Samacheer Kalvi 9th Science Solutions Chapter 13 Pdf

Tamilnadu Board Samacheer Kalvi 9th Science Solutions Chapter 13: Tamilnadu State Board Solution Class 10 Science Chapter 13 – Chemical Bonding.

Samacheer Kalvi 9th Science Solutions Chapter 13: Overview

Board	Samacheer Kalvi
Class	9
Subject	Science
Chapter	13
Chapter Name	Chemical Bonding

Samacheer Kalvi 9th Science Solutions Chapter 13 Chemical Bonding

I.) Choose the correct answer.

(1.) Number of valence electrons in carbon is

a) 2

b) 4

c) 3

d) 5

Ans:b) 4

Explanation: Because, the atomic no. of carbon is 6 and having electronic configuration as 2, 4.

And hence, its valence electrons are 4.

(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

Ans: c) Lose one

Explanation: Because, the atomic no. of sodium is 11 and having electronic configuration as 2, 8, 1.

And hence by losing 1 valence electron attains the nearest Noble gas configuration

(3.) The element that would form anion by gaining electrons in a chemical reaction is _______________

a) Potassium

b) Calcium

c) Fluorine

d) Iron

Ans: c) Fluorine

Explanation: Because, the atomic no. of Fluorine is 9 and having electronic configuration as 2, 7.

And hence, it has only one electron less to complete its octet, so in order to completeits octet it gain one electron by forming anion.

(4.) Bond formed between a metal and nonmetal atom is usually __________

a) Ionic bond

b) Covalent bond

c) Coordinate bond

Ans: a) Ionic bond

Explanation: Because, the bond formed between metal and nonmetal is ionic bond.

(5.) ______________ compounds have high melting and boiling points.

a) Covalent

b) Coordinate

c) Ionic

Ans:c) Ionic

Explanation: Because, the ionic bond if formed between two ions of opposite charges due to the electrostatic force of attraction between them. So they have high melting and boiling point.

(6.) Covalent bond is formed by __________

a) Transfer of electrons

b) Sharing of electrons

c) Sharing a pair of electrons

Ans:b) Sharing of electrons

Explanation: Because, covalent bond is formed due the sharing of electrons which are common to both the atoms.

(7.) Oxidizing agents are also called as ___________ because they remove electrons form other substances.

a) Electron donors

b) Electron acceptors

Ans:b) Electron acceptors

Explanation: Because, they have ability to oxidize other substances by removing the electrons from other substances.

(8.) Elements with stable electronic configurations have eight electrons in their valence shell. They are ___

a) Halogens

b) Metals

c) Noble gases

d) Non-metals

Ans:c) Noble gases

Explanation: Because, Noble gas elements have all the shells completely filled.

Answer briefly.

(1) How do atoms attain Noble gas electronic configuration?

Ans:

All the Noble gases except Helium have 8 electrons in their valence shell and thus have stable valence shell electronic configuration. And they neither have tendency to gain nor is to lose electrons and hence having valency zero.

In 1916 Kossel and Lewis proposed a theory known as electronic theory of valence or Octet rule. According to this theory, atoms of all elements other than inert gases combine to form molecules because they have incomplete valence shell and attains the nearest stable Noble gas electronic configuration.

This is done by either transfer of electrons from one atom to other or by sharing of valence electrons in order to achieve the stable outer shell of eight electrons.

For example: in NaCl, Na has electronic configuration as 2, 8, 1 and Cl has electronic configuration as 2, 8, 7.

Thus, Na loses 1 electron to achieve stable electronic configuration and this electron is gained by Cl atom which has 1 electron less to complete its outermost shell.

(2) NaCl is insoluble in carbon tetrachloride but soluble in water. Give reason.

Ans:

NaCl is an ionic compound formed by the losing one electron form Na atom which is gained by Cl atom. There is electrostatic force of bonding in Na⁺ ions and Cl^– ions, due which it forms the strong ionic bonding.

And hence, this ionic compound is easily soluble in polar solvent only, and water is the polar solvent.

Because, polar solvents contain bonds between atoms with very different electro negativities, such as oxygen and water.

While carbon tetrachloride is the nonpolar solvent in which NaCl cannot soluble.

Hence, NaCl is soluble in water and insoluble in carbon tetrachloride.

(3) Explain Octet rule with an example.

Ans:

In order to attain the stable Noble gas electronic configuration atoms lose or gain the electrons.

So that their outermost valence shell will be completely filled.

The tendency of atoms to have eight electrons in the valence shell is known as Octet rule or Rule of eight.

For example: sodium has atomic no. 11 with electronic configuration as 2, 8, 1. Hence, it loses one electron in order to achieve nearest stable Noble gas electronic configuration and thereby its valence shell will be filled with 8 electrons i.e. Octet rule.

Similarly, chlorine has atomic no. 17 with electronic configuration as 2, 8, 7 and it needs only one electron to complete its octet and becomes stable. So it gain one electron so that its valence shell will be completely filled i.e. Octet rule.

(4) Write a note on different types on bonds.

Ans;’

All the atoms have different valence shell electronic configuration, so the ways to combine and forms the compounds is different for different atoms. The compounds or molecules are formed by three types of bonding which are given as below.

Ionic or Electrovalent bond:

An ionic bond is the chemical bond formed by the electrostatic attraction between the positive and negative ions.

In this bond formation, one atom loses the electrons by forming positive ion and this electrons will be received by another atom to form negative ion. And hence, due to electrostatic attraction ionic bond is formed between them. The atoms transfers or receives the electrons to attain stable Noble gas electronic configuration.

For example; NaCl is formed by ionic bond formation

Covalent bond:

Atoms forms the compound by sharing of unpaired electrons from their outermost shell. Each of the atom combining contributes the one electron to the electron pair which is required for the bond formation. Thus by sharing the electrons atoms attains the nearest stable Noble gas electronic configuration and the bond formed is called as covalent bond.

For example:Cl₂ molecule is formed by the Covalent bonding formation.

Coordinate Covalent bond:

In some compounds, the formation of covalent bond between two atoms takes place by the sharing of two electrons, both of which comes from only one of the combining atoms. This bond is called as Coordinate covalent bond or Dative bond.

For example: Coordinate covalent bond is formed between NH₃=> BF₃ molecules

(5.) Correct the wrong statements.

Ionic compounds dissolve in non-polar solvents.

Ans: Correct statement: Ionic solvents dissolve in polar solvents.

Because, ionic compound are formed by strong electrostatic attraction between positive and negative ions, and hence they are soluble in polar solvents and insoluble in non-polar solvents.

Because, polar solvents contain bonds between atoms with very different electro negativities, such as oxygen and water.

b.) Covalent compounds conduct electricity in molten or solution state.

Ans: Correct Statement:Ionic compounds conducts electricity in molten or solution state.

Covalent compounds are non-conductors of electricity.

(6) Complete the table give below.

Ans:

Element	Atomic Number	Electron distribution	Valence electrons	Lewis dot structure
Lithium	3	2, 1	1
Boron	5	2, 3	3
Oxygen	8	2, 6	6

(7) Draw the electron distribution diagram for the formation of Carbon di oxide (CO2) molecule.

Ans:

The carbon atom has atomic no. 6 with electronic configuration as 2, 4.
And oxygen atom has atomic no. 8 with electronic configuration as 2, 6.
One carbon atom shares its 4 electrons with 2 oxygen atoms to form the two C=O covalent bonds, and carbon dioxide is formed.

(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

Ans:

Ionic bond	Covalent bond	Coordinate covalent bond
CaCl₂	H₂O, HF	CO
CaO	CO₂
KBr, HCl	CCl₄ and Al₂Cl₆

Because, Ca atom has atomic no. 20 with electronic configuration as 2, 8, 8, 2.
Hence to attain nearest Noble gas electronic configuration it loses 2 electrons and forms Ca²⁺
Similarly, each Cl atoms gain 1 electron to complete its octet and forms Cl^–
Thus, Ca²⁺ ions attracts the 2 Cl^– ions and forms the ionic bonding.
In the same way, CaO and KBr formed by ionic bonding in order to attain nearest Noble gas electronic configuration.
In H₂O, each hydrogen atom shares one electron with the oxygen atom and thereby sharing the electron in common of both hydrogen and oxygen forms the covalent bond.
Similarly, in CO₂, CCl₄ and Al₂Cl₆ covalent bond is formed.
CO is formed by the Coordinate covalent bond.

