Kerala Syllabus Class 9 Chemistry Chapter 3 Chemical Bonding Notes Solutions

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Kerala SCERT Class 9 Chemistry Chapter 3 Solutions Chemical Bonding

Kerala Syllabus Std 9 Chemistry Chapter 3 Chemical Bonding Notes Solutions Questions and Answers

Class 9 Chemistry Chapter 3 Let Us Assess Answers Chemical Bonding

Question 1.
Draw the electron dot diagram of hydrogen (H), helium (He), lithium (Li), beryllium (Be) and fluorine (F).
Answer:

Question 2.
Illustrate the formation of the chemical bond in chlorine (Cl₂) using an electron dot diagram as illustrated in the fluorine (F₂) molecule.
Answer:

Question 3.
Represent the covalent bond in chlorine molecules using symbols.
Answer:
Cl – Cl

Question 4.
Represent the formation of ionic bonds in the following ionic compounds using the electron dot diagram and orbit model.
a) Sodium fluoride (NaF)
b) Sodium oxide (Na₂O)
c) Magnesium fluoride (MgF₂)
d) Calcium oxide (CaO)
Answer:

Question 5.
Assume that calcium (Ca) and fluorine (F) combine.
a) Complete the following table accordingly.

Element	Atomic number	Electronic configuration	Number of electrons received or donated
Ca	20	……………………………	………………………………….
F	9	……………………………..	……………………………..

b) Write the chemical formula of calcium fluoride.
c) Similarly, write the chemical formula of magnesium chloride and aluminium chloride.
Answer:

Element	Atomic number	Electronic configuration	Number of electrons received or donated
Ca	20	2, 8, 8, 2	2
F	9	2,7	1

b) CaF₂

c)

Element	Atomic number	Electronic configuration	Number of electrons received or donated
Mg	12	2, 8, 2	2
Al	13	2, 8, 3	3
Cl	17	2, 8, 7	1

Magnesium chloride – MgCl₂
Aluminium chloride – AlCl₃

Question 6.
Some cations and anions are given in the table. Fill in the blanks.

Answer:

Question 7.
Complete the following chemical equations and answer the questions given below.
(Hint: Atomic number Mg – 12, Cl – 17)
Mg → Mg²⁺ + ________
Cl + 1 e^– → ________
________ + ________ → MgCl²
(a) Identify the cation and anion in these compounds.
(b) What is the nature of the chemical bond in MgCh?
Answer:
Mg → Mg²⁺ + 2e^–
Cl + l e^– → Cl^–
Mg²⁺ + 2Cl^– → MgCl₂

(a) Cation – Mg²⁺
Anion – Cl^–
(b) Ionic bonding

Question 8.
Complete the following table. (Hint: Atomic number F – 9, H – 1, O – 8, N – 7)

Answer:

Question 9.
Complete the following table. (Symbols are not real)

Element	Atomic number	Electron configuration
P	12	………………..
Q	………………..	2, 7
R	10	………………..
S	17	………………..

a) Which among these is the most stable element?
b) Which element donates electrons during chemical reactions?
c) Write the chemical formula of the compound formed when the elements P and S combine.
Answer:

Element	Atomic number	Electron configuration
P	12	2, 8, 2
Q	9	2, 7
R	10	2, 8
S	17	2, 8, 7

a) R is the most stable element.
b) P is the element that donates electrons.

Formula – PS₂

Question 10.
Atom models of two elements are represented below.

a) Draw the electron dot diagram of the formation of sodium fluoride.
b) What is the nature of the chemical bond in sodium fluoride?
c) Write any two characteristics of compounds having this type of bond.
Answer:
a)
b) Ionic bond
c)

• Dissolves in polar solvents like water.
• Exhibits high melting and boiling points.
• Conducts electricity in a molten state or solutions.

