Chapter 7 Chemical Bonding Textbook Solutions

NIOS Class 10 Science Chapter 7 Question Answers

INTEXT QUESTIONS 7.1

1. State the octet rule.

Ans: Every atom tends to attain 2 or 8e^– in its outermost shell to get stability like noble gases.

2. Why are noble gases non-reactive?

Ans: Because they have an inert gas configuration, which makes them very stable.

3. In the table given below, three elements and their atomic numbers are given. Which of them are stable and will not form compounds?

Element	At. No.	Stable/Unstable
ABC	103637

Ans: A and B

INTEXT QUESTIONS 7.2

1. Name the two types of ions present in NaCl.

Ans: Sodium ion Na⁺ and chloride ion Cl^–.

2. How many shells are present in Na⁺ ion?

Ans: Two (2)

3. What is the number of electrons present in Cl^– ion?

Ans: 18

4. Name the type of force of attraction present in ionic compounds.

Ans: Electrostatic force of attraction

5. In sodium chloride lattice, how many Cl^– ions surround each Na⁺ ion?

Ans: Six

6. Show the formation of Na₂O, CaCl₂ and MgO.

Ans:

7. Why is NaCl a bad conductor of electricity in solid state?

Ans: Due to the absence of free Na⁺ and Cl^– ions.

INTEXT QUESTIONS 7.3

1. How are covalent bonds formed?

Ans: A covalent bond is formed by the sharing of an equal no. of electrons between two atoms.

2. Show the formation of O₂, HCl, Cl₂ and N₂.

Ans:

3. How many covalent bond(s) is/are present in following compounds:

(i) H₂O (ii) HCl (iii) O₂ (iv) N₂

Ans:

(i) 2
(ii) 1
(iii) 2
(iv) 3

4. State loss or gain of electrons (giving their number) in the following changes :

(i) N ⎯→ N^3– (ii) Cl ⎯→ Cl^–

(iii) Cu ⎯→ Cu²⁺ (iv) Cr ⎯→ Cr³⁺

Ans:

(i) Gain of 3e^–
(ii) Gain of 1e^–
(iii) Loss of 2e^–
(iv) Loss of 3e^–

5. Why is ethyl alcohol is bad conductor of electricity in its aqueous solutions?

Ans: Ethyl alcohol does not produce H⁺ ions in its aqueous solution, hence it does not conduct electricity.

TERMINAL EXERCISE

1. Why ionic compounds conduct electricity in aqueous solution?

Ans: Ionic compounds conduct electricity in their molten state and in aqueous solutions. In aqueous solution, water is used as a solvent to dissolve ionic compounds. It weakens the electrostatic forces of attraction present among the ions. When these forces are weakened, the ions become free to move, hence they can conduct electricity.

2. Covalent compounds have low melting point than an ionic compound. Why?

Ans: As the forces of attraction between the molecules are weak in nature, a small amount of energy is sufficient to overcome them. Hence, the melting points and boiling points of covalent compounds are lower than those of ionic compounds.

3. Explain the formation of Na⁺ ion from Na atom.

Ans: Na atom is the element which is not involved in any bond. The electronic configuration of Sodium with an atomic number of 11 is 2,8,1. It has one electron in its outermost shell (M). If it loses this electron, it is left with 10 electrons and becomes positively charged. The cation in this case is called the sodium cation, Na+.

4. How would you explain the bonding in MgCl₂?

Ans: Magnesium has an atomic number 12 with an electronic configuration of 2,8,2. It can attain a stable configuration if it loses the 2 electrons on its outermost shell. Chlorine, on the other hand has an electronic configuration of 2,8,7. It requires just one electron to attain stability.

Magnesium requires two electrons, thereby bonding with 2 Chlorine atoms to attain its stability. Magnesium loses its two electrons, which the chlorine atoms receive to form MgCl₂.

Mg —→ Mg²⁺ + 2e^–

2Cl(g) + 2e^– —→ 2Cl^–(g)

Mg + 2Cl —→ MgCl₂

5. Which of the following statements are correct for ionic compounds:

(i) They are insoluble in water.

(ii) They are neutral in nature.

(iii) They have high melting points.

Ans: Statements (ii) and (iii) are correct.

6. State three characteristic properties of ionic compounds.

Ans:

The ionic compounds are hard and brittle in nature.
They have high melting and boiling points.
They conduct electricity in their molten state and in aqueous solutions.

7. How does a covalent bond form?

Ans: The covalent bond forms when the forces of attraction and repulsion balance each other, and the

potential energy is minimum. It is this lowering of energy that leads to the formation of the covalent bond.

8. What is the number of colvent bonds present in the following molecules?

(i) Cl₂ (ii) N₂ (iii) O₂ (iv) H₂

Ans:

(i) Cl₂: Single
(ii) N₂: Triple
(iii) O₂: Double
(iv) H₂: Single

9. Classify the following statements as true or false:

(i) Ionic compounds contain ions which are held together by weak electrostatic forces.

(ii) Ionic compounds have high melting and boiling points.

(iii) Covalent compounds are good conductors of electricity.

(iv) Solid sodium chloride is a good conductor of electricity.

Ans:

(i) False
(ii) True
(iii) False
(iv) False

10. Classify the following compounds as ionic or covalent:

(i) sodium chloride (ii) calcium chloride (iii) oxygen

(iv) hydrogen chloride (v) magnesium oxide (vi) nitrogen

Ans:

(i) Sodium chloride – NaCl: Ionic
(ii) Calcium chloride – CaCl₂: Ionic
(iii) Oxygen – O₂: Covalent
(iv) Hydrogen chloride – HCl: Covalent
(v) Magnesium oxide – MgO: Ionic
(vi) Nitrogen – N₂: Covalent

11. An element ‘X’ has atomic no. 11 and ‘Y’ has atomic no. 8. What type of bond will they form? Write the formula of the compound formed by reacting X and Y.

Ans:

Element X with atomic number 11 – 2,8,1

Element Y with atomic number 8 – 2, 6

Since element Y requires two electrons, there will be two atoms of element X. Therefore, the ionic bond between these elements will lead to the formation of X₂Y.

12. Name the type of bonds present in H₂O molecule.

Ans: There are two covalent bonds in the H₂O molecule. One covalent bond between the oxygen molecule and each hydrogen atom.