(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.

Ans: B. it is hard and brittle.

Because, the ionic bond is formed due to the strong electrostatic force of attraction bet cation and anion and completes their octet by forming ionic bond. Thus, they are strong means hard.

They are also brittle, because in a crystal when charged ions come together and strong electrostatic repulsion distort the crystal.

10.) Identify the following reactions as oxidation or reduction

Ans:

a. Na → Na+ + e

The above reaction shows oxidation reaction.

The chemical reaction which involves the addition of oxygen or removal of hydrogen atom or loss of electrons is called as oxidation reaction.

Here, Na atom has atomic no. 11 with electronic communication 2, 8, 1 and hence loses one Valence electron to attain nearest stable Noble gas electronic configuration to form Na + ion.

b. Fe3+ + 2 e-→ Fe+

The above reaction shows the reduction reaction.

The chemical reaction which involves the addition of hydrogen atom or removal of oxygen or gain of electrons is called as reduction reaction.

Here, Fe³⁺ gains to electrons to form Fe⁺ and hence show reduction reaction.

11.) Identify the compounds as Ionic/ Covalent/Coordinate based on the given characteristics.

Ans:

a. Soluble in non-polar solvents: Covalent compounds

Since, covalent compounds are readily soluble in non –polar solvents like Benzene, Carbon tetrachloride. And they are insoluble in polar solvents like water.

b. Undergoes faster/instantaneous reactions: Ionic compounds

Since, ionic compounds undergoes reactions which practically faster and rapid.

c. Nonconductors of electricity: Covalent compounds

Since, covalent compounds does not contains any charged ions and hence, they are the non-conductors of electricity

d. Solids at room temperature:Ionic compounds

Since, ionic compounds are formed because of the strong electrostatic force of attraction between positive and negative ions which arranged in a periodic geometrical pattern. And hence ionic compounds are crystalline solids at room temperature.

(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.

Ans:

The atomic no. of Ca is 20 with electronic configuration as 2, 8, 8, 2. That means it attains nearest Noble gas electronic configuration by losing 2 electrons and forms the Ca²⁺
The oxygen atom has atomic no. 8 with electronic configuration 2, 6. It requires two electrons to complete its octet.
So Ca shares its 2 electrons with one oxygen atom. The shared electrons are common to both and hence, octet of both is completed by forming the covalent bond. And hence, the ionic compound CaO is formed.

(13.) Considering MgCl2 as ionic compound and CH4 as covalent compound give any two differences between these two compounds.

Ans:

MgCl₂:

It is crystalline solid at room temperature.
It do not conducts electricity in solid state but in molten state its aqueous solution conducts electricity.
It has high melting and boiling point due to strong ionic bond formation.
It is soluble in polar solvent only.

CH₄:

The covalent bond formed is weaker, so it is in gaseous state at room temperature.
It does not contains any charged ions hence it is bad conductor of electricity.
It has relatively low melting point.
It is soluble in non-polar solvent only.

(14.) Why are Noble gases inert in nature?

Ans:

The noble gas elements or zero group elements or 18^th group elements are inert in nature. Because, they have all the shells which completely filled. So they are having most stable electronic configuration.

They are the most stable elements in the periodic table. They exist in single form only and does not reacts more with other elements due to their most stability. So it is very difficult to change their structures or to remove the electrons from valence shell also.

The noble inert gas elements are Helium, Neon, Argon, Krypton, Xenon and Radon.

III. Answer in detail

1) List down the differences between Ionic and Covalent compounds.

Ans:

Ionic Compounds:

They are formed by the strong electrostatic force of attraction between positive and negative ions.
They are in the form of crystalline solids at room temperature.
They do not conducts electricity in solid state but in molten state its aqueous solution conducts electricity.
They have high melting and boiling point due to strong ionic bond formation.
They are soluble in polar solvent only and insoluble in nonpolar solvents.
They are highly dens and brittle in nature.
They undergoes reactions which are fast and instantaneous.

Covalent Compounds:

They are formed by the sharing of electrons which are common to both the atoms after bond formation.
On the basis of the covalent bond formed which may weaker or stronger, they exist in gaseous, liquid and solid state also.
They do not contains any ions and hence bad conductors of electricity.
They have relatively low melting point.
They are soluble in nonpolar solvents and insoluble in polar solvents.
They are soft and waxy in nature.
They undergoes the molecular reactions which are slow.

