Frank Brothers Solutions for ICSE Class 10 Chemistry Chapter 2 Chemical Bonding

Chapter 2. Chemical Bonding

Solution 1:
Answer: Chemical bond: A chemical bond may be defined as the linkage that stands for the force which actually holds the atoms together within the molecule. Chemical bonding: The phenomenon during which a chemical bond is formed is called chemical bonding.

📝 Teacher's Note: Use simple analogies like "atoms holding hands" or "magnets sticking together" to help students visualize chemical bonds. Draw simple diagrams showing atoms before and after bonding.

🎯 Exam Tip: Always define both "chemical bond" and "chemical bonding" separately as they are slightly different concepts that examiners often test.

Solution 2:
Answer: Atoms combine to attain the electronic configuration of nearest inert gases as the atoms of inert gases are very stable having 8 electrons or duplet (or 2 electrons in case of helium atom) in their outermost shell.

📝 Teacher's Note: Emphasize that atoms "want" to become stable like noble gases. Use the octet rule as a simple guideline, but mention helium needs only 2 electrons (duplet rule).

🎯 Exam Tip: Remember to mention both octet (8 electrons) and duplet (2 electrons for helium) configurations when explaining why atoms bond.

Solution 3:
Answer: Electrovalent compounds: The chemical compounds containing electrovalent bonds are called electrovalent or ionic compounds. For example: Sodium chloride (NaCl). Covalent compounds: The chemical compound, formed as a result of mutual sharing of electrons or electron pairs thereby establishing a covalent bond is called a covalent or molecular compound. For example: Hydrogen molecule (H₂)

📝 Teacher's Note: Use real-life examples like table salt (NaCl) for ionic and water (H₂O) for covalent compounds. Students relate better to familiar substances.

🎯 Exam Tip: Always provide examples when defining compound types - examiners award extra marks for relevant examples like NaCl and H₂.

Solution 4:
Answer: The conditions for the formation of an electrovalent bond are:

• Low ionization energy of electropositive atom
• High electron affinity of the electronegative atom
• Large electronegativity difference
• High lattice energy

Concept Insight:

• Lower is the ionization energy of atom, higher is its tendency to lose electron to form a cation and form ionic bond.
• Higher the value of electron affinity of an atom, greater will be its tendency to form anion and form ionic bond.
• If the electronegativity difference of two elements is higher, more easy will be the transfer of electrons and hence more chances of ionic bond formation.
• Lattice energy is the energy released when positive and negatively charged atoms called ions come closer to form a crystal because the attractive forces among the oppositely charged ions tend to decrease the energy of the system. Higher is the lattice energy, greater will be the ease of formation of the compound.

📝 Teacher's Note: Connect these conditions to real examples - metals (low ionization energy) + non-metals (high electron affinity) = ionic compounds. Use energy diagrams to show the energy changes.

🎯 Exam Tip: Learn all four conditions by heart and be able to explain WHY each condition favors ionic bond formation for full marks.

Solution 5:
Answer:

📝 Teacher's Note: Create a comparison chart on the board and ask students to predict properties based on bonding type. This helps them understand the cause-effect relationship between bonding and properties.

🎯 Exam Tip: Remember the key differences: ionic = high melting point, conduct when molten; covalent = low melting point, don't conduct electricity.

Solution 6:
Answer: Hydrogen chloride has a polar covalent bond because in hydrogen chloride the higher electronegativity of chlorine atom attracts the shared electron pair towards itself. As a result, the chlorine atom gets a partial negative charge while the hydrogen atom gets a partial positive charge. Hence such a covalent bond with charge separation is called polar covalent bond. While methane has a non polar covalent bond because in case of methane molecule the shared electron pairs are at equal distance from the carbon and hydrogen atoms, because neither the carbon atom nor the hydrogen atom has enough electronegativity difference between each other to attract the shared pairs of electrons towards itself. Hence no charge separation occurs in the covalent bond due to which it is called non polar covalent bond. Concept Insight: When a covalent bond is formed between the atoms of the same elements of equal electronegativity then the electron pairs are shared equally between the atoms and the bond so formed is called non polar covalent bond. On the other hand, if the covalent bond is formed between atoms of different elements, with difference in electro negativity, the electrons are not shared equally between the atoms. The more electronegative atom pulls the bonded pair of electrons towards itself and acquires negative charge while the other less electro negative atom acquires positive charge and the bond becomes polar covalent bond.