Question 11.
The electron configuration of the elements P, Q, and R are given below. (Symbols are not real)
P – 2, 8, 6
Q – 2, 8, 1
R – 2, 8, 8
a) Which is the most stable element among these? What is the reason?
b) What is the atomic number of Q?
c) Draw the atom model of Q.
d) What are the valencies of the elements P and Q?
e) Write the chemical formula of the compound formed when P and Q combine.
Answer:
a) R is the most stable element among these. Because it has a stable octet electron configuration in
the outermost shell.
b) Atomic number of Q = 11
c)
d) Valency of P = 2
Valency of Q = 2

e)
Formula – Q₂P

Question 12.
A, B, C and D are four elements (Symbols are not real). Information about them is given in the following table.

Element	Atomic number	Electronegativity
A	6	2.55
B	8	3.44
C	12	1.31
D	17	3.16

Based on these, find the type of bond in the compounds formed by the combination of the
following pairs of elements.
1. C, B
2. C, D
3. A, B
Answer:
1. C, B
Difference in electronegativity = 3.44 – 1.31 = 2 : 13
Greater than 1.7, so it is ionic bonding.

2. C, D
The difference in electronegativity = 3.16 – 1.31 = 1.85
Greater than 1.7, so it is ionic bonding.

3. A, B
Difference in electronegativity = 3.44 – 2.55 = 0.89
Less than 1.7, so it is covalent bonding.

Extended Activities

Question 1.
Magnesium nitride is obtained when nitrogen is passed over heated magnesium. Write the chemical equation of this reaction. Find out whether the formed compound is ionic or covalent using the electronegativity scale given in this unit. (Hint – Valency: Nitrogen – 3, Magnesium – 2)
Answer:
The chemical equation for the reaction is 3Mg + N₂ → Mg₃N₂
The difference in electronegativity = 3.04 – 1.31 = 1.73
Greater than 1.7, so it is an ionic compound.

Question 2.
Draw the electron dot diagram of the chemical bonds in ethane (C₂H₆), ethene (C₂H₄) and ethyne (C₂H₂). Find out whether these compounds are ionic or covalent. Calculate the total number of bonds in each compound.
Answer:
a) Ethane (C₂H₆)

Total number of bonds = 7

b) Ethane (C₂H₄)

Total number of bonds = 5

c) Ethyne (C₂H₂)

Total number of bonds = 3

Question 3.
Conduct the experiment arranging the apparatus as shown in the figure.

Record your observations and identify what types of compounds are sodium chloride and glucose.
Answer:
The galvanometer in the first experiment shows deflection, indicating that electricity passes through a common salt solution. This observation also notes that gases evolve from metal rods. Thus, common salt is confirmed as an ionic compound, as ionic compounds conduct electricity in their molten state or solutions.

No deflection is observed in the second experiment, signifying that electricity does not pass through the glucose solution. Therefore, glucose is identified as a covalent compound. Typically, covalent compounds do not conduct electricity.

Question 4.
Draw the chemical bonds in different compounds and exhibit them on the bulletin board.
Answer:

Cl – Cl


a)
b) Ionic bond
c)

• Dissolves in polar solvents like water.
• Exhibits high melting and boiling points.
• Conducts electricity in a molten state or solutions.

Chemical Bonding Class 9 Notes Questions and Answers Kerala Syllabus

Question 1.
Some substances are given below. Differentiate them into elements and compounds and list them.
Potassium, oxygen, water, common salt, nitrogen, helium, hydrogen, and sugar.

Answer:

You know that there are two atoms in one molecule of hydrogen. If so, how many atoms are there in each substance given.

Question 2.
How many atoms are there in each substance given below?

Answer:

Molecule	Number of atoms
Oxygen (O2)	2
Water (H2O)	3
Nitrogen (N2)	2
Helium (He)	1
Methane (CH4)	5
Sugar (C12H22O11)	45

Some molecules have more than one atom.

Question 3.
Why do atoms in a molecule stay together?
Answer:
The atoms of a molecule stay together because of chemical bonds.

