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Selina Concise Chemistry Class 10 ICSE Solutions Chemical Bonding

November 10, 2023May 13, 2022 by Veerendra

Selina Concise Chemistry Class 10 ICSE Solutions Chemical Bonding

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Selina ICSE Solutions for Class 10 Chemistry Chapter 2 Chemical Bonding

Exercise Intext 1

Solution 1.

Atoms lose, gain or share electrons to attain noble gas configuration.

Solution 2.

(a) A chemical bond may be defined as the force of attraction between any two atoms, in a molecule, to maintain stability.
(b) The chemical bond formed between two atoms by transfer of one or more electrons from the atom of a metallic electropositive element to an atom of a non-metallic electronegative element.
(c) The chemical bond formed due to mutual sharing of electrons between the given pairs of atoms of non-metallic elements.

Solution 3.

Conditions for formation of Ionic bond are:

The atom which changes into cation should possess 1, 2 or 3 valency electrons. The other atom which changes into anion should possess 5, 6 or 7 electrons in the valence shell.
A high difference of electronegativity of the two atoms is necessary for the formation of an Ionic bond.
There must be an overall decrease in energy i.e., energy must be released.
For this an atom should have low value of Ionisation potential and the other atom should have high value of electron affinity.
Higher the lattice energy, greater will be the case of forming an ionic compound.

Solution 4.

It will form a cation: M³⁺M₂(SO₄)₃M(NO₃)₃M₃(PO₄)₃M₂(CO₃)₃M(OH)₃

Solution 5.

Atoms combine with other atoms to attain stable octet or noble gas configuration.

Solution 6.

Ionic compounds are generally formed between metals and non-metals as metals always lose electrons to form cations while non-metals gain electrons forming anions to complete their octet. These oppositely charged ions are held together by electrostatic force of attraction and hence results in an ionic compound.

Solution 7.

Selina Concise Chemistry Class 10 ICSE Solutions Chemical Bonding img 1

Solution 8.

(a) X has 7 electrons in its outermost shell and Y has only one electron in its outermost shell so Y loses its one electron and X gains that electron to form an ionic bond.
(b) The formula of the compound would be XY.

Solution 9.

Selina Concise Chemistry Class 10 ICSE Solutions Chemical Bonding img 2

Solution 10.

(a) Sodium atom and sodium ion

Sodium atom has one electron in M shell while sodium ion has 8 electrons in L shell.
Sodium atom is neutral while sodium ion is positively charged.
Sodium atom is highly reactive while its ion is inert.
Sodium atom is poisonous while sodium ion is non-poisonous.

(b) Chlorine atom and chlorine ion

Chlorine atom has 7 electrons in its M shell while Chloride ion has 8 electrons in the same shell.
Chlorine atom is neutral while chloride ion is negatively charged.
Chlorine atom is highly reactive while its ion is inert.
Chlorine gas is poisonous while chloride ion is non-poisonous.

Solution 11.

Fluoride ion is negatively charged while neon atom is neutral.

Solution 12.

(a) Transfer of electron(s) is involved in the formation of an electrovalent bond. The electropositive atom undergoes oxidation, while the electronegative atom undergoes reduction. This is known as a redox process.

Oxidation: In the electronic concept, oxidation is a process in which an atom or ion loses electron(s).
Zn → Zn²⁺+ 2e^–

Reduction: In the electronic concept, the reduction is a process in which an atom or ion accepts electron(s).
Cu²⁺ + 2e^–→ Cu

(b)

Zn → Zn²⁺+ 2e^– (Oxidation)
Pb²⁺+ 2e^– → Pb (Reduction)
Zn → Zn²⁺+ 2e^– (Oxidation)
Cu²⁺+ 2e^–→ Cu (Reduction)
Cl₂ + 2e^–→ 2Cl^– (Reduction)
2Br^–→ Br₂ + 2e^–(Oxidation)
Sn²⁺→ Sn⁴⁺ + 2e^– (Oxidation)
2Hg²⁺+ 2e^–→ Hg₂(Reduction)
Cu⁺→ Cu²⁺+ e^–(Oxidation)
Cu⁺+ e^–→ Cu (Reduction)

(c)

2K + Cl₂→2KCl

Oxidation: In the electronic concept, oxidation is a process in which an atom or ion loses electron(s).
K → K⁺+ e^–
Reduction: In the electronic concept, the reduction is a process in which an atom or ion accepts electron(s).
Cl₂ + 2e^–→ 2Cl^–
Oxidising agent
An oxidising agent oxidises other substances either by accepting electrons or by providing oxygen or an electronegative ion, or by removing hydrogen or an electropositive ion.
Cl₂ + 2e^–→ 2Cl^–
Reducing agent
A reducing agent reduces other substances either by providing electrons or by providing hydrogen or an electropositive ion, or by removing oxygen or an electronegative ion.
K → K⁺+ e^–

Exercise Intext 2

Solution 1.