2) Give an example for each of the following statements.

Ans:

a. A compound in which two Covalent bonds are formed:

Example: O₂ molecule formation

O₂ molecule is formed by two oxygen atoms. Each oxygen atom has 6 valence electrons, these two oxygen atoms attains stable electronic configuration by sharing two lone pair of electrons common to both. Thus double bond is formed between them which is covalent in nature.

Fig. Formation of two covalent bond in O₂ molecule

b. A compound in which one ionic bond is formed:

Example: NaCl formation

When an atom of sodium combines with an atom of chlorine, an electron is transferred from sodium to chlorine atom forming the ionic bond between them. And both attains the stable electronic configuration by the formation of ionic bond between them.

c. A compound in which two Covalent and one Coordinate bonds are formed:

Example; NH₃→BF₃molecule formation

Here, the molecule of ammonia gives a lone pair of electrons to Boron trifluoride molecule which has electron deficiency. Thus, coordinate covalent bond is formed between NH₃and BF₃molecules. Which is given by NH₃ →BF₃.

d. A compound in which three covalent bonds are formed:

Example: N₂ molecule formation

Here, nitrogen molecule is formed by the two nitrogen atoms. Each nitrogen atom has 5 valence electrons. These two nitrogen atoms shares three lone pairs of electrons in common and attains the stable electronic configuration. Hence, triple bond is formed between them which is covalent in nature.

e. A compound in which coordinate bond is formed:

Example: formation of NH₄⁺ ion
In NH₃ molecule, central nitrogen atom has 5 valence electrons out of which 3 electrons are shared with 3 hydrogen atoms and also it has one lone pair of electron remained.

This lone pair is shared with H⁺ ion and thus N→H coordinate covalent bond is formed between them. And NH₄⁺ molecule is formed.

3) Identify the incorrect statement and correct them.

Ans:

a. Like covalent compounds, coordinate compounds also contain charged particles (ions). So they are good conductors of electricity.

Correct statement: Like covalent compounds, coordinate compounds also contain charged particles (ions). So they are bad conductors of electricity.

b. Ionic bond is a weak bond when compared to Hydrogen bond.

Correct statement: Ionic bond is formed due to the electrostatic force of attraction between cation and anion and hence this bond is strong as compared to Hydrogen bond.

c. Ionic or electrovalent bonds are formed by mutual sharing of electrons between atoms.

Correct Statement:The ionic bond is formed by transfer of valence electron of one atom to the other atom. The atom which loses electron becomes positive and called as cation. And the atom which gain this electrons becomes negative which is called as anion.

d. Loss of electrons is called Oxidation and gain of electron is called Reduction.

Correct statement: Oxidation is the loss of electrons and reduction is the gain of electrons.

e. The electrons which are not involved in bonding are called valence electrons.

Correct statement: The electrons which are involved in bonding are called as valence electrons.

4) Discuss in brief about the properties of coordinate covalent compounds.

Ans:

The compounds containing coordinate covalent bond are called as coordinate covalent compounds.
Physical state: these compounds exist in the form of gases, liquids or solids.
Electrical conductivity: like covalent compounds, the coordinate compounds also does not contain charged ions and hence they are bad conductors of electricity.
Melting point: the melting point and boiling point of coordinate compounds is higher than purely covalent compound and less than the purely ionic compound.
Solubility: they are soluble in non-polar solvents like Benzene, CCl₄ and toluene. But they are insoluble in polar solvents like water.
Reactions: coordinate covalent compounds undergoes molecular reactions which are slow.

5) Find the oxidation number of the elements in the following compounds.

Ans:

a) C in CO₂: Here, in CO₂ formation Carbon atom shares all its 4 valence electrons in bond formation. Hence the oxidation no. of C in CO₂ is +4.

b.) Mn in MnSO₄: Here, in the formation of MnSO₄, Mn loses 2 electrons to attain stable electronic configuration. Hence, the oxidation no. of Mn in MnSO₄ is +2

c.) N in HNO₃: Here, in the formation of HNO₃, nitrogen atom shares its 5 valence electrons to attain stable electronic configuration. Hence, the oxidation no. of N in HNO₃ is +5