Question 4.
Why do atoms combine to form molecules?
Answer:
An atom combines in order to attain stability. Also, different compounds are formed by the combination of different atoms.

Question 5.
How do atoms combine?
Answer:
Atoms can combine either by sharing electrons or by completely transferring the electrons.

Question 6.
Do all atoms combine in the same way?
Answer:
No, not all atoms combine in the same way.

Question 7.
Do all atoms combine with other atoms?
Answer:
Not all atoms combine with other atoms.

Question 8.
How many atoms are there in a molecule of noble gases?
Answer:
One atom only.
Generally, noble gases do not combine with other atoms due to their stability. They are able to exist independently. Examples of noble gases, along with their atomic number and electronic configuration, are given in the table below.

Element (Symbol)	Atomic number	Electronic Configuration
Helium (He)	2	2
Neon (Ne)	10	2, 8
Argon (Ar)	18	2, 8, 8
Krypton (Kr)	36	2, 8, 18, 8
Xenon (Xe)	54	2, 8, 18, 18, 8
Radon (Rn)	86	2, 8, 18, 32, 18, 8

Question 9.
How many electrons are there in the outermost shell of noble gases except helium?
Answer:
Eight electrons.
The atomic number of helium is 2; hence, it contains a maximum of two electrons in its outermost shell. All the other noble gases have a total of eight electrons in their outermost shell.

The arrangement of eight electrons in the outermost shell is called octet configuration.

Atoms having octet configuration are more stable. Such atoms are generally reluctant to take part in chemical reactions. So noble gases are also called inert gases. In the case of helium, the configuration is called duplet configuration, which is stable like that of the other noble gases.

Question 10.
Look at the electron configuration of magnesium and oxygen given in the table.

Element	Atomic number	Electronic configuration
Magnesium	12	2, 8, 2
Oxygen	8	2, 6

(i) Are these atoms stable?
(ii) How can they attain stability?
(iii) What is the name of the compound formed when these atoms combine?
Answer:
(i) No
(ii) Stability can be attained by gaining octet electron configuration in the outermost shell through chemical bonding. (In here, magnesium must lose two electrons, and oxygen must gain two- electrons).
(iii) Magnesium oxide (MgO).
The force that binds together the component particles in a compound is called chemical bonding,

Question 11.
The chemical name of table salt is sodium chloride. Answer the following questions.
(i) What are the constituent elements of sodium chloride?
(ii) Write the electron configuration of the sodium atom (atomic number – 11).
(iii) How many electrons are there in the outermost shell of a sodium atom?
(iv) How does the sodium atom attain octet electron configuration?
Answer:
(i) Sodium and Chlorine
(ii) ₁₁Na – 2, 8, 1
(iii) One atom
(iv) By losing one electron in the outermost shell.
In the case of a sodium atom, it loses one electron and changes into a sodium ion.
Na → Na⁺ + le^–

The removal of the outermost electron from the sodium atom can only be achieved by overcoming the force of attraction exerted by the nucleus.

This energy required, or in other terms, the amount of energy required to remove the most loosely bound electron from the outermost shell of an isolated gaseous atom of an element is called its ionisation energy or ionisation enthalpy.

The amount of energy required to remove the most loosely bound electron from the outermost shell of an isolated gaseous atom of an element is called its ionisation energy.

Question 12.
Write the electron configuration of a chlorine atom (atomic number 17).
Answer:
₁₇Cl – 2, 8, 7

Question 13.
How many electrons are needed for the chlorine atom to attain octet electron configuration?
Answer:
One.
I Non-metals like chlorine accept an electron to become a chloride ion.

Energy is released when atoms become negative ions by accepting electrons. This energy released when an electron is added to a neutral gaseous atom to form a negative ion is called electron gain enthalpy.

Illustrate the electron exchange in the formation of sodium chloride through shell electron configuration.

