
Answer:
(a) Incorrect statement. Like covalent compounds, co-ordinate compounds also do not contain charged particles (ions), so they are bad conductors of electricity.
(b) Incorrect statement. Ionic bond is a strong bond when compared to hydrogen bond.
(c) Incorrect statement. Covalent bonds are formed by mutual sharing of electrons between atoms, (or) Ionic or electrovalent bonds are formed by transfer of electrons between atoms.
(d) Correct statement
(e) Incorrect statement. The electrons which are not involved in bonding are called lone pair of electrons.

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 4.
Discuss in brief about the properties of coordinate covalent compounds.
Answer:
The compounds containing coordinate covalent bonds are called coordinate compounds.
(a) Physical state – These compounds exist as gases, liquids or solids.
(b) Electrical conductivity-Like covalent compounds, co-ordinate compounds also do not contain charged particles (ions), so they are bad conductors of electricity.
(c) Melting point – These compounds have melting and boiling points higher than those of purely covalent compounds but lower than those of purely ionic compounds.
(d) Solubility – Insoluble in polar solvents like water but are soluble in non-polar solvents like benzene, CCl4, and toluene.
(e) Reactions – Co-ordinate covalent compounds undergo molecular reactions which are slow.

Question 5.
Find the oxidation number of the elements in the following compounds.
(a) C in CO2
(b) Mn in MnSO4
(c) N in HNO3
Answer:
(a) C in CO2
1(C) + 2(0) = 0
1x + 2(-2) = 0
x-4 = 0 ‘
x = +4 .
ON of C in CO2 is +4

(b) Mn in MnSO4
1 (Mn) + 1 (S) + 4(0) = 0
x + 1(+6) + 4(-2) = 0
x + 6 – 8 = 0
x – 2 = 0
x = +2
ON of Mn in MnSO4 is +2,

(c) N in HNO3
1(H) + 1 (N) +3(0) =0
1 (+1) + 1 (x) + 3 (-2) =0
+ 1 + x – 6 =0
x – 5 =0
x = +5
ON of N in HNO3 is + 5.

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

9th Science Guide Chemical Bonding Additional Important Questions and Answers

I. Choose the correct answer:

Question 1.
Which of the following atom can exist independently?
(a) Magnesium
(b) Chlorine
(c) Hydrogen
(d) Neon
Answer:
(d) Neon

Question 2.
Alkali and alkaline earth metals form ………… compound when they react with non- metals.
(a) ionic
(b) covalent
(c) co-ordinate covalent
(d) all the above
Answer:
(a) ionic

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 3.
……………..compounds are highly brittle.
(a) Ionic
(b) Covalent
(c) Co-ordinate covalent
Answer:
(a) Ionic

Question 4.
The bond which is formed by mutual sharing of electrons is called ……………….. bond.
(a) ionic
(b) covalent
(c) co-ordinate covalent bond
(d) all the above
Answer:
(b) covalent

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 5.
………………. is an example of a covalent compound having high melting point.
(a) Magnesium oxide
(b) Silicon carbide
(c) Ammonia
(d) All the above
Answer:
(b) Silicon carbide

Question 6.
Which of the following compound(s) possesses high melting point?
(a) NaCl
(b) MgCl2
(c) CCl4
(d) Both a & b
Answer:
(d) Both a & b

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 7.
The element that would form cation due to loss of electron during the chemical reaction is ………………..
(a) calcium
(b) Fluorine
(c) Chlorine
(d) all the above
Answer:
(a) calcium

Question 8.
Fajan’s rule is formulated by considering …………… the of cation and ………………..of the cation and anion.
(a) charge
(b) size
(c) charge & size ’
(d) none
Answer:
(c) charge & size

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 9.
The formation of brown colour on the freshly unit surface of vegetables and fruits is because ………………. of organic compounds present in them.
(a) oxidation
(b) reduction
(c) both a & b
(d) none
Answer:
(a) oxidation

Question 10.
Which of the following compounds has melting and boiling points higher than covalent compounds but lower than ionic compounds?
(a) NaCl
(b) MgCl2
(c) H2O
(d) NH3→BF3
Answer:
(d) NH3→BF3

