NIOS Class 10 Chapter 7 Chemical Bonding Questions Answers

This chapter is from Module 2 Matter in Our Surroundings Class 10 Science and Technology (212). This post provides you complete answer of all intext and terminal questions with a complete explanation with diagrams.

Our experienced teachers have provided easy and accurate answers to all questions that will help you complete your assignments.

Chemical Bonding - Overview

In this lesson   form NIOS class 10 Science, students will gain the knowledge about chemical bond and types, properties of ionic compounds, properties of covalent compounds.

 

Intext Questions 7.1 with Answers

Q1. State octet rule.

Answer

Atoms have tendency to have eight electrons in their outermost or valence shell (He has 2 electrons in outermost shell) to achieve stable electronic configuration.

Example:

 Sodium loses one electron to achieve 8 electrons in the next lower shell.

 

Q2. Why noble gases are non-reactive?

Answer

Noble gases have completely filled outermost shell so they do not gain, lose or share electrons that’s why their chemical reactivity is almost low under normal conditions. So, they are non- reactive.

 

 

Q3. In the table given below three elements and their atomic numbers are given. which of them are stable and will not form compound?

 

Element	Atomic No.	Stable/unstable
A	10
B	36
C	37

Answer

Element	Atomic No.	Element	Stable/unstable	Compound formation
A	10	Ne	Stable	No
B	36	Kr	Stable	No
C	37	Rb	Unstable	Yes

 

 

Intext Questions 7.2 with Answers

 

Q1. Name the two types of ions present in NaCl.

Answer

NaCl has Sodium (Na⁺ ) and chloride (Cl^-) ions.

 

Q2. How many shells are present in Na⁺ ion?

Answer

Sodium ion has 2 shells (K,L)

 

Q3. What is the number of electrons present in Cl^- ion?

Answer

Chloride ions has 18 electrons.

 

Q4. Name the type of force of attraction presents in ionic compounds.

Answer

Electrostatic force of attraction between cations and anions.

 

Q5. In sodium chloride lattice, how many Cl^- ions surround each Na⁺ ion?

Answer

In sodium chloride lattice, 6 chloride ions surround each Na⁺ ion.

 

Q6. Show the formation of Na₂O, CaCl₂ and MgO.

Answer

 

 

Q7. Why NaCl is bad conductor of electricity in solid state?

Answer

NaCl is bad conductor of electricity in solid state because Na⁺  and Cl^- ions are fixed in crystal lattice in solid state so these ions do not move freely and electric current requires free moving ions.

 

Intext Questions 7.3 with Answers

Q1. How covalent bonds are formed?

Answer

When two atoms of same element or different element share one or more electrons to achieve stable electronic configuration, the bond formed between atoms is called covalent bond.

Example

H₂ molecule: Each hydrogen atom shares 1 electron form single covalent bond.

 

 

Q2. Show the formation of O₂, HCl, Cl₂ and N₂.

Answer

Q3. How many covalent bond(s) is/are present in following compounds:

(i)        H₂O 

(ii) HCl 

(iii) O₂ 

(iv) N₂

Answer

Compound	Bonds	Number of shared pairs
H2O	2 single bonds(O-H)	2 shared pairs
HCl	1 single bond (H-Cl)	1 shared pair
O2	1 double bond (O=O)	2 shared pairs
N2	1 triple bond    (N≡N)	3 shared pairs

Q4. 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⁺

Answer

(i)                   N→ N^3-

A neutral nitrogen atom has 5 valence electrons and it gains 3 electrons to complete its octet.

(ii)               Cl →Cl^-

A neutral chlorine atom has 7 valence electrons and it gains 1 electron to complete its octet.

(iii)            Cu →Cu²⁺

A neutral copper atom loses 2 electrons to form copper cation.

(iv)             Cr →Cr³⁺

A chromium atom loses 3 electrons to form chromium cation.

 

 

Q5 Why ethyl alcohol is bad conductor of electricity in its aqueous solutions?

Answer

Ethyl alcohol is a covalent compound and does not dissociate into ions in aqueous solution. Free ions are essential for conductivity of electricity.

 

Terminal Exercise Questions with Answers

Q1. Why ionic compounds conduct electricity in aqueous solution?

Answer

When ionic compounds are dissolved in water. Since water is a polar solvent, it weakens the electrostatic forces of attraction among ions. So ionic compound dissociates into cation and anions which conduct electricity.

That’s why ionic compounds conduct electricity in molten state or in aqueous solutions.

 

NaCl + H₂O  → Na⁺_(aq)  + Cl^-_(aq)

 

Q2. Covalent compounds have low melting point than an ionic compounds why?

Answer

Covalent compounds have low melting points because the forces of attraction between molecules is weak so a small amount of energy is required to break these weak intermolecular forces.

Example: Naphthalene is a covalent compound has melting point 353K.

 On the other hand, ionic compounds have very high melting points due to strong electrostatic forces of attraction between oppositely charged ions. So large amount of energy is required to break this force.

Example: NaCl has melting point 1074K

 

 

Q3. Explain the formation of Na⁺ ion from Na atom.

Answer

Sodium atom (Na) has atomic number 11 so its electronic configuration is 1s² 2s² 2p⁶ 3s¹

Sodium has 1 electron in the outermost shell so sodium loses 1 electron this valence electron from the outermost shell to achieve stable configuration (nearest to noble gas).