Question 14.
Represent the electron dot diagram of a chlorine atom.
Answer:


The electron dot diagram of the formation of sodium chloride can be represented as

Question 15.
Observe the electron dot diagram and shell electron configuration diagram of sodium chloride formation and complete the table.

Answer:

The equations of the electron transfer during the formation of sodium-chloride are:
Na → Na⁺ + le^–
Cl + le- → Cl^–
In, the reaction between sodium and chlorine to form sodium chloride, the sodium atom loses one electron and gets converted into sodium ion (Na⁺). The chlorine atom accepts an electron to form a chloride ion (Cl^–).

The positive ions formed by losing electrons during chemical reactions are called cations, and the negative ions formed by accepting electrons are called anions.

The particles Na⁺ and Cl^–, which possess opposite charges, show mutual attraction and are bound together by an extremely strong electrostatic force of attraction, resulting in the formation of NaCl.

The electrostatic force of attraction that holds together the oppositely charged ions in an ionic compound is called an ionic bond. An ionic bond is also known as an electrovalent bond. An ionic bond is always formed between a metal and a non-

Question 16.
What is the compound formed when magnesium burns in the air?
Answer:
Magnesium oxide (MgO)
The equation for the chemical reaction between magnesium and oxygen can be represented as
2Mg + O₂ → 2MgO

Question 17.
The electron dot diagram of magnesium oxide formation is given. Analyse the diagram and complete the table.

Answer:

Question 18.
Which are the ions present in magnesium oxide?
Answer:
Magnesium ion (Mg²⁺) and oxygen ion (O^2-).

Question 19.
How many electrons are transferred from magnesium to oxygen during the formation of magnesium oxide?
Answer:
Two electrons.
By the transfer of two electrons from magnesium to oxygen, an ionic bond is formed between them. The
compounds that are formed by ionic bonding are known as ionic compounds or electrovalent compounds.
The distribution of electrons of fluorine is given.

Question 20.
How many electrons are there in the outermost shell of fluorine?

Answer:
Seven electrons.

Question 21.
How many more electrons are required for one fluorine atom to attain octet configuration? 63caj
Answer:
One electron.

Question 22.
Is it possible to transfer electrons from one fluorine atom to another? If so, what, type of arrangement might have taken place, between the atoms in order to attain octet configuration?
Answer:
No, it is not possible to move electrons from one fluorine atom to another. In order to attain stability, atoms will share electrons.
In the case of some molecules like fluorine, the octet configuration is attained by the sharing of electrons.

Question 23.
Analyse the electron dot diagram of fluorine molecule formation through chemical bonding and answer the following questions.

(i) How many electrons are donated by each fluorine atom for sharing?
(ii) How many pairs of electrons are shared in the chemical bonding of fluorine molecule?
Answer:
(i) One each.
(ii) One pair.
The chemical bond formed as a result of the sharing of electrons between the combining atoms is called a covalent bond. The covalent bond formed by the sharing of one pair of electrons is a single bond.
A single bond is represented by a small line (-) between the symbols of the combining elements in molecules. The single bond in fluorine molecule can be represented using symbols such as F – F.

Question 24.
Oxygen is a diatomic molecule. Now answer the following questions.
(i) What is the atomic number of oxygen?
(ii) Write the electronic configuration of oxygen.
(iii) How many more electrons are required for one oxygen atom to attain the octet configuration?
Answer:
(i) Atomic number of oxygen is eight.
(ii) ₈O – 2, 6.
(iii) 2 more electrons.

Question 25.
The illustration of a chemical bond in an oxygen molecule is given below

How many pairs of electrons are shared in the oxygen molecule?
Answer:
Two pairs
The covalent bond formed by the sharing of two electron pairs or four electrons is called a double covalent bond.
The double bond in oxygen molecules can be represented by using symbols such as 0 = 0.