📝 Teacher's Note: Use the analogy of a "tug of war" between atoms - equal strength = non-polar, unequal strength = polar. Draw partial charges (δ+ and δ-) to show charge distribution.

🎯 Exam Tip: Always mention electronegativity difference and charge separation when explaining polar vs non-polar bonds - these are key marking points.

Solution 7:
Answer: In terms of electron transfer, oxidation is defined as the phenomenon in which an atom loses electron to form a positively charged cation while reduction is defined as the phenomenon in which an atom gains electron to form a negatively charged ion called anion. During formation of ionic bond one atom undergoes oxidation while another atom undergoes reduction.

📝 Teacher's Note: Teach the mnemonic "OIL RIG" - Oxidation Is Loss, Reduction Is Gain (of electrons). Connect this to ionic bond formation where one atom loses and another gains electrons.

🎯 Exam Tip: Remember: oxidation = electron loss = positive charge; reduction = electron gain = negative charge. Always mention both processes occur simultaneously in ionic bond formation.

Solution 8:
Answer: The diagrams show ionic bond formation through electron transfer:
(a) Magnesium loses 2 electrons to form Mg²⁺ ion, chlorine atoms gain electrons to form Cl⁻ ions, forming MgCl₂
(b) Calcium ion (Ca²⁺) combines with oxide ion (O²⁻) through electrostatic forces to form calcium oxide (CaO)
(c) Sodium ion (Na⁺) combines with chloride ion (Cl⁻) through electrostatic forces to form sodium chloride (NaCl)

📝 Teacher's Note: Use colored chalks or markers to show electron movement clearly. Emphasize that the + and - charges attract each other like magnets to form the ionic compound.

🎯 Exam Tip: When drawing ionic bond formation, always show: electron transfer arrows, correct charges on ions, and the final ionic compound formula.

Solution 9:
Answer: The diagrams show covalent bond formation through electron sharing:
(a) Orbit structure of N₂: Two nitrogen atoms share 3 pairs of electrons to form a triple covalent bond
(b) Two chlorine atoms share 1 pair of electrons to form a single covalent bond in Cl₂ molecule
(c) Two hydrogen atoms share 1 pair of electrons to form a single covalent bond in H₂ molecule

📝 Teacher's Note: Emphasize that electrons are SHARED, not transferred in covalent bonds. Use overlapping circles to show shared electron regions between atoms.

🎯 Exam Tip: For covalent bond diagrams, clearly show shared electron pairs between atoms and label them as "shared pair of electrons" for full marks.

Solution 10:
Answer:
1. Sodium chloride dissolves in water because it is an ionic compound and water is also a polar covalent compound. Water decreases the electrostatic forces of attraction among the sodium and chloride ions due to which these ions become free in water, hence sodium chloride dissolves. On the other hand, carbon tetra chloride has non polar covalent bond and water has polar covalent bond. Hence, water is unable to break the non polar covalent bond of carbon tetra chloride. So it is insoluble in water.
2. Helium does not form He₂ molecule as it has its outermost shell complete i.e. two electrons in its valence shell. Due to this complete valence shell helium atom is very stable hence does not participate in chemical bonding to form He₂ molecule.
3. Pure water does not conduct electricity because it has a polar covalent molecule hence does not have ions in it which can conduct electricity. On adding sodium chloride to pure water, sodium chloride breaks apart into sodium and chloride ions because water being polar decreases the strong forces of attraction among sodium and chloride ions. Now, pure water has ions present in it which can conduct electricity.
4. Cl₂ is a non polar molecule because the bond is between same atoms that is chlorine with zero electronegativity difference among them. So the shared electron pair is attracted equally by the two chlorine atoms hence there is no separation of charges in the bond formed so the chlorine molecule is non polar.
5. In case of HCl the bond is formed between two different atoms that is hydrogen and chlorine with enough electro negativity difference so that the shared electron pair is attracted towards more electronegative chlorine atom which acquires partial negative charge while the hydrogen atom acquires partial positive charge hence HCl is a polar molecule.
6. Metals have low ionization energy due to which they can lose their outermost electrons easily to form positive metallic ions hence metals are electropositive. For example Sodium metal always form Na⁺ ions, Potassium forms K⁺ ions etc.

📝 Teacher's Note: Connect solubility to the rule "like dissolves like" - polar dissolves polar, non-polar dissolves non-polar. Use demonstrations with salt, oil, and water to show this concept.

🎯 Exam Tip: For each explanation, mention the key factor: ionic/polar nature for solubility, complete valence shell for stability, presence of ions for conductivity, electronegativity difference for polarity.

Solution 11:
Answer:
1. (i) When the electro negativity difference between the two atoms is high then the bond formed will be purely ionic.
(ii) When the electro negativity difference between the two atoms is low then the bond formed will be polar covalent bond.
(iii) When the electro negativity difference between the two atoms is zero then the bond formed will be purely covalent.
2. Ionic compounds = NO, NH₄Cl, NH₄NO₃
Covalent compounds = N₂, NH₂, NO
Polar compounds = NCl₃ Concept Insight: Electro negativity difference between the bonded atoms determines the ease of transfer of electrons between the atoms. On the basis of extent of transfer of electrons between the two atoms the bond will be ionic, covalent or polar.

📝 Teacher's Note: Teach the electronegativity difference scale: >1.7 = ionic, 0.4-1.7 = polar covalent, <0.4 = pure covalent. This gives students a clear numerical guideline.

🎯 Exam Tip: Remember the classification based on electronegativity difference and be able to identify compound types based on the elements involved - metals with non-metals usually form ionic compounds.

Solution 12:

Electronic configuration of X shows that X is a metal.
Electronic configuration of Y shows that Y is a non metal.

(a) Since Y is a metal and thus electropositive:
\( Y \rightarrow Y^{2+} + 2e^- \)

while X is a non metal and thus electron negative:
\( X + 1e^- \rightarrow X^- \)

Hence two X atoms can combine with one Y atom to form \( YX_2 \) molecule and since the formation of \( YX_2 \) involves complete transfer of electrons between them so the bond between them is ionic.

(b)

\( [X]^+ + [Y]^- \rightarrow X^+ \leftrightarrow Y^- \)

Electrostatic force of attraction (ionic bond)

(c) The three main properties of this compound are:

• It is an ionic compound.
• It is soluble in water but insoluble in organic solvents.
• It is a good conductor of electricity in the molten state and in aqueous solution.

📝 Teacher's Note: Help students identify the key difference between ionic and covalent compounds by comparing their solubility and conductivity. Use everyday examples like salt dissolving in water versus oil not mixing with water.

🎯 Exam Tip: Always mention "complete transfer of electrons" for ionic bonds and list at least three properties with proper reasoning to score full marks.

Solution 13:

1. \( MgCl_2 \), \( CaCl_2 \).
2. Urea, Glucose.
3. \( CH_4 \), benzene.
4. \( SO_2 \), \( H_2S \)
5. \( H_2 \), \( N_2 \)

📝 Teacher's Note: Ask students to classify each compound type and explain why they belong to that category. This reinforces understanding of different bonding types.

🎯 Exam Tip: Memorize common examples of each compound type - it's frequently tested in identification questions.

Solution 14:

The necessary conditions for the formation of covalent molecule are:

1. Number of valence electrons: Both the participating atoms should have four or more valence electrons in their valence shell.

2. Equal electro negativities: The combining atoms should have equal electro negativities so that no transfer of electrons takes place.

3. Equal electron affinities: The combining atoms should also have equal electron affinities i.e. equal attraction for electrons.

4. Ionization energy: It should be high for both the atoms so that there is no chance of removal of electrons.

5. High nuclear charge and small inter nuclear distance: Both these conditions favor the formation of covalent bond because during the formation of a covalent bond the electron density gets concentrated between the nuclei of the combining atoms and this electronic charge is responsible for holding the two nuclei together.

The properties of covalent compounds are:

6. Nature: They are generally volatile liquids or gases. Some may be solids like urea, sugar etc.

7. Low melting and boiling points: Since the intermolecular forces of attraction are weak, very small amount of heat energy is required to overcome these forces hence their melting and boiling points are low.

8. Electrical conductivity: Since covalent compounds are made up of molecules and not ions, so they do not conduct electricity.

9. Solubility: These are insoluble in water but soluble in organic solvents.

10. Ionization in solution: These do not ionize when dissolved in water except some polar covalent compounds like HCl.

11. Molecular reactions: These participate in reactions as a molecule so the reactions are called molecular reactions. These are slow reactions.

📝 Teacher's Note: Emphasize the contrast with ionic compounds at each point. Use examples like sugar vs salt to show the difference in properties practically.

🎯 Exam Tip: Remember the phrase "like dissolves like" for solubility questions - polar substances dissolve in polar solvents, non-polar in non-polar.

Solution 15:

Coordinate bond: The bond formed between two atoms by a pair of electrons, provided entirely by one of the combining atoms, is called a coordinate bond or dative bond.