Na →Na⁺ + e^-

Now after losing one electron, sodium atom (Na) becomes sodium ion (Na⁺) and its electronic configuration is 1s² 2s² 2p⁶ which is stable octet.

 

Q4. How would you explain the bonding in MgCl₂?

Answer

Magnesium chloride is an ionic compound which has magnesium and chlorine.

 Magnesium has atomic number 12 so it has 12 protons and 12 electrons. Its electronic configuration is 2,8,2.

Chlorine has atomic number 17. So it has 17 protons and 17electrons. Its electronic configuration is 2,8,7.

Formation of Magnesium ion

Magnesium has 2 valence electrons so it loses these two electrons to achieve the stable configuration of 2,8 and becomes magnesium cation (Mg²⁺).

Mg →Mg²⁺  + 2e^-

Formation of Chloride ion

The two electrons lost by magnesium are gained one each by two chlorine atoms and two chloride ions are formed.

Cl₂ + 2e^-   → 2Cl^-

Formation of Magnesium Chloride

Now one magnesium ion combines with two chloride ions to form magnesium chloride (Ionic compound). MgCl₂ has ionic bond formed by exchange of electrons.

Q5. Which of the following statements are correct for ionic compounds:

(i)    They are insoluble in water.

(ii)  They are neutral in nature.

(iii)    Thy have high melting points.

Answer

(i)       They are insoluble in water. - Incorrect

(ii)    They are neutral in nature. – Correct

(iii)    Thy have high melting points. – Correct

 

 

Q6. State three characteristics properties of ionic compounds.

Answer

Ionic compounds have following characteristics:

    1.  High melting and boiling points: Ionic compounds have high electrostatic forces of attraction present between the opposite ions so a lot of thermal energy is required to overcome these forces. Example: NaCl has melting point 1074K and boiling point 1686K.

    2. Electrical conductivity: Ionic compounds conduct electricity in molten state and in aqueous solution. Ionic compounds dissociate into free ions in the molten state and in aqueous solution so they carry electricity.

    3. Solubility: Ionic compounds are soluble in polar solvent like water.

 

Q7. How does a covalent bond form?

Answer

Covalent bond is formed when two atoms share one or more pairs of electrons to achieve stable electronic configuration.

This bond forms when the forces of attraction and repulsion balance each other and the potential energy is minimum.

The following types of covalent bonds are formed:

    1. Single covalent bond: When one pair of electrons is shared.

    2. Double covalent bond: When two pairs of electrons are shared.

    3. Triple covalent bond: When three pairs of electrons are shared.

Example:

H₂ molecule: Each hydrogen atom shares 1 electron.

O₂ molecule: Each oxygen atom shares 2 electrons.

N₂ molecule : Each nitrogen atom shares 3 electrons.

 

Q8. What is the number of colvent bonds present in the following molecules?

(i)           Cl₂   (ii) N₂  (iii) O₂  (iv) H₂

Answer

(i)      Cl₂:  Each chlorine atom shares 1 electron so single bond is present.

(ii)   N₂:  Each nitrogen atom shares 3 electrons so triple bond is present.

(iii)    O₂: Each oxygen atom shares 2 electrons so double bond is present.

(iv)   H₂: Each hydrogen atom shares 1 electrons so single bond is present.

 

Q9. Classify the following statements as true or false:

(i)    Ionic compounds contain ions which are held together by weak electro-static forces.

(ii)   Ionic compounds have high melting points.

(iii)    Covalent compounds are good conductors of electricity.

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

Answer

(i)   Ionic compounds contain ions which are held together by weak electro-static forces. – False

(ii)  Ionic compounds have high melting points. - True

(iii) Covalent compounds are good conductors of electricity. - False

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

 

Q10. Classify the following compounds as ionic  or covalent:

(i)    Sodium chloride

(ii)    Calcium chloride

(iii)    Oxygen

(iv)    Hydrogen chloride

(v)       Magnesium oxide

(vi)     Nitrogen

 

Answer

(i)   Sodium chloride – Ionic compound

(ii)  Calcium chloride – Ionic compound

(iii) Oxygen - Covalent compound

(iv) Hydrogen chloride - Covalent compound

(v)  Magnesium oxide - Ionic compound

(vi) Nitrogen - Covalent compound

Q11. An element ‘X’ has atomic no. 11 and ‘Y’ has atomic no. 8. What types of bonds they will form? Write the formula of the compound formed by reacting X and Y.

Answer

Element ‘X’ has atomic number 11 so it is sodium and element ‘Y’ has atomic number 8 so it is oxygen.

Electronic configuration of  Na= 2,8,1

Electronic configuration of  O = 2,6

Sodium atom loses one electron to form Na⁺ ion (2,8) to achieve stable configuration.

Oxygen atom gains 2 electrons to form O^2- ion (2,8) to achieve stable configuration.

These Na and O ions combine to form sodium oxide (Na₂O). It is an ionic compound.

 

Q12. Name the type of bonds present in H₂O molecule.

Answer

Water molecules has two types of bonds : covalent bond and hydrogen bond.

 Covalent bond is present between oxygen and hydrogen atoms and hydrogen bond present between two water molecules.