Question 26.
The illustration of a chemical bond in a nitrogen molecule is given below

How many pairs of electrons are shared here to complete the octet configuration?
Answer:
3 pairs
The covalent bond formed by the sharing of three electron pairs or six electrons is called a triple covalent bond.
The triple bond in nitrogen molecules can be represented by using symbols such as N ≡ N

Question 27.
Illustrate the chemical bond in a hydrogen molecule using an electron dot diagram.
Answer:

In this case, two hydrogen atoms share one pair of electrons, which forms a single bond. Stability is achieved by adopting the electronic configuration of helium, which is the nearest noble gas.

Formation of hydrogen chloride molecule:
The atomic number of hydrogen is 1.
Electronic configuration = 1.
The atomic number of chlorine is 17.
Electronic configuration = 2, 8, 7.
Chlorine needs one more electron to complete the octet, which the hydrogen atom will share, thereby forming the hydrogen chloride molecule. Hence, a single bond is present in hydrogen chloride.

Question 28.
Represent the covalent bond in hydrogen chloride using symbols.
Answer:
H – Cl

Question 29.
Depict the chemical bonding in hydrogen fluoride molecules.
Answer:

A water molecule consists of two hydrogen atoms and one oxygen atom. The chemical bonding present in water molecules can be represented as:

Question 30.
How many covalent bonds are formed here?
Answer:
2 covalent bonds.
Compounds formed by covalent bonding are called covalent compounds. When non-metals combine, usually covalent compounds are formed.

Question 31.
Is the shared pair of electrons in the HF molecule attracted equally by both atoms?
Answer:
No, the electrons are more attracted by fluorine.

Question 32.
Find out the electronegativity difference of the constituent elements and complete the table.

Compounds	Difference in electronegativity of constituent elements	Nature of the compound
Sodium chloride (NaCl)	3.16 – 0.93 = …………………	Ionic
Hydrogen Chloride (HCl)	3.16 – 2.20 = …………………	Covalent
Sodium Oxide (Na2O)	………………..	…………………
Calcium Chloride (CaCl2)	…………………	…………………
Methane (CH4)	…………………	…………………
Magnesium Fluoride (MgF2)	…………………	…………………

Answer:

Compounds	Difference in electronegativity of constituent elements	Nature of the compound
Sodium chloride (NaCl)	3.16 – 0.93 = 2.23	Ionic
Hydrogen Chloride (HCl)	3.16 – 2.20 = 0.96	Covalent
Sodium Oxide (Na2O)	3.44 – 0.93 = 2.51	Ionic
Calcium Chloride (CaCl2)	3.16 – 1.00 = 2.16	Ionic
Methane (CH4)	2.55 – 2.20 = 0.35	Covalent
Magnesium Fluoride (MgF2)	3.98 – 1.31 = 2.67	Ionic

Question 33.
Answer the questions given below
(i) What is the electronegativity value of hydrogen?
(ii) What is the electronegativity value of chlorine?
(iii) The nucleus of which of these atoms has a greater tendency to attract the shared pair of electrons involved in covalent bonding?
Answer:
(i) 2.20
(ii) 3.16
(iii) Chlorine will attract the shared pair of electrons.

Question 34.
Analyse the change in the electron arrangement in atoms during the formation of each compound and
Complete the table given below.

Answer:

Question 35.
Complete the following table regarding the combination of magnesium (Mg) and fluorine (F).

Element	Atomic number	Electron configuration	Number of electrons donated or accepted
Mg	12	–	–
F	9	–	–

Answer:

Element	Atomic number	Electron configuration	Number of electrons donated or accepted
Mg	12	2, 8, 2	2
F	9	2, 7	1

Question 36.
How many fluorine atoms are required to receive the electrons donated by magnesium?
Answer:
2 fluorine atoms.
During the formation of magnesium fluoride, one magnesium atom combines with two fluorine atoms. Hence, the chemical formula of magnesium fluoride will be MgF₂.