Conditions for the formation of coordinate bond:

1. One of the two atoms must have at least one lone pair of electrons.
2. Another atom should be short of at least a lone pair of electrons.

📝 Teacher's Note: Use the analogy of "lending and borrowing" - one atom lends its electron pair completely while the other borrows it. Draw simple diagrams showing lone pairs clearly.

🎯 Exam Tip: Always mention "provided entirely by one atom" to distinguish coordinate bonds from regular covalent bonds where electrons are shared equally.

Solution 16:

Lone pair: A pair of electrons which is not shared with any other atom is known as the lone pair of electrons.

For example in \( NH_3 \), Nitrogen has a lone pair of electrons which is not shared with any hydrogen atom.

Shared pair: A pair of electrons which is shared with other atoms to form a bond is known as shared pair of electrons.

For example in HCl the pair of electrons responsible for bond formation between H and Cl is called shared pair.

📝 Teacher's Note: Draw electron dot structures of \( NH_3 \) and HCl on the board to visually show lone pairs vs shared pairs. This makes the concept very clear for students.

🎯 Exam Tip: In electron dot diagrams, clearly mark lone pairs with dots or crosses to show you understand the difference between shared and unshared electrons.

Solution 17:

(a) Structure of hydronium ion: Hydronium ions (\( H_3O^+ \)) are formed when a hydrogen ion released from acid combines with water molecules.
Oxygen atom in water molecule attains an octet by forming two single covalent bonds with two hydrogen atoms but it still contains two lone pairs of electrons.
\( H_3O^+ \) is formed when the oxygen atom in water molecule donates a lone pair of electrons to a hydrogen ion thus establishing a coordinate bond between the oxygen atom and the hydrogen ion.

(b) Structure of Ammonium ion: Ammonium ion (\( NH_4^+ \)) is formed when a hydrogen ion or proton combines with ammonia molecule. Nitrogen atom in ammonia has a lone pair of electrons on it which it shares with the hydrogen ion which tends to acquire the configuration of helium atom. Thus, a co-ordinate bond results between nitrogen atom and hydrogen ion in ammonium ion.

📝 Teacher's Note: Emphasize that both ions form through coordinate bonding where the central atom donates electron pairs. Show students how to count electrons to verify the octet rule.

🎯 Exam Tip: Always draw the complete structure showing lone pairs and indicate the coordinate bond with an arrow pointing from donor to acceptor atom.

Solution 18:

1. The forces of attraction between the molecules of covalent compounds are weak because the molecules are neutral. So, they are generally gases or liquids or soft solids.

2. Covalent compounds have low melting and boiling point because the intermolecular forces of attraction among the molecules of covalent compounds are weak. Hence very small amount of heat energy is required to overcome the attraction between the molecules.

3. On the basis of principle like dissolves like we can interpret the insolubility of non polar covalent compounds. Since water is a polar covalent compound that is it has positively and negatively charged ends but the non-polar covalent compounds do not have any kind of charge separation. So water molecules are unable to interact with the molecules of non polar compound and break apart the intermolecular forces of attraction among non-polar molecules making them soluble in water.

4. Polar covalent compounds are good conductors of electricity because when these are dissolved in water, they ionize and act as electrolyte to produce ions which are responsible for conduction of electricity.

For example polar covalent compound HCl in water behaves as:
\( HCl + H_2O \rightarrow H_3O^+ + Cl^- \)

These hydronium and chloride ions produced on dissolution of HCl in water are responsible for conduction of electricity.

📝 Teacher's Note: Use oil and water separation as a practical demonstration of "like dissolves like" principle. Students can easily relate to this everyday observation.

🎯 Exam Tip: For polarity questions, always mention charge separation and use the "like dissolves like" principle to explain solubility patterns.

📝 Teacher's Note: Highlight how the same element (phosphorous) can form different compounds with varying properties. This shows the importance of valence electrons in bonding.

🎯 Exam Tip: In comparison tables, always check that your bonding type matches with the physical properties you've listed.

Solution 2004-1:

(a) For element X:
\( X \rightarrow X^{2+} + 2e^- \)

For element Y:
\( Y + 3e^- \rightarrow Y^{3-} \)

(b) Since Y is a diatomic gas hence it combines with X as:
\( 3X + Y_2 \rightarrow X_3Y_2 \)

📝 Teacher's Note: Emphasize the importance of balancing charges when writing ionic formulas. Show students how to cross-multiply the charges to get the correct subscripts.

🎯 Exam Tip: Always check that the total positive and negative charges balance out in your ionic compound formula.

Solution 2005-1:

(a) (i) C
(ii) c
(iii) d

(b)(i) Acids dissolve in water to form positively charged ions which are generally hydrogen ions (\( H^+ \)).
Structure of Hydrogen ion: As hydrogen element has only one electron in its valence shell which is lost during formation of hydrogen ions so its structure is:

[Diagram showing \( H^+ \) structure]

(ii) Carbon tetrachloride is a non polar covalent compound. It do not ionize in water. Since water is a polar covalent compound that is it has positively and negatively charged ends but the non-polar covalent compounds do not have any kind of charge separation. So water molecules are unable to interact with the molecules of non polar compound and break apart the intermolecular forces of attraction among non-polar molecules, this is the reason for which \( CCl_4 \) is insoluble in water.

(iii) Solid

(iv) No, because Q and S react together to form ionic compound in which one element lose electron while the other element accepts the electron. Now only metals can lose electron and non metal can accept electron that's why both Q and S cannot be metals.

📝 Teacher's Note: Stress that hydrogen ion is just a proton with no electrons - this unique structure explains many acid properties. Use the analogy of a "naked proton" to make it memorable.

🎯 Exam Tip: For polarity questions, always explain both the polar and non-polar nature of the substances involved to show complete understanding.

Solution 2006-1:
(i) A pair of electrons which is not shared with any other atom is known as lone pair of electrons.

(ii) [Chemical diagram showing formation of hydronium ion from water and hydrogen ion]

(iii) Ammonia

📝 Teacher's Note: Use visual models or electron dot diagrams to show lone pairs clearly. Students often confuse lone pairs with bonding pairs, so emphasize that lone pairs belong to only one atom.

🎯 Exam Tip: Always identify lone pairs by counting total valence electrons minus bonding electrons, then divide by 2. Draw clear dots or lines to show lone pairs in diagrams.

Solution 2006-2:
1. (b)
2. (a)

📝 Teacher's Note: Without the original questions, focus on helping students understand the context behind these answers. Review the concepts that led to these specific choices.

🎯 Exam Tip: When answering multiple choice questions, eliminate obviously wrong options first, then choose from remaining viable options based on core concepts.

Solution 2007-1:
(a) The charged particles which attract one another to form electrovalent compounds are called ions. Those having positive charge are called cations and those having negative charge are called anions.

(b) In the formation of covalent compound the electrons are shared between the combining atoms.

(c) Two electrons of a nitrogen atom are not involved in the formation of a nitrogen molecule since \( N_2 \) contains triple bond formed by sharing of three electrons from each nitrogen atom.

[Chemical diagram showing nitrogen atoms forming nitrogen molecule with shared electron pairs]

(d) In the formation of magnesium chloride magnesium is oxidized as it is metal and chlorine is reduced as it is non metal.
Mg → \( Mg^{2+} \) + 2e⁻
Cl + 1e⁻ → Cl⁻

📝 Teacher's Note: Use the analogy of "sharing toys" for covalent bonds and "giving/taking toys" for ionic bonds. This helps students visualize electron behavior in different bond types.

🎯 Exam Tip: For ionic compounds, always mention electron transfer and charge formation. For covalent compounds, emphasize electron sharing. Use correct chemical notation for ions.

Solution 2008-1:
ionises when dissolved in water

📝 Teacher's Note: Demonstrate ionization using simple salt solutions and conductivity tests. Students can observe how substances that don't conduct electricity as solids become conductive when dissolved.

🎯 Exam Tip: Remember that ionization in water produces mobile ions that can conduct electricity. This is a key property that distinguishes ionic from covalent compounds.

Solution 2008-2:
1. Covalent bond.
2. Co-ordinate bond

📝 Teacher's Note: Show the difference between covalent bonds (equal sharing) and coordinate bonds (one atom provides both electrons). Use examples like \( NH_3 \) and \( BF_3 \) forming \( NH_3BF_3 \).

🎯 Exam Tip: For coordinate bonds, identify which atom has the lone pair and which has the empty orbital. Always show the arrow pointing from donor to acceptor atom.

Solution 2009-1:
1. solid
2. low

📝 Teacher's Note: Connect physical states to molecular forces. Solids have strong intermolecular forces, while low values typically refer to properties like volatility or solubility depending on context.

🎯 Exam Tip: When describing states of matter, consider temperature, pressure, and intermolecular forces. "Low" properties often relate to weak intermolecular interactions.