Samacheer Kalvi 9th Term II Science Book Back Question and Answers – Unit 5:

Samacheer Kalvi 9th Standard New Science Book Back 1 Mark and 2 Mark Question & Answers PDF uploaded and available below. Class 9 New Syllabus 2021 to 2022 Book Back Question & Answer solutions available for both English and Tamil Medium. Class 9 Science Book Term 2 Unit 5 – Chemical bonding Answers/Solutions are provided on this page. 9th Std Science Book is of Term 1st, 2nd, 3rd, and consists of 9 Units in each Term. All 9 Units of Term 1st, 2nd, 3rd Science Book Back One, and Two Mark Solutions are given below.

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Samacheer Kalvi 9th Science Book Back Unit 5 Term 2 Solutions Guide PDF:

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Term – 2

Unit – 5

Chemical bonding

I. Choose the correct answer:

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

2. Sodium having atomic number 11, ready to ___________________ electron/ electrons to attain the nearest Noble gas electronic configuration.
a) gain one
b) gain two
c) lose one
d) lose two

3. Atoms having 1,2 or 3 electrons in its valence shell will readily form ________
a) cation
b) anion

4. The element that would form anion by gaining electrons in a chemical reaction is _______________
a) Potassium
b) Calcium
c) Fluorine
d) Iron

5. Bond formed between a metal and non metal atom is usually __________
a) ionic bond
b) covalent bond
c) coordinate bond

6. ______________ compounds have high melting and boiling points.
a) Covalent
b) Coordinate
c) Ionic

7. Covalent bond is formed by __________
a) transfer of electrons
b) sharing of electrons
c) sharing a pair of electrons

8. Oxidising agents are also called as ___________ because they remove electrons form other substances.
a) electron donors
b) electron acceptors

9. Elements with stable electronic configurations have eight electrons in their valence shell. They are ___
a) Halogens
b) Metals
c) Noble gases
d) non metals

II. Answer in brief

1. How do atoms attain Noble gas electronic configuration.

• 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. By losing one electron sodium atom attains the electronic configuration of neon.
• 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. By gaining one electron chlorine attains the electronic configuration of argon.

2. CCl4 is insoluble in water but NaCl is soluble in water. Give reason.

• Covalent compounds are not soluble in water. As CCI₄ is a covalent compound it does not dissolve in polar solvent water.
• Ionic compounds are soluble in water. As NaCI is an ionic compound it dissolves in water.

3. Explain Octet rule with an example.

• 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 lose one electron to attain Neon’s stable electronic configuration. Similarly, chlorine has electronic configuration 2,8,7. To attain the nearest noble gas (i.e. argon) configuration, it needs one more electron. So chlorine readily gains one electron from other atom and attains stable electronic configuration. Thus elements tend to have stable valence shell (eight electrons) either by losing or gaining electrons.

4. Write a note on different types on bonds?

• Ionic / Electrovalent Bond – Bond formed between cation and anion because of the transfer of electrons from one atom to other atom
• Covalent bond                    –    Bond formed between atoms by the mutual sharing of electrons.
• Coordinate covalent Bond – Bond formed between atoms by mutual sharing of electrons which are supplied by one atom.

5.  Find the odd one out

a) H₂, CI₂, NaCI, O₂, N₂ = N₂
NaCI is ionic compound but the others are covalent compounds.

b) H₂O₂, MnO₄, LiAIH₄, Cr₂O₇^2- = KiAIH₄
LiAIH₄ is a reducing agent but the others are oxidizing agents.

6. Correct the wrong
a)Ionic compounds dissolve in non polar
Ionic compounds dissolve in polar solvents.

b) Covalent compounds conduct electricity in molten or solution
Covalent compounds do not conduct electricity in molten or solution state.

7. Complete the table given below

Ans:

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

9. 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:

10. Choose the correct answer from the choices given below:

The property which is characteristics of an Ionic compound is that
a) It often exists as gas at room
b) It is hard and brittle.
c) It undergoes molecular reactions
d) It has low melting

11. Identify the following reactions as oxidation or reduction.
a) Na à Na⁺ + e^– = oxidation
b) Fe³⁺ + 2e^– àFe⁺ = reduction

12. Identify the compounds as Ionic/Covalent/ Coordinate based on the given characteristics.
a) Soluble in non polar solvents  – covalent
b) Undergoes faster/instantaneous reactions – Ionic
c) Non conductors of electricity – Coordinate
d) Solids at room temperature – Ionic

14. Considering MgCI₂ as ionic compound and CH₄ as covalent compound give any two differences between these two compounds.
i) MgCI₂ is an ionic compound where as CH₄ is a covalent
ii) In MgCI₂ the electrostatic force between Mg²⁺ and CI is But the force is weak between carbon and hydrogen atoms in CH₄.

15. Why are Nobel gases inert in nature?
Noble gases have stable electronic configuration. The outer shell in them has 8 electrons (except Helium). So they need not lose or gain electrons. As a result they remain inactive and stable.

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