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 11.
Atoms having 1,2 or 3 electrons in its valence shell will readily form ……………..
(a) cation
(b) anion
Answer:
(a) cation

II. Fill in the blanks:

1. ……………theory explains the formation of molecules.
Answer:
Kossel – Lewis theory

The valency of noble gases is ……………..
Answer:
zero

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

3. …………….. is the only noble gas which does not have eight electrons in their valence sheel.
Answer:
Helium

4. The atom that loses electrons will from a ________
Answer:
cation

5. ______ compounds have high density.
Answer:
Ionic

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

6. In covalent bond formation, the sharing of ………….. electrons takes place in their outermost shell.
Answer:
unpaired

7. Polar solvents contain bond between atoms with ………………
Answer:
different electro negativities

8. ……………….. & ………….. atoms have similar electro negativities.
Answer:
Carbon & hydrogen

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

9. Molecular reactions are ……………… in covalent compound.
Answer:
slow

10. Ionic compounds are ……………..in nature.
Answer:
solid

11. The tendency of atoms to have eight electrons in the outer shell is known as ……………….
Answer:
Octet rule

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

12. As per Fajan’s rule, A1I3is ……………..
Answer:
covalent

13. Oxidising agents are otherwise called as ………………..
Answer:
electron acceptors

14. The tarnishing of metals is due to the formation of ……………….
Answer:
metal oxide

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

15. The tarnishing of metals is an example of ……………. reaction.
Answer:
oxidation

16. The sum of oxidation number of all atoms in a compound is ………………..
Answer:
Zero

17. The ……………….. is a metal that has high resistance to corrosion.
Answer:
Gold

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

III. Spot the error / correct the wrong statement:

Question 1.
In the formation of compounds, the inner shell electrons of an atom involve in bonding.
Answer:
In the formation of compounds, the valence electrons of an atom involve in bonding.

Question 2.
The atom that gains electrons will form cation.
Answer:
The atom that gains electrons will form anion.

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 3.
Ionic compounds have low melting and boiling point.
Answer:
Ionic compounds have high melting and boiling point, (or) Covalent compounds have low melting and boiling point.

Question 4.
Non-polar solvents contain bonds between atoms with different electro negativities.
Answer:
Non-polar solvent contain bonds between atoms with similar electro negativities.

Question 5.
Covalent compounds are soluble in polar solvents.
Answer:
Covalent compounds are readily soluble in non-polar solvents, (or) Ionic compounds are soluble in polar solvents.

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 6.
Greater the charge of the cation greater will be the ionic character.
Answer:
Greater the charge of the cation greater will be the covalent character.

IV. Match the following :

Question 1.

1) Mono atomic gaseous atom a) Electrovalent bond
2) Octet rule b) Benzene
3) Ionic bond c) Water
4) Non-polar solvent d) Electronic theory of valence
5) Polar solvent e) Noble gases

Answer:
1. – e, 2. – d, 3. – a, 4. – b, 5. – c

Question 2.

1) Atomic bond a) Oxygen and hydrogen
2) Atoms with different electro negativities b) acceptor bond
3) Atom which accepts electron pair c) covalent bond
4) Rusting of iron d) donor atom
5) Atom which provides electron pair e) oxidation
f) ionic bond

Answer:
1. – c, 2. – a, 3. – b, 4. – e, 5, – d.

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

V. Find odd one out and write reason :

Question 1.
Water, acetone, benzene, toluene turpentine.
Answer:
Water. It is polar solvent where a^ others air non-polar solvents.

Question 2.
Addition of oxygen, removal of hydrogen, loss of electron, gain of electron.
Answer:
Gain of electron. It is a reduction reaction whereas other three are oxidation reaction.

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 3.
Platinum, palladium NaBH4, CrO3.
Answer:
CrO3 It is an oxidising agent where as other three are reducing agents.

Question 4.
Ionic bond, metallic bond, Co-ordinate covalent bond, Hydrogen bond.
Answer:
Hydrogen bond. It is a weak bond where as other three are strong bonds.