Question 37.
What are the constituent elements of aluminium oxide?
Answer:
Aluminium and Oxygen

Question 38.
What is the valency of aluminium? (Atomic number – 13)
Answer:
Electron configuration – 2, 8, 3
Therefore, the valency of aluminium is three.

Question 39.
What is the valency of oxygen? (Atomic number – 8)
Answer:
Electron configuration – 2, 6
Therefore, the valency of oxygen is two.

Question 40.
What are the constituent elements of carbon dioxide?
Answer:
Carbon and oxygen

Question 41.
Write the symbols of elements together, considering their electronegativity.
Answer:
C and O.

Question 42.
The valency of carbon is 4, and that of oxygen is 2. Interchange the valencies and write them as base indices.
Answer:

Chemical formula – C₂O₄
Divide the base indices by common factor, C_2/2O_4/2 = C₁O₂.
If the base index is 1, then there is no need to write. Therefore, the chemical formula of carbon dioxide is CO₂.

Question 43.
The constituent elements of some compounds and the valencies of their constituent elements are given in the following table. Find out the chemical formula.

Answer:

Question 44.
Which are the ions derived from hydrochloric acid? Why is it a monobasic acid?
Answer:
Hydrochloric acid contains H⁺ and Cl^–. The ionisation of one molecule of HC1 releases one H⁺ ion; hence, it is a monobasic acid.
In the case of sulphuric acid, two H⁺ and one SO₄^2- ions are released. Therefore, it is a dibasic acid. Hence, the chemical formula of sulphuric acid is H₂SO₄.

Question 45.
The basicity and the negative ions of certain acids are given in the table. Find their chemical formula and complete the table.

Answer:

Bases that are soluble in water are called alkalies. The number of OH” ions in an alkali will be equal to the number of positive ions.

Question 46.
Which is the positive ion present in sodium hydroxide?
Answer:
Sodium ion (Na⁺)

Question 47.
How many OH” ions, equal to the positive charge on sodium ion, will be present in sodium hydroxide?
Answer:
One

Question 48.
If so, what is the chemical formula of sodium hydroxide?
Answer:
NaOH

Question 49.
The positive ions of some bases are given in the table below. Find the chemical formulae and complete the table.

Answer:

Question 50.
Which is the positive ion in magnesium hydroxide, Mg(OH)₂?
Answer:
Magnesium ion (Mg²⁺).

Question 51.
Which is the negative ion in phosphoric acid, H₃PO₄?
Answer:
Phosphate ion (PO₄^3-).
Let us write the chemical formula of magnesium phosphate, which is formed from magnesium hydroxide and phosphoric acid.
Step 1 – Write the symbols of the ions Mg²⁺ + PO₄^3-
Step 2 – Interchange the number indicating charge and write as base indices. Mg₄(PO₄)₂
Therefore, the chemical formula of magnesium phosphate is Mg₃(PO₄)₂.

Question 52.
The reaction between sulphuric acid and calcium hydroxide forms salt calcium sulphate. To find the chemical formula of calcium sulphate, answer the following questions.
(i) Which is the positive ion in calcium hydroxide, Ca(OH)₂?
(ii) Which is the negative ion in sulphuric acid, H₂SO₄?
(iii) Write the symbol of the positive ion and then the symbol of the negative ion.
(iv) Write the number indicating the charge of each ion/radical as the base index after interchanging them.
Answer:
(i) Calcium ion, Ca²⁺
(ii) Sulphate ion, SO₄^2-
(iii) Ca²⁺ SO₄^2-
(iv) Ca₂(SO₄)₂
Simplify the base indices into simple whole number ratio
Ca_2/2(SO₄)_2/2 = CaSO₄
Therefore, the chemical formula of calcium sulphate is CaSO₄.

Question 53.
Certain positive ions and negative ions are given in the following’ table. Complete the table by writing the chemical formula and the name of the salt formed from these ions.

Answer: