Chemical Bonding Class 9 Extra Questions and Answers Kerala Syllabus Chemistry Chapter 3

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

Question 1.
What peculiarity do you see in the electronic configuration of noble elements except Helium?
Answer:
Except Helium all other elements have 8 electrons in the outermost shell, hence shall be considered to be chemically stable.

Question 2.
What is called an octet electron configuration?
Answer:
The arrangement of eight electrons in the outermost shell of an atom is called octet electron configuration.

Question 3.
Why helium is stable?
Answer:
In the Helium atom, there is only one shell. The maximum number of electrons in the first shell is 2. Hence, the electron pattern system of Helium is also stable.

Question 4.
The electronic configuration of some elements is given below.

Element	Atomic mass	Electronic configuration
Magnesium	12	2, 8, 2
Oxygen	8	2, 6
Sodium	11	2, 8, 1
Chlorine	17	2, 8, 7

(i) You are familiar with the compounds of these elements. Write the names of some compounds.
(ii) How are atoms in these compounds held together?
Answer:
(i) Magnesium chloride, Sodium oxide, Sodium chloride, Magnesium oxide.
(ii) Strong, attractive force holds these atoms together in a compound.

Question 5.
What is meant by Chemical Bonding?
Answer:
The attractive force that holds the atoms together in the formation of a molecule is called chemical bonding.

Question 6.
How many electrons are there in the outermost shell of sodium atom?
Answer:
Only one electron.

Question 7.
How the ionic bond formation of sodium oxide is represented? [Hint: Atomic No. of sodium 11, oxygen 8]
Answer:
Sodium oxide is Na₂O.

Question 8.
In the formation of sodium chloride which atoms are combining?
Answer:
Sodium, chlorine

Question 9.
How many electrons are there in outermost shell of chlorine?
Answer:
7

Question 10.
How do chlorine and sodium attain stability?
Answer:
Sodium donates one electron to chlorine to become a sodium ion [Na⁺], and chlorine gains one electron to become a chloride ion [Cl^–].

Question 11.
Draw the electron dot diagram of the transference of electrons of a sodium atom and chlorine atom in the formation of a sodium chloride molecule.
Answer:

Question 12.
Explain about the electron transfer during the formation of sodium chloride.
Answer:
During the formation of sodium chloride sodium atom donates an electron and gets converted to a sodium ion (Na⁺). Chlorine accepts an electron to form a chloride ion (Cl^–). Through this, sodium and chlorine atoms complete an octet in their outermost shell to attain stability. The electrostatic force of attraction holds together the oppositely charged ions thus formed. This attractive force is called the Ionic Bond.

Question 13.
Define Ionic Bond?
Answer:
An ionic bond is a chemical bond formed by electron transfer. In an ionic bond, the ions are held together by the electrostatic force of attraction between the oppositely charged ions.

Question 14.
Draw the electron dot diagram of the following compounds.
A) Sodium Fluoride and
B) Magnesium Fluoride [Hint: Atomic No. Na = 11, F = 9, Mg = 12].
Answer:

The distribution of electrons of fluorine is given.

Question 15.
What happens during the formation of fluorine molecule, electron transfer or electron sharing?
Answer:
Electron sharing

Question 16.
How covalent bonds are formed?
Answer:
The chemical bond formed as a result of the sharing of electrons between the combining atoms is called a covalent bond.

Question 17.
How single bonds are formed?
Answer:
Single bonds are formed by sharing one pair of electrons. A small line between the symbols of the combining elements represents it. For example, the Fluorine molecule can be represented as F – F.

Question 18.
Draw the electron dot diagram of the formation of a chlorine, molecule by combining two chlorine atoms.
Answer:

Chlorine atoms share one pair of electrons, forming a single covalent bond.

Question 19.
Complete the table given below related to covalent bonding.

Element molecule	Shared electron pairs	Chemical bond
F2	One pair	Single bond
Cl2	—	—
O2	—	—
N2	—	—

Answer:

Element molecule	Shared electron pairs	Chemical bond
F2	One pair	Single bond
Cl2	One pair	Single bond
O2	Two pair	Double bond
N2	Three pair	Triple bond

Question 20.
Examples of some covalent compounds are given. Draw the chemical bonds of the compounds using an electron dot diagram.
a) CH₄
b) HF
C) H₂O
Answer:

Question 21.
Who proposed the electronegativity scale?
Answer:
Linus Pauling

Question 22.
Explain the properties of ionic compounds and covalent compounds.
Answer:

Ionic compounds	Covalent compounds
Generally solids.	Either solid, liquid or gas
Soluble in water	Insoluble in water. But soluble in organic solvents like kerosene, benzene etc.
Conduct electricity in a fused or solution state.	Do not conduct electricity.
High melting and boiling point	Low melting and boiling point.

Question 23.
In the formation of magnesium oxide, how many electrons are donated by magnesium?
Answer:
Two electrons

Question 24.
What is the valency of oxygen? ood&cnJlsaanjj cuaejorSmfl o^)t«nauo6nf?
Answer:
Two

Question 25.
Write down the formulae of
(i) Sodium oxide
(ii) Aluminium chloride
(iii) Sodium sulphide
(iv) Magnesium hydroxide
Answer:

Question 26.
Write down the names of compounds represented by the following formulae:
(i) Al₂(SO₄)₃
(ii) CaCl₂
(iii) K₂SO₄
(iv) KNO₃
(v) CaCO₃
Answer:
(i) Aluminium sulphate [Al₂(SO₄)₃]
(ii) Calcium chloride [CaCl₂]
(iii) Potassium sulphate [K₂SO₄]
(iv) Potassium nitrate [KNO₃]
(v) Calcium carbonate [CaCO₃]

Question 27.
Give the names of the elements present in the following compounds.
(a) Quick lime
(b) Hydrogen bromide
(c) Baking powder
(d) Potassium sulphate.
Answer:
(a) Quick lime is calcium oxide (CaO) – Ca and O
(b) Hydrogen bromide (HBr) – H and Br
(c) Baking powder (NaHCO₃) – Na, H, C and O
(d) Potassium sulphate (K₂SO₄) – K, S and O

Question 28.
Which of the following represents a correct chemical formula? Name it.
a) CaCl
b) BiPO₄
c) NaSO
d) NaS
Answer:
b) BiPO₄ – Bismuth phosphate
The correct formulas for other compounds are,
Calcium chloride – CaCl₂, Sodium sulphate – Na₂SO₄, Sodium sulphide – Na₂S.

Question 29.
Which type of force holds the atoms together in an ionic compound?
Answer:
Electrostatic force of attraction of oppositely charged ions.

Question 30.
The formation of sodium fluoride molecule is represented below.

Identify the type of bonding in this molecule.
Answer:
Ionic bonding

Question 31.
Electronic configuration of magnesium is 2, 8, 2. What is the valency of magnesium?
Answer:
Two.

Question 32.
Which type of force holds the atoms together in an ionic compound?
Answer:
Electrostatic force of attraction of oppositely charged ions.

Question 33.
Find the odd one out. [Ar, Ne, Kr, He]
Answer:
He (Duplet configuration)

Question 34.
Draw the electron dot structure of H₂S.
Answer:

Question 35.
Which is the anion of sodium sulphate?
Answer:
Sulphate (SO₄^2-) is the anion.

Question 36.
Which noble gas has no octet arrangement in the outermost shell of the atom?
Answer:
Helium (He)

Question 37.
The force that binds together constituent particles of a molecule is ………………….
Answer:
Chemical bonding

Question 38.
What change in energy takes place when a molecule is formed from its atoms?
Answer:
Energy decreases

Question 39.
Some elements and their electronic configuration are given in the table. (Hint: Symbols are not real).

Element	Electronic configuration
A	2, 8, 1
B	2, 8
C	2, 8, 7

a) Among these elements, which has the highest stability? Give reason.
Answer:
a) B
Reason: Element B has 8 electrons in the outermost shell. (Octet rule)

Question 40.
From the following statements, write those applicable to ionic compounds.
a) Usually do not dissolve in water.
b) Conduct electricity in the molten state and aqueous solution.
c) Generally not a conductor of electricity.
d) Exists in the solid state.
Answer:
b) Conduct electricity in a molten state and aqueous solution
d) Exists in a solid state.

Question 41.
Identify the relation and fill up the blank
(i) Electron dot diagram: Gilbert Newton Lewis
Electronegativity scale: ……………………..
(ii) Elements : Symbols
Compounds : ………………….
Answer:
(i) Electronegativity scale – Linus Pauling
(ii) Compounds: Chemical formula

Question 42.
Analyse the electronic configurations of the elements given below and answer the following questions, (symbols are not real).
p – 2, 7
Q – 2, 8, 2
R – 2, 8, 8
a. R is the most stable element. Why?
b. Which one of these elements donates its electrons in chemical reactions?
Answer:
a) Because of the octet electron configuration. (The arrangement of 8 electrons in the outermost shell).
b) Q

Question 43.
How many atoms are present in a (i) H₂S molecule and (ii) PO₄^3- ion?
Answer:
(i) H₂S
2 Hydrogen atoms + 1 sulphur atom = 3 atoms
(ii) PO₄^3-
1 phosphorous atoms + 4 oxygen atoms = 5 atoms.

Question 44.
In NaCl, sodium and chlorine are held together by the attraction between anions and cations in it. Identify the anion and cation in the NaCl molecule.
Answer:
Anion Cl^–
Cation Na⁺

Question 45.
Choose the compounds containing ionic bonds and covalent bonds out of the following.
HCl, NaCl, MgO, CH₄, CCl₄, MgCl₂
Answer:
Ionic bond – NaCl, MgO, MgCl₂ Covalent bond – HCl, ₄, CCl₄

Question 46.
The electronic configuration of oxygen is 2, 6.
a) Oxygen usually shows valency 2. What is the reason?
b) Illustrate the formation of sodium oxide using an electron-dot diagram.
(Hint: Electronic configuration of Na = 2, 8, 1)
Answer:
a) Oxygen has 6 electrons in the outermost shell. Thus, it tends to accept 2 electrons to attain stability. This usually shows valency 2.
b)

Question 47.
MgF₂ is an ionic compound. [Hint: Atomic number of Mg = 12, F = 9]
a) Which is the cation present in MgF₂?
b) Write the electronic configuration of the anion in this compound.
c) Write one property of ionic compounds.
Answer:
a) Magnesium ion – Mg²⁺
b) Anion is F^–.
Electronic configuration – 2, 8.
c) They are good conductors of electricity in a molten and aqueous state.

Question 48.
What are ionic and molecular compounds? Give examples.
Answer:

• Ionic compounds are made up of ions.
• Ionic compounds have strong electrostatic forces of attraction, called ionic bonds or electrovalent bonds, that hold cations and anions together.
• Examples are Sodium chloride, calcium oxide, etc.
• In molecular compounds, element atoms share electrons via covalent connections.
• Examples include methane (CH₄) and water (H₂O).

Question 49.
The electron dot diagram of the formation of sodium oxide is given below

(Hint: Atomic number Na = 11 and O = 8)
a) Which atom donates an electron in this reaction?
b) Write the electronic configuration of the oxide ion (O2 ).
c) Write the name of the cation.
d) Which type of chemical bonding is present in sodium oxide?
Answer:
a) Sodium (Na)
b) 2, 8
b) Sodium ion
c) Ionic bonding

Question 50.
The electron dot diagram of magnesium oxide is given below.
a) Which atom accepts electrons?

b) Write the equation showing the formation of Mg²⁺ ions.
c) Name the anion present in it.
d) Write the electronic configuration of the Mg²⁺ ion.
Answer:
a) Oxygen (O)
b) Mg → Mg²⁺ + 2e^–
c) Oxide ion (O^2-)
d) 2, 8

Question 51.
a) Why noble gases do not take part in chemical reactions?
b) Noble gas helium doesn’t have an octet electron configuration in the outermost shell. Yet, it is stable. Why?
Answer:
a) Noble gases do not take part in chemical reactions because they have attained stable octet electron configuration (except helium) in the outermost shell. So, they are chemically stable, b) Helium atom has only one shell (K) in it. The maximum number of electrons that can be accommodated in the first K shell is 2. Helium has 2 electrons in it. So it is stable.