Question 5.
Soft & waxy, bad conductor of electricity, low boiling point, solid at room temperature.
Answer:
Solid at room temperature.
It is the property of ionic compounds whereas other three are the properties of cova-lent compounds.

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding
.
VI. Answer in brief :

Question 1.
What is chemical bond?
Answer:
A chemical bond may be defined as the force of attraction between the two atoms that binds them together as a unit called molecule.

Question 2.
Write the basic concept of Kossel – Lewis theory.
Answer:
Kossle – Lewis theory is based on the concept of electronic configuration of noble gases.

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 3.
Define ionic bond.
Answer:
An ionic bond is a chemical bond formed by the electrostatic attraction between positive and negative ions. The bond is formed between two atoms when one or more electrons are transferred from the valence shell of one atom to the valence shell of the other atom.

Question 4.
The following shows the electronic distribution diagram for the formation of MgCl2 molecule. Based on this answer the following questions.
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 10
(a) Which of the above atom loses electrons to form a cation?
(b) Which of the above atom gain electrons to form anion?
(c) How many electrons are transfered from Mg to Cl?
(d) Write the name of anion formed.
(e) Which noble gas configuration do these ions resemble?
(f) Write the electronic configuration of Mg2+ & Cl
Answer:
(a) Magnesium atom loses electrons to form a cation.
(b) Chlorine atom gains 1 electron to from anion.
(c) Two electrons are transferred from Mg – atom to 2 Cl – atoms (each Cl – atom gains 1e from Mg – atom).
(d) Chloride anion (Cl )
(e) Mg2+ ion resembles noble gas configuration of Neon Cl ion resembles noble gas configuration of Argon.
(f) Electronic configuration of Mg2+ is 2, 8. and Electronic configuration of Cl is 2, 8, 8.

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 5.
What is covalent bond?
Answer:
Bond which is formed between atoms by the mutual sharing of electrons is known as covalent bond.

Question 6.
Name of the following:
(a) An element which obtains the noble gas configuration of neon by losing three electrons.
(b) An element which gains two electrons to obtain noble gas configuration of Neon.
Answer:
(a) Aluminium (Al → Al3+ + 3e)
(b)Oxygen atom (O + 2e → 02-)

Question 7.
Identify the following reactions as oxidation/reduction/redox reaction.

(a) Zn + CuSO4 → Cu + ZnSO4
(b) CuO+H2 → Cu+H2O
(c) 2Mg +O2  → 2MgO
Answer:
(a) Redox reaction
(b) Reduction
(e) Oxidation

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 8.
What are oxidising agents? Give an example.
Answer:
Substances which have the ability to oxidise other substances are called oxidising agents. These are also called as electron acceptors because they remove electrons from other substances. ’
Example:
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 11

Question 9.
What are reducing agents? Give examples.
Answer:
Substances which have the ability to reduce other substances are called reducing agents. These are also called as electron donors because they donate electrons to other substances.
Example: NaBH4, LiAlH4 and metals like Palladium, Platinum.

Question 10.
What are redox reactions? Give examples.
Answer:
Both the oxidation and reduction occurs in the same reaction simultaneously is known as redox reaction. If one reactant gets oxidised, the other gets reduced. Such reactions are called oxidation-reduction r-eaqtions or redox reactions.
Ex. 1 : 2 PbO + C → 2 Pb + CO2
Ex. 2 : Zn + CuSO → Cu + ZnSO4

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 11.
Define (a) oxidation (b) reduction reactions : Give examples.
Answer:
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 12

Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 13

Question 12.
What is rancidity?
Answer:
The oxidation reaction in food materials that were left open for a long period is responsible for spoiling of food. This is called rancidity.

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 13.
Define oxidation number.
Answer:
Oxidation number of an element is defined as the formal charge which an atom of that element appears to have when electrons are counted.

Question 14.
Identify the type of bond in \(\mathrm{NH}_{4}^{+}\)
E:\jyothi\images\2\Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 21.png
Answer:
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 21

VII. To interpret:

Question 1.
Ionic bond is also called electrostatic bond.
Answer:
In ionic bond formation the bond is formed between the oppositely charged ions and these ions come closer to each other due to electrostatic force of attraction. So ionic bond is also called electrostatic bond.

