Chapter 7: CHEMICAL BONDING
Chapter 7: Chemical Bonding Class 10 Science and Technology (212) NIOS Textbook Solutions
Chapter 7. CHEMICAL BONDING
INTEXT QUESTIONS 7.1
1. State octet rule
Answer: The octet rule states that, atoms tend to gain, lose, or share electrons to achieve a stable outer shell containing 8 electrons (an octet), similar to the electronic configuration of noble gases.
2. Why noble gases are non-reactive?
Answer: Noble gases are non-reactive because they have a completely filled outermost electron shell (stable octet). Due to this stable electronic configuration, they do not easily gain, lose, or share electrons with other atoms.
3. In the table given below three elements and their atomic numbers are given. Which of them are stable and will not form compound?
|
Elements |
Atomic number |
Stable/Unstable |
|
A B C |
10 36 37 |
|
Answer:
|
Elements |
Atomic number |
Configuration |
Stable/Unstable |
|
A |
10 |
2.8 |
Stable |
|
B |
36 |
2.8.18.8 |
Stable |
|
C |
37 |
2.8.18.8.1 |
Unstable |
INTEXT QUESTIONS 7.2
1. Name the two types of ions present in NaCl.
Answer: Sodium ion Na⁺ (cation) and chloride ion Cl⁻ (anion) .
2. How many shells are present in Na+
ion?
Answer: Atomic number of sodium (Na) is 11 .
The electronic configuration of Na is 2. 8. 1 .
K L M
When it loses one electron to form Na⁺, the configuration becomes 2 . 8 .
K L
Therefore, Na⁺ ion has 2 shells (K and L shells).
3. What is the number of electrons present in Cl-
ion?
Answer: Atomic number chlorine 17.
The electronic configuration of Cl is 2. 8. 7 .
When it gains 1 electron to form Cl⁻, the total becomes = 17 + 1 = 18 electrons
So, Cl⁻ ion has 18 electrons.
4. Name the type of force of attraction present in ionic compounds.
Answer: The force of attraction present in ionic compounds is electrostatic force of attraction between positively charged ions (cations) and negatively charged ions (anions).
5. In sodium chloride lattice, how many 
ions surround each ion?
Answer: In a sodium chloride (NaCl) lattice, each Na⁺ ion is surrounded by 6 Cl⁻ ions.
So, 6 chloride ions (Cl⁻).
6. Show the formation of 
, 
and MgO.
Answer: kkkkkkkkkkk
7. Why NaCl is bad conductor of electricity in solid state?
Answer: NaCl is a bad conductor of electricity in solid state due to the absence of free Na⁺ and Cl⁻ ions. The ions are fixed in their positions and cannot move to carry electric current.
INTEXT QUESTIONS 7.3
1. How covalent bonds are formed?
Answer: A covalent bond is formed by sharing of equal number of electrons between two atoms.
2. Show the formation of 
, HCl, 
and 
.
Answer: : The atomic number of O is 8 .
Electronic configuration of O is 2. 6 .
HCl: The atomic number of H is 1 .
Electronic configuration of H is 1 .
The atomic number of Cl is 17 .
Electronic configuration of Cl is : 2. 8.7 .
: The atomic number of Cl is 17 .
Electronic configuration of Cl is : 2. 8.7 .
and : The atomic number of N is 7 .
Electronic configuration of N is : 2. 5 .
3. How many covalent bond(s) is/are present in following compounds:
(i) 
(ii) HCl (iii) (iv) 
Answer: (i) The number of covalent bond of H₂O is 2 .
Structure: H—O—H
(ii) The number of covalent bond of HCl is 1 .
Structure: H—Cl
(iii) The number of covalent bond of O₂ is 2 .
Structure: O = O
(iv) The number of covalent bond of N₂ is 3 .
Structure: N ≡ N
4. State loss or gain of elactrons (giving their number) in the following changes :
(i) N → N³⁻ (ii) 
(iii) 
(iv) 
Answer: (i) N → N³⁻ → Gains 3 electrons
(ii) Cl → Cl⁻ → Gains 1 electron
(iii) Cu → Cu²⁺ → Loses 2 electrons
(iv) Cr → Cr³⁺ → Loses 3 electrons
5. Why ethyl alcohol is bad conductor of electricity in its aqueous solutions?
Answer: 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?
Answer: Ionic compounds conduct electricity in aqueous solution because they dissociate into free-moving ions. These ions carry electric current through the solution.
2. Covalent compounds have low melting point than an ionic compound why?
Answer: Covalent compounds have low melting points because the force of attraction between their molecules is weak, so less heat energy is needed to separate them. Ionic compounds have strong electrostatic forces between ions.
3. Explain the formation of 
ion from Na atom.
Answer: Sodium (Na) has atomic number 11 and electronic configuration 2, 8, 1. To attain a stable octet, it loses one electron from its outermost shell and forms a Na⁺ ion with electronic configuration 2, 8.
Na → Na⁺ + e⁻
4. How would you explain the bonding in 
?
Answer: The atomic number of Mg is 12 .
Electronic configuration of Mg is 2. 8. 2
The atomic number of Cl is 17 .
Electronic configuration of Cl is 2. 8. 7 .
kkkkkkkkkkkkkkkk
In MgCl₂ (magnesium chloride), bonding is ionic (electrovalent).
Magnesium (Mg) has 2 valence electrons, and chlorine (Cl) needs 1 electron to complete its octet. So, magnesium loses 2 electrons, one to each of two chlorine atoms.
Mg → Mg²⁺ + 2e⁻
2Cl + 2e⁻ → 2Cl⁻
Then, Mg²⁺ and 2Cl⁻ ions are held together by a strong electrostatic force of attraction, forming 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.
Answer: The correct statements are: (ii) They are neutral in nature.
(iii) They have high melting points.
6. State three characteristic properties of ionic compounds.
Answer: Three characteristic properties of ionic compounds:
(i) They have high melting and boiling points due to strong electrostatic forces between ions.
(ii) They conduct electricity in molten or aqueous state, but not in solid state.
(iii) They are generally hard, brittle crystalline solids.
7. How does a covalent bond form?
Answer: A covalent bond is formed by the mutual sharing of one or more pairs of electrons between two atoms so that they attain a stable electronic configuration.
8. What is the number of colavent bonds present in the following molecules?
(i) 
(ii) (iii) (iv) 
Answer: (i) The number of colavent bonds of Cl₂ is 1 .
The structure: Cl—Cl
(ii) The number of colavent bonds of N₂ is 3 .
The structure : N ≡ N
(iii) The number of colavent bonds of O₂ is 2 .
The structure: O = O
(iv) The number of colavent bonds of H₂ is 1 .
The structure: H—H
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.
Answer: (i) Ionic compounds contain ions which are held together by weak electrostatic forces. → False
(ii) Ionic compounds have high melting and boiling points. → True
(iii) Covalent compounds are good conductors of electricity. → False
(iv) Solid sodium chloride is a good conductor of electricity. → 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
Answer:
|
Compound |
Type of Bond |
|
(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 they will form? Write the formula of the compound formed by reacting X and Y.
Answer: Atomic number of X is 11 .
Electronic configuration of X is 2.8.1
Atomic number of Y is 8 .
Electronic configuration of X is 2.6
Sodium loses 1 electrons and oxygen gains 2 electrons, so they form an ionic (electrovalent) bond.
Formula of the compound formed = X2Y .
12. Name the type of bonds present in
molecule.
Answer: The H₂O molecule contains covalent bonds between hydrogen and oxygen atoms.
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