Question 52.
Which among the following is a molecule showing a polar nature?
(H₂, HBr, N₂, Cl₂)
Answer:
HBr

Question 53.
Nitrogen (N₂) molecule doesn’t show polar nature. Why?
Answer:
It is a homodiatomic molecule in which the two atoms have the same electronegativity values.

Question 54.
Write the chemical formula of sodium sulphide.
Answer:
Sodium – 1
Sulphide – 2
Formula – Na₂S

Question 55.
How many pairs of electrons are mutually shared in the formation of a nitrogen molecule?
Answer:
3 pairs

Question 56.
Write the chemical formula of the salt formed by the reaction of ammonium ion and sulphate ion.
Answer:
(NH₄)₂SO₄ (Ammonium sulphate)

Question 57.
Write down the name of the compound represented by the formula KNO₃.
Answer:
Potassium nitrate

Question 58.
What is meant by the term chemical formula?
Answer:
A chemical formula is the most concise method of representing a compound using symbols and the valency of elements.

Question 59.
The chemical formula of calcium carbonate is CaCO₃ then what is the valency of Ca?
Answer:
The valency of calcium is 2.

Question 60.
The formula of a compound is X₃Y. The valencies of elements X and Y will be, _________ respectively
Answer:
Valency of X – 1
Valency of Y – 3

Question 61.
Magnesium ion (Mg²⁺) and Phosphate ion (PO₄^3-) combine to form magnesium phosphate.
a) Identify the cation in magnesium phosphate.
b) Write the chemical formula of magnesium phosphate.
Answer:
a) Magnesium ion (Mg²⁺)
b) Mg₃(PO₄₂)

Question 62.
Write the chemical formula of baking soda and caustic soda.
Answer:
Baking soda is the common name used for sodium hydrogen carbonate, and caustic soda is the name for sodium hydroxide.
Baking soda – NaHCO₃
Caustic soda – NaOH

Question 63.
Some elements and their valencies are given.

Element	Valency
Ba	2
Cl	1
O	2

a) Write the chemical formula of Barium chloride.
b) The chemical formula of Calcium oxide is CaO. What is the valency of Ca?
Answer:
a)BaCl₂
b) The valency of calcium is 2.

Question 64.
Identify the Ionic and Covalent compounds from the following.
a) CaO
b) CO₂
[Hint: Electronegativity values of O = 3.44, C = 2.5, Ca = 1.0]
Answer:
a) CaO is an ionic compound (3.44 – 1.0 = 2.44)
2.44 >1.7; hence, ionic bonding is present in it.

b) CO₂ is a covalent compound (3.44 – 2 .5 = 0.94)
0.94 < 1.7; hence, covalent bonding is present in it.

Question 65.
The element ‘X’ forms a diatomic molecule with a double bond.
a) How many electrons are there in the outermost shell of ‘X’?
b) How many pairs of electrons are shared for this bond formation?
Answer:
a) a) 6
b) Two pair

Question 66.
Some elements and their electronic configuration are given below. (Symbols are not real)

Element	Electronic configuration
A	2, 8, 7
B	2, 6
C	2, 8, 2
D	2, 5

a) Which among the elements shows the same valency?
b) Write the chemical formula of the compound formed by the combination of C and A.
Answer:
a) B and C (Valency 2)
b) CA₂

Question 67.
Electronic configuration of Nitrogen is 2, 5.
a) How many electrons are required by nitrogen to attain octet electronic configuration?
b) Draw the electron dot diagram of the formation of nitrogen (N₂) molecules.
Answer:
a) 3
b)

Question 68.
The atomic numbers of the elements X and Y are 13 and 16, respectively.
a) Write the electronic configuration of X and Y
b) Write the valency of X and Y
c) Write the molecular formula of the compound formed by the combination of X and Y.
Answer:
a) ₁₃X = 2, 8, 3
Y = 2, 8, 6
b) Valency of X = 3
Valency of Y = 2
c) X₂Y₃

Question 69.
Electronegativity values of some elements are given.
H = 2.20
O = 3.44
Mg = 1.31
On the basis of electronegativity values, identify the type of chemical bond in H₂O and MgO. Give reasons.
Answer:
If the electronegativity difference is greater than 1.7, the compound is ionic, and if it is less than 1.7, the compound is covalent.

Question 70.
a) Draw the electron dot diagram of the formation of hydrogen chloride (HCl) molecule. [Hint: Electronic configuration H – 1, Cl -2, 8, 7]
b) The HCl molecule shows a polar nature. Why?
Answer:
a)

b) HCl is a polar molecule. This is because the Chlorine (Cl) atom in the HCl molecule is more electronegative and does not share the bonding electrons equally with Hydrogen (H).

Question 71.
Analyse the given electron dot diagram and answer the following questions.

a) Which type of chemical bond is represented here?
b) What is the valency of Chlorine in this compound?
c) Write the chemical formula of Aluminium chloride (Hint: Valency of Aluminium = 3)
Answer:
a) Covalent Bond
b) One
c) Valency of Al = 3 Valency of Cl = 1
Chemical formula = AlCl₃

Question 72.
Electronegativity values of some elements are given. Analyse these values and answer the following questions. [Electro negativity of S = 2.58,03.44, Ca 1.0, F = 3.98]
a) Complete the table

Compound	Type of bond
SO2	A
CaF2	B

b) Justify your answer.
Answer:
a)

Compound	Type of bond
SO2	Covalent
CaF2	Ionic

b) If the difference in electronegativity values of elements in a compound is 1.7 or more compound shows ionic character, and if it is less than 1.7 compound shows a covalent nature. For SO₂
Difference = 3.44 – 2.58 = 0.86
For CaF₂
Difference = 3.98 – 1.0 = 2.98

Question 73.
Carbon combines with chlorine to form a compound carbon tetrachloride. [Hint: Atomic Number: C = 6, Cl = 17]
a) How many electrons are required to complete the octet of a carbon atom?
b) How many atoms of chlorine should combine with a carbon atom to complete the octet?
c) Which type of covalent bond is present in carbon tetrachloride? (Single bond, Double bond, Triple bond)
Answer:
a) 4
b) 4
c) Single bond

Question 74.
The molecular formula of Carbon tetrachloride is CCl₄
[Hint: Electronegativity C = 2.55 and CI = 3.16; Atomic number C =6 and CI = 17]
a) How many electrons are present in the outermost shell of carbon?
b) Which type of chemical bonding is present in CCl₄?
c) Draw the electron dot diagram of the formation of CCl₄.
Answer:
a) 4
b) Covalent bonding (single bond)
C – 2.55
Cl – 3.16
Electronegativity difference = 3.16 – 2.55 = 0.61 <1.7

Thus, covalent bonding.
c)

Question 75.
Oxygen molecule (O₂) and Nitrogen molecule (N₂) are formed by covalent bonding.
a) Which type of covalent bond is formed in N₂ molecule.?
b) How many pairs of electrons are shared in the O₂ molecule?
c) Draw the electron dot diagram illustrating the formation of chemical bonds in the O₂ molecule [Hint: Atomic number of O = 8, N = 7]
Answer:
a) Triple bond
b) 2 pair
c)

Question 76.
The table lists the valencies of different elements.

Symbol of element/ion	Valency
O	2
Na	1
OH	1

a) What will be the chemical formula of sodium oxide?
b) How many oxygen atoms are there in 2Fe₂O₃?
c) How many atoms are there in H₂SO₄?
d) Write the chemical formula of sodium hydroxide,
Answer:
a) Na₂O
b) 6 oxygen atoms
c) 2H + 1 S + 40 = 7
d) NaOH is the chemical formula of sodium hydroxide.