Question 2.
Ionic compounds are crystalline solids at room temperature.
Answer:
Ionic compounds are formed because of the strong electrostatic force between cations and anions which are arranged in a well-defined geometrical pattern. Thus ionic compounds are crystalline solids at room temperature.

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 3.
Covalent compounds have low melting point.
Answer:
In covalent compounds, atoms are held by weak force of attraction. When heat is applied, the molecules are readily pulled out and get free movement.

VIII. Assertion and Reason type questions :

Question 1.
Statement (A) : Ionic compounds do not conduct electricity in solid state.
Reason (B) : The ions in ionic compounds are tightly held together by strong electrostatic force of attraction and they can not move freely.
(a) B explains A
(b) B do not explain A
(c) B is wrong A
(d) A is right B is wrong
Answer:
(a) B explains A

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 2.
Statement (A) : Covalent compounds are bad conductor of electricity.
Reason (B) : Covalent compounds contain charged particles (ions)
a) B explains A
b) B does not explain A
c) Both A & B are right
d) Both A & B are wrong
Answer:
(b) B does not explain A
Reason : Since covalent compounds do not have charged particles (ions), they are bad conductor of electricity.

IX. Find the oxidation number of the elements in the following compounds.

(1) Zn in ZnSO4
(2) Ca in CaH2
(3) Mg in MgO
(4) N in NH3
(5) A1 in AlCl3
Answer:
(1) ZnSO4
1(Zn) + 1 (S) + 4 (0) = 0
x + 1(+6) + 4(-2) = 0
x + 6 – 8 = 0
x = + 2
Oxidation number of Zn in ZnSO4 is +2

(2) CaH2
1(Ca) + 2 (H) = 0
x + 2 (-1) = 0
x -2 = 0
x = + 2
Oxidation number of Ca in CaH2 is +2

(3) MgO
1(Mg) + 1 (O) = 0
x + 1 (-2) = 0
x -2 = 0
x = + 2
Oxidation number of Mg in MgO is +2

(4) NH3
1(N) + 3 (H) = 0
x + 3 (-1) = 0
x – 3 = 0
x = +3
Oxidation number of N in NH3 is +3
(5) AlCl3
1(Al) + 3(Cl) = 0
x + 3 (-1) = 0
x – 3 = 0
x = + 3
Oxidation number of Al in AlCl3 is +3

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

X. Complete the following table:

Question 1.

Atoms Atomic number Electron distribution
a) O 8
b) N
c) – 17
d) – 2,8,2

Answer:

Atoms Atomic number Electron distribution
a) O 8 2,6
b) N 7 2,5
c) Cl 17 2,8,7
d) Mg 12 2,8,2

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 2.

a) Dativebond
b) CaH2 → Ca+H2
c) – Reduction
d) – Redox reaction

Answer:

a) Dativebond Co-ordinate covalent bond
b) CaH2 → Ca+H2 Oxidation
c) Fe3+ + e →Fe2+ Reduction
d) both Oxidation of Reduction takes plase simultaneously Redox reaction

XI. To Match:

Name of compound Type of compound
a) Sodium chloride ?
b) ? co-ordinate covalent compound
c) Methane ?
d) Fluorine molecule ?

Answer:

Name of compound Type of compound
a) Sodium chloride Ionic compound
b) NH3 → BF3 co-ordinate covalent compound
c) Methane Covalent compound
d) Fluorine molecule Covalent compound

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

XII. Answer in detail :

Question 1.
Explain the ionic bond formation in sodium chloride with electron distribution diagram.
Answer:
Formation of Sodium Chloride (NaCl)

(i) The atomic number of Sodium is 11 and its electronic configuration is 2, 8, 1. It has one electron excess to the nearest stable electronic configuration of a noble gas – Neon.

(ii) So sodium has a tendency to lose one electron from its outermost shell and acquire a stable electronic configuration forming sodium cation (Na+).

