Samacheer Class 9 Science - Chemical Bonding

Q: Number of valence electrons in carbon is

(a) 2 (b) 4 (c) 3 (d) 5 Answer: (b) 4

Q: Sodium (Atomic Number 11) tends to ______ electron(s) to attain noble gas configuration.

(a) gain one (b) gain two (c) lose one (d) lose two Answer: (c) lose one

Q: Element that forms an anion by gaining electrons is

(a) potassium (b) calcium (c) fluorine (d) iron Answer: (c) fluorine

Q: Bond formed between a metal and non-metal is usually

(a) ionic bond (b) covalent bond (c) coordinate bond Answer: (a) ionic bond

Q: ______ compounds generally have high melting and boiling points.

(a) Covalent (b) Coordinate (c) Ionic Answer: (c) Ionic

Q: Oxidising agents are called

(a) electron donors (b) electron acceptors Answer: (b) electron acceptors

Q: Elements with stable octet configuration are

(a) halogens (b) metals (c) noble gases (d) non-metals Answer: (c) noble gases

Your Progress — Chemical Bonding0% complete

1I. Choose the Correct Answer8 questions

Q.1Number of valence electrons in carbon is▾

✓ Answer

(a) 2
(b) 4
(c) 3
(d) 5

Answer:
(b) 4

Q.2Sodium (Atomic Number 11) tends to ______ electron(s) to attain noble gas configuration.▾

✓ Answer

(a) gain one
(b) gain two
(c) lose one
(d) lose two

Answer:
(c) lose one

Q.3Element that forms an anion by gaining electrons is▾

✓ Answer

(a) potassium
(b) calcium
(c) fluorine
(d) iron

Answer:
(c) fluorine

Q.4Bond formed between a metal and non-metal is usually▾

✓ Answer

(a) ionic bond
(b) covalent bond
(c) coordinate bond

Answer:
(a) ionic bond

Q.5______ compounds generally have high melting and boiling points.▾

✓ Answer

(a) Covalent
(b) Coordinate
(c) Ionic

Answer:
(c) Ionic

Q.6Covalent bond is formed by▾

✓ Answer

(a) transfer of electrons
(b) sharing of electrons
(c) sharing a pair of electrons

Answer:
(b) sharing of electrons

Q.7Oxidising agents are called▾

✓ Answer

(a) electron donors
(b) electron acceptors

Answer:
(b) electron acceptors

Q.8Elements with stable octet configuration are▾

✓ Answer

(a) halogens
(b) metals
(c) noble gases
(d) non-metals

Answer:
(c) noble gases

2II. Answer Briefly14 questions

Q.1How Do Atoms Attain Noble Gas Configuration?▾

✓ Answer

Answer:

Atoms attain stable noble gas electronic configuration by:

Transfer of valence electrons
Sharing of valence electrons

This results in stable octet configuration.

Q.2Why is NaCl Soluble in Water but Insoluble in Carbon Tetrachloride?▾

✓ Answer

Answer:

NaCl is an ionic compound.

Water is a polar solvent → dissolves ionic compounds.
Carbon tetrachloride ((CCl_4)) is non-polar → does not dissolve ionic compounds.

Hence NaCl dissolves in water but not in (CCl_4).

Q.3Explain Octet Rule with Example▾

✓ Answer

Answer:

Atoms tend to attain eight electrons in valence shell for stability.

This is called:

Octet Rule

Example

Sodium

Electronic configuration:

$$2,8,1$$

Sodium loses one electron:

Na \rightarrow Na^+ + e^-

It attains Neon configuration.

Chlorine

Electronic configuration:

$$2,8,7$$

Chlorine gains one electron:

Cl + e^- \rightarrow Cl^-

It attains Argon configuration.

Q.4Write Note on Different Types of Bonds▾

✓ Answer

Answer:

Main types of chemical bonds are:

Ionic bond
Covalent bond
Coordinate covalent bond

These bonds differ in:

mode of formation
strength
physical properties

Q.5Correct the Wrong Statements▾

✓ Answer

(a)

Incorrect:

“Ionic compounds dissolve in non-polar solvents.”

Correct:

Ionic compounds dissolve in polar solvents.

(b)

Incorrect:

“Covalent compounds conduct electricity in molten state.”

Correct:

Ionic compounds conduct electricity in molten or aqueous state.

Q.6Types of Bonds▾

✓ Answer

Bond Type	Formation
Ionic bond	Transfer of electrons
Covalent bond	Sharing of electrons
Coordinate bond	Sharing of electron pair by one atom

Q.7Formation of Carbon Dioxide Molecule▾

✓ Answer

Carbon Configuration

$$2,4$$

Oxygen Configuration

$$2,6$$

Carbon shares two pairs of electrons with each oxygen atom.

Structure:

$$O = C = O$$

Two double covalent bonds are formed.

Q.8Classify Compounds by Bond Type▾

✓ Answer

Compound	Bond Type
(CaCl_2)	Ionic
(H_2O)	Covalent
(CaO)	Ionic
CO	Coordinate + Covalent
KBr	Ionic
HCl	Covalent
(CCl_4)	Covalent
HF	Covalent
(CO_2)	Covalent
(Al_2Cl_6)	Coordinate covalent

Q.9Characteristic Property of Ionic Compounds▾

✓ Answer

Correct answer:

(b) hard and brittle

Q.10Identify Oxidation or Reduction▾

✓ Answer

(a)

Na \rightarrow Na^+ + e^-

Answer:

Oxidation

(loss of electron)

(b)

Fe^{3+} + 2e^- \rightarrow Fe^+

Answer:

Reduction

(gain of electrons)

Q.11Identify Compound Type▾

✓ Answer

Characteristic	Compound Type
Soluble in non-polar solvent	Covalent
Fast reactions	Ionic
Non-conductor	Covalent
Solid at room temperature	Ionic

Correction made:
“Coordinate covalent compound” in original answer was generalized incorrectly.

Q.12Dot Structure for Compound XY▾

✓ Answer

Given:

X → atomic number 20 → Calcium
Y → atomic number 8 → Oxygen

Compound formed:

$$CaO$$

Calcium transfers two electrons to oxygen.

Result:

Ca^{2+} \quad O^{2-}

Q.13Differences Between (MgCl_2) and (CH_4)▾

✓ Answer

(MgCl_2) (Ionic)	(CH_4) (Covalent)
Formed by electron transfer	Formed by electron sharing
Strong electrostatic attraction	Weak intermolecular force
Conducts electricity in molten state	Does not conduct electricity
High melting point	Low melting point

Q.14Why are Noble Gases Inert?▾

✓ Answer

Answer:

Noble gases possess completely filled valence shell.

Hence they:

neither gain electrons
nor lose electrons

Therefore they are chemically inert.

3III. Answer in Detail5 questions

Q.1Differences Between Ionic and Covalent Compounds▾

✓ Answer

Ionic Compounds	Covalent Compounds
Formed by electron transfer	Formed by electron sharing
Strong electrostatic force	Weak intermolecular force
Hard and brittle	Soft and waxy
High melting point	Low melting point
Conduct electricity in molten state	Non-conductors
Soluble in polar solvents	Soluble in non-polar solvents
Fast ionic reactions	Slow molecular reactions

Q.2Examples for Different Bond Types▾

✓ Answer

(a) Two Covalent Bonds

$$O_2$$

(b) One Ionic Bond

$$NaCl$$

(c) Two Covalent + One Coordinate Bond

$$CO$$

(d) Three Covalent Bonds

$$N_2$$

(e) Coordinate Bond

NH_3 \rightarrow BF_3

Q.3Correct Incorrect Statements▾

✓ Answer

(a)

Coordinate compounds generally do not contain ions.

Hence they are poor conductors.

(b)

Ionic bond is stronger than hydrogen bond.

(c)

Covalent bonds form by mutual sharing of electrons.

(d)

Correct statement.

Loss of electrons → oxidation
Gain of electrons → reduction

(e)

Electrons not involved in bonding are called:

Lone pair electrons

Q.4Properties of Coordinate Covalent Compounds▾

✓ Answer

(a) Physical State

Can exist as:

solids
liquids
gases

(b) Electrical Conductivity

Generally poor conductors.

(c) Melting Point

Intermediate between ionic and covalent compounds.

(d) Solubility

Soluble in non-polar solvents.

(e) Reactions

Undergo slow molecular reactions.

Q.5Oxidation Numbers▾

✓ Answer

# (a) Carbon in (CO_2)

$$x + 2(-2) = 0$$

$$x = +4$$

# (b) Manganese in (MnSO_4)

$$x + (+6) + 4(-2) = 0$$

$$x = +2$$

# (c) Nitrogen in (HNO_3)

$$(+1) + x + 3(-2) = 0$$

$$x = +5$$

# Important Summary

Ionic Bond

Electron transfer
Metal + Non-metal

Covalent Bond

Electron sharing
Non-metal + Non-metal

Coordinate Bond

Shared electron pair donated by one atom

Oxidation

Loss of electrons

Reduction

Gain of electrons

Noble Gases

Stable octet configuration
Chemically inert

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