(i) Both atoms should have four or more electrons in their outermost shells, i.e., non-metals.
(ii) Both the atoms should have high electronegativity.
(iii) Both the atoms should have high electron affinity and high ionisation potential.
(iv) Electronegativity difference between the two atoms should be zero or negligible.
(v) The approach of the atoms towards one another should be accompanied by decrease of energy.

Solution 2.

(a) A is a non-metal; B is a metal while C is a chemically inert element.
(b) BA

Solution 3.

(a) (i) E (ii) B
(b) C₂D
(c) A and C are metals while B, D and E are non -metals.

Solution 3(2017).

Selina Concise Chemistry Class 10 ICSE Solutions Chemical Bonding img 4

Solution 4.

(a) Ionic compounds are formed as a result of transfer of one or more electrons from the atom of a metallic electropositive element to an atom of a non-metallic electronegative element.
A polar covalent compound is the one in which there is an unequal distribution of electrons between the two atoms.

(b) Ionic compounds, made up of ions, are generally crystalline solids with high melting and boiling points.
They are soluble in water and good conductors of electricity in aqueous solution and molten state.
Covalent compounds, made up of molecules, can exist as soft solids or liquids or gases with low melting and boiling points. They are generally insoluble in water and poor conductors of electricity.

(c) Polar covalent compounds are formed between 2 non-metal atoms that have different electronegativities and therefore have unequal sharing of the bonded electron pair. Non-polar compounds are formed when two identical non-metals equally share electrons between them.

Solution 5.

(a) X⁺(b) X will be a strong reducing agent as it will have the tendency to donate its valence electron.

Solution 6.

Covalent compounds are said to be polar when shared pair of electrons are unequally distributed between the two atoms. For example in HCl, the high electronegativity of the chlorine atom attracts the shared electron pair towards itself. As a result, it develops a slight negative charge and hydrogen atom develops a slight positive charge. Hence, a polar covalent bond is formed.

Solution 7.

During the formation of a non-polar covalent bond between two similar atoms or dissimilar atoms, the atoms involved in sharing share the electrons equally. The molecule of methane has four carbon-hydrogen single covalent bonds. It is a non-polar covalent compound as the electrons are shared by the carbon and hydrogen atoms equally and hence the shared pair lies between the atoms at an equal distance from both carbon and hydrogen atom.

Solution 7.

Selina Concise Chemistry Class 10 ICSE Solutions Chemical Bonding img 6

b. Methane is a covalent compound and is non-polar in nature. This is because the shared pair of electrons is equally distributed between the two atoms. So, no charge separation takes place and the molecule is symmetrical and electrically neutral.

Solution 8.

(a) Properties of Ionic Compounds:

Ionic compounds usually exist in the form of crystalline solids.
Ionic compounds have high melting and boiling points.
Ionic compounds are generally soluble in water but insoluble in organic solvents.
They are good conductors of electricity in the fused or in aqueous solution state.

(b) Properties of Covalent Compounds:

The covalent compounds exist as gases or liquids or soft solids.
The melting and boiling points of covalent compounds are generally low.
Covalent compounds are insoluble in water but dissolve in organic solvents.
They are non-conductors of electricity in solid, molten or aqueous state.

Solution 9.

(a)

A reaction in which oxidation and reduction occur simultaneously is called an oxidation-reduction, or simply, a redox reaction.
Redox reactions involve the transfer of electrons between two chemical species.
The reaction in which electron is gained is called a reduction reaction and the reaction in which electron is lost is called oxidation reaction.
The compound that loses an electron is said to be oxidized, the one that gains an electron is said to be reduced.

Selina Concise Chemistry Class 10 ICSE Solutions Chemical Bonding img 7

(c)
(i) Potassium undergoes oxidation as it loses an electron and forms a cation.
(ii) Chlorine undergoes reduction as it gains an electron and forms chloride anion.
(iii) Potassium acts a reducing agent and gets oxidised.
(iv) Chlorine acts an oxidizing agent and gets reduced.

Solution 9.

Selina Concise Chemistry Class 10 ICSE Solutions Chemical Bonding img 8

Solution 10.

(a) Electrovalent compounds in the solid state do not conduct electricity because movement of ions in the solid state is not possible due to their rigid structure. But these compounds conduct electricity in the molten state. This is possible in the molten state since the electrostatic forces of attraction between the oppositely charged ions become weak. Thus, the ions move freely and conduct electricity.

(b) The atoms of covalent compounds are bound tightly to each other in stable molecules, but the molecules are generally not very strongly attracted to other molecules in the compound. On the other hand, the atoms (ions) in electrovalent compounds show strong attractions to other ions in their vicinity. This generally leads to low melting points for covalent solids, and high melting points for electrovalent solids.

(c) Electrovalent compounds dissolve in polar solvents like water because the forces of attraction between positive and negative charges become weak in water. But since covalent compound are made up of molecules, they do not ionize in water and hence do not dissolve in water.

(d) Since it takes a lot of energy to break the positive and negative charges apart from each other, the ionic compounds are so hard. But on applying stress, Ions of the same charge are brought side-by-side and so the opposite ions repel each other and crystal breaks into pieces.

(e) Since polar covalent compounds are made up of charged particles, they conduct electricity in aqueous solution.

Solution 10.

Dipole molecule is a molecule that has both, slight positive and slight negative charge.
For example, in HCl hydrogen has a slight positive charge and chlorine has a slight negative charge. The dipole moment of HCl molecule is 1.03 D and may be represented as:

Solution 11.

i. Y = 9
ii. Z = 12

b. Ionic bond with molecular formula ZY₂.

Solution 12.

MgCl₂ – Electrovalent compound	CCl₄ – Covalent compound
They are hard crystalline solids consisting of ions.	These are gases or liquids or soft solids.
They have high melting and boiling points.	They have low melting and boiling points.
They conduct electricity in the fused or aqueous state.	They do not conduct electricity in the solid, molten or aqueous state.
These are soluble in inorganic solvents but insoluble in organic solvents.	These are insoluble in water but dissolve in organic solvents.

Solution 13.

Potassium chloride is an electrovalent compound and conducts electricity in the molten or aqueous state because the electrostatic forces of attraction weaken in the fused state or in aqueous solution.

Polar covalent compounds like hydrogen chloride ionise in their solutions and can act as an electrolyte. So, both can conduct electricity in their aqueous solutions.

Solution 14.

a. HCland NH₃

b. HCl + H₂O → H₃O⁺ + Cl^–NH₃ + H₂O →NH₄⁺ + OH^–

Solution 15.

Formula of compound when combined with sulphur – MSFormula of compound when combined with chlorine –MCl₂

Solution 16.

Selina Concise Chemistry Class 10 ICSE Solutions Chemical Bonding img 10
(c) If the compound formed between A and B is melted and an electric current is passed through the molten compound, then element A will be obtained at the cathode and B at the anode of the electrolytic cell.

Exercise 1

Solution 1.

The bond formed between two atoms by sharing a pair of electrons, provided entirely by one of the combining atoms but shared by both is called a coordinate bond. It is represented by an arrow starting from the donor atoms and ending in the acceptor atom.

Conditions:

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

The two lone pair of electrons in the oxygen atom of water is used to form coordinate bond with the hydrogen ion which is short of an electron resulting in the formation of the hydronium ion.

H₂O + H⁺ H₃O⁺ Over here the hydrogen ion accepts one lone pair of electrons of the oxygen atom of water molecule leading to the formation of a coordinate covalent bond.

Solution 2.

A pair of electrons which is not shared with any other atom is known as a lone pair of electrons. It is provided to the other atom for the formation of a coordinate bond.

A pair of electrons which is shared between two atoms resulting in the formation of a covalent bond is called a shared pair.

Solution 3.

a. Polar covalent bond
b. Ionic bond
c. O and H are bonded with a single covalentbond and oxygen possesses a single negative charge in the hydroxyl ion.
d. Covalent bond
e. Coordinate bond
f. Electrovalentbond, dative bond (or coordinate bond) and covalent bond

Solution 4.

Solution 5.

Solution 6.

	Sodium	Phosphorus	Carbon
Formula of chloride	NaCl	PCl₅	CCl₄
Nature of bonding	Ionic	Covalent	Covalent
Physical state of chloride	Solid	Solid	Liquid

Solution 7.

a.
CaO- 1 calcium atom + 1 oxygen atom
Cl₂ – 2 chlorine atoms
H₂O – 2 hydrogen atoms + 1 oxygen atom
CCl₄ – 1 carbon atom + 4 chlorine atoms

Ca – will donate two electrons
O – will accept two electrons
Cl – will accept one electron, so two Cl atoms will share an electron pair.
C – will accept four electrons by sharing electrons pairs with hydrogen forming covalent bonds.
H – will donate one electron by sharing an electron pair with carbon.

Solution 8.

(a) Unequal, polar
(b) Middle, equally
(c) Electrovalent, electrostatic

Solution 9.

Y is getting reduced.
Y is positive and it will migrate towards negative electrode that is cathode.

Solution 10.

Selina Concise Chemistry Class 10 ICSE Solutions Chemical Bonding img 12

Solution 1 (2004).

Solution 1 (2005).

(a) (i) C (ii) C (iii) D
(b) (i)reduced (ii) negative
(c) (i) H₃O⁺ions
Selina Concise Chemistry Class 10 ICSE Solutions Chemical Bonding img 14
(ii) Like dissolves like. Since carbon tetrachloride is non-polar and water is polar compound, carbon tetrachloride does not dissolve in water.
(iii) Solid
(iv) No as ionic bonds can only be made by transfer of electrons from a metal to non metal.

Solution 1 (2006).

(a) (i) B (ii) A
(b) (i) Reduction
(ii) Oxidation
(iii) Reduction

Solution 1 (2007).

(i) Ions
(ii) Electrons are shared between the atoms of two or more elements
(iii) Two
(iv) Magnesium is oxidized and chlorine is reduced

Solution 1 (2008).
(a)
(i) D
(b)
(i) Covalent bond
(ii) Coordinate bond.

Solution 1 (2009).
Selina Concise Chemistry Class 10 ICSE Solutions Chemical Bonding img 15

Solution 1 (2010).

a. Oxidation

b.
i. ionic bond
ii. covalent and oordinate bond
iii. covalent bond

Solution 1 (2011).

c. HCl is a covalent compound formed by sharing one electron between chlorine and hydrogen. Because chlorine is more electronegative than hydrogen, the shared pair of electrons shifts towards the chlorine atom. So, a partial negative charge (δ^–) develops on chlorine and a partial positive charge (δ⁺) develops on hydrogen. Hence, the covalent bond is polar in nature.

Solution 1 (2012).

Selina Concise Chemistry Class 10 ICSE Solutions Chemical Bonding img 17

Solution 1 (2013).

a. Dative or coordinate bond
b. B Ammonium chloride
c. C Are insoluble in water
d.

Carbon tetrachloride	Sodium chloride
It is insoluble in water but dissolves in organic solvents.	It is soluble in water but insoluble in organic solvents.
It is a non-conductor of electricity due to the absence of ions.	It does not conduct electricity in the solid state but conducts electricity in the fused or aqueous state.

Solution 1 (2014).

a. B
b. D
c. Ionisation
d. Their constituent particles are molecules. These exist as gases or liquids or soft solids because they have weak forces of attraction between their molecules.

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ICSE Solutions for Class 10 Chemistry – Chemical Bonding

November 10, 2023May 12, 2022 by Raju

ICSE Solutions for Class 10 Chemistry – Chemical Bonding

ICSE Solutions Selina ICSE Solutions

APlusTopper.com provides ICSE Solutions for Class 10 Chemistry Chapter 2 Chemical Bonding for ICSE Board Examinations. We provide step by step Solutions for ICSE Chemistry Class 10 Solutions Pdf. You can download the Class 10 Chemistry ICSE Textbook Solutions with Free PDF download option.

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Short Questions

Question 1: The combination of atoms to form molecules is based on octel rule. Give two limiations of this rule.
Answer: (i) It cannot explain the formation of molecules like BeF₂, BF₃ in which the central atom has less than 8 electrons in its valence shell.
(ii) It cannot explain the formation of molecules such as PF₅, SF₆ etc., in which central atom has more than eight electrons in its valence shell.

Question 2: Write the general characteristics of electrovalent compounds.
Answer: The general characteristics of electrovalent compounds are:
(i) Electrovalent compounds are mostly crystalline in nature.
(ii) Electrovalent compounds form hard crystals. These crystals are usually brittle.
(iii) Electrovalent compounds have high density with high melting and boiling points.
(iv) Electrovalent compounds are soluble in polar solvents.
(v) Electrovalent compounds exhibit isomorphism.
(vi) They react very fast.

Question 3: On what factors the formation of an electrovalent compound depends ?
Answer: The formation of an ionic compound depends on the following factors:
(i) Low ionisation energy: Lesser is the ionisation energy of an atom, greater will be its tendency to form cation by losing the valence electron. Metals with lower ionisation energy values have a greater tendency to form ionic bonds.
(ii) High electron affinity: Higher the value of electron affinity, greater will be the tendency of the atom to gain electron and form an anion. Elements with high electron affinity values form ionic compounds.
(iii) High lattice energy: The higher is the value of lattice energy, greater will be the electrostatic force of attraction between the oppositely charged ions and hence ionic compounds are formed with greater ease by release of energy.

Question 4: What are the salient features of electrovalency ?
Answer: Some salient features of electrovalency are mentioned below :
(i) An electrovalent bond is formed by loss or gain or transfer of electrons.
(ii) Ions are formed during the formation of an electrovalent bond.
Positive ions —> Cations (Na⁺, K⁺, Ca²⁺, etc.)
Negative ions —> Anions (Cl^–, O^2-, N^3-, etc.)
(iii) An electrostatic force of attraction exist between the oppositely charged ions.
(iv) There is one fixed direction in space among the ions.

Question 5: Write important general characteristics of covalent compounds.
Answer: The important general characteristics of covalent compounds are as follows:
(i) Usually covalent compounds exist in gaseous, liquid or amorphous state.
(ii) Covalent compounds have low melting or boiling points.
(iii) Except for graphite, covalent compounds are bad conductors of electricity.
(iv) Covalent compounds are soluble in non polar solvents (usually organic solvents). Polar cgvalent compounds are however soluble in polar solvents.
(v) Covalent compounds contain molecules and they undergo reactions slowly.
(vi) Many covalent compounds exhibit various types of isomerism.

Question 6: (i) Name the charged particles which attract one another to form electrovalent compounds.
(ii) In the formation of electrovalent compounds, electrons are transferred from one element to another. How are electrons involved in the formation of a covalent compound ?
(iii) The electronic configuration of nitrogen is 2, 5. How many electrons in the outer shell of a nitrogen atom are not involved in the formation of a nitrogen molecule ?
(iv) In the formation of magnesium chloride (by direct combination between magnesium and chlorine), name the substance that is oxidised and the substance that is reduced.
Answer: (i) Cation and anion
(ii) There is a mutual sharing of electrons
(iii) 2
(iv) Magnesium is oxidised and chlorine is reduced.

Question 7: In the formation of compound XY₂, atorix X gives one electron to each Y atom. What is the nature of bond to XY₂ ? Give four properties of XY₂.
Answer: The bond in XY₂ is ionic.
Properties:
(i) It is hard and brittle.
(ii) It is soluble in water.
(iii) It has high melting and boiling point.
(iv) It does not conduct electric current in the solid state but conducts electric current in the molten or dissolved state.

Question 8: There are three elements E, F, G with atomic numbers 19, 8 and 17 respectively.
(i) Classify the elements as metals and non-metals.
(ii) Give the molecular formula of the compound formed between E and G and state the type of chemical bond in this compound.
Answer:
ICSE Solutions for Class 10 Chemistry - Chemical Bonding 1

Question 9: (i) Give one property of hydrogen chloride which agrees with it being a covalent compound.
(ii) Give one property of magnesium chloride which agrees with it being an ionic compound.
(iii) Name one compound which is covalent, but on dissolving in water conducts electricity ?
(iv) Which property of the above compound agrees with the being of a covalent compound ?
Answer: (i) Hydrogen chloride is a gas at room temperature and in dry state it is a bad conductor of electricity.
(ii) Magnesium chloride in the molten state or in aqueous solution is a good conductor of electricity and therefore is an ionic compound.
(iii) Hydrogen chloride.
(iv) Hydrogen chloride is a gas. In dry state, it is bad conductor of electricity. Hence, it is a covalent compound.

Question 10: A compound has the formula H₂Y (Y = Non-metal). State the following :
(i) the outer electronic configuration of Y.
(ii) the valency of Y.
(iii) the bonding present in H₂Y.
(iv) the formula of the compound formed between calcium \(_{ 20 }^{ 40 }{ Ca }\) and Y.
Answer: (i) Y has six electrons in its valence shell.
(ii) 2
(iii) Covalent
(iv)
ICSE Solutions for Class 10 Chemistry - Chemical Bonding 2

Question 11: Elements X, Y and Z have atomic number 6, 9 and 12 respectively. Which are :
(i) forms an anion (ii) forms a cation ?
(iii) has four electrons in its valence shell ?

Element	Atomic No.	Electronic configuration
X	6	2,4
Y	9	2,7
Z	12	2,8,2

Answer: (i) Y will form an anion (ii) Z forms a cation
(iii) X has four electrons in its valence shell.

Question 12: (i) Name two compounds that are covalent when taken pure but produce ions when dissolved in water