(iii) The atomic number of chlorine is 17 and its electronic configuration is 2, 8, 7. It has one electron less to The nearest stable electronic configuration of a noble gas – Argon.

(iv) So chlorine has a tendency to gain one electron to acquire a stable electronic
configuration forming chloride anion (Cl)
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 15

(v) When an atom of sodium combines with an atom of chlorine, an electron is transferred from sodium atom to chlorine atom forming sodium chloride molecule. Thus both the atoms achieve stable octet electronic configuration.

Question 2.
Explain the covalent bond formation in the following molecules.
(a) Chlorine
(b) Nitrogen .
(c) Hydrogen
(d) Oxygen
Answer:
(a) Chlorine
Chlorine molecule is formed by two chlorine atoms. Each chlorine atom has seven valence electrons (2,8,7). These two atoms achieve a stable completely filled electronic configuration (octet) by sharing a pair of electrons.
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 14

(b) Nitrogen
Nitrogen molecule is formed by two nitrogen atoms. Each nitrogen atom has five valence electrons (2, 5). These two atoms achieve a stable completely filled electronic configuration (octet) by sharing three pair of electrons. Hence a triple bond is formed in between the two atoms.

(c)Hydrogen
Hydrogen molecule is formed by two hydrogen atoms. Both hydrogen atoms contributes one electron each to the shared pair and both atoms acquire stable completely filled electronic configuration.
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 18

(d) Oxygen
Oxygen molecule is formed by two oxygen atoms. Each oxygen atom has six valence electrons (2,6). These two atoms achieve a stable electronic configuration (octet) by sharing two pair of electrons. Hence a double bond is formed in between
the two atoms.
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 19

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 3.
Explain the co-ordinate covalent bond formation in between NH3 → BF3 molecules.
Answer:
The ammonia molecule gives a lone pair of electrons to boron tri fluoride (BF3) molecule which is electron deficient. Thus a co-ordinate covalent bond is formed between NH3 (donor molecule) and BF3 (acceptor molecule) and is represented by
Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding 20

Question 4.
Write notes on characteristics of covalent compounds.
Answer:
a. Physical state : Depending on force of attraction between covalent molecule the bond may be weaker or stronger. Thus covalent compounds exists in gaseous, liquid and solid form. Eg. Oxygen-gas; Water-liquid: Diamond-solid.

b. Electrical conductivity : Covalent compounds do not contain charged particles (ions), so they are bad conductors of electricity.

c. Melting point : Except few covalent compounds (Diamond, Silicon carbide), they have relatively low melting points compared to Ionic compounds.

d. Solubility : Covalent compounds are readily soluble in non-polar solvents like benzene (C6H6), carbon tetra chloride (CCl4). They are insoluble in polar solvents like water.

e. Hardness and brittleness : Covalent compounds are neither hard nor brittle. But they are soft and waxy.

f. Reactions : Covalent compounds undergo molecular reactions in solutions and these reactions are slow.

 Samacheer Kalvi 9th Science Guide Chapter 13 Chemical Bonding

Question 5.
Write notes on characteristics of ionic compounds.
Answer:
a. Physical state : These compounds are formed because of the strong electrostatic force between cations and anions which are arranged in a well-defined geometrical pattern. Thus ionic compounds are crystalline solids at room temperature.

b. Electrical conductivity : Ionic compounds are crystalline solids and so their ions are tightly held together. The ions, therefore, cannot move freely, so they do not conduct electricity in solid state. However, in molten state and their aqueous solutions conduct electricity.

c. Melting point: the strong electrostatic force between the cations and anions hold the ions tightly together, so very high energy is required to separate them. Hence ionic compounds have high melting and boiling points.

d. Solubility : Ionic compounds are soluble in polar solvents like water. They are insoluble in non-polar solvents like benzene (C6H6), carbon tetra chloride (CCl4).

e. Density, hardness and brittleness : Ionic compounds have high density and they are quite hard because of the strong electrostatic force between the ions. But they are highly brittle.

f. Reactions : Ionic compounds undergo ionic reactions which are practically rapid and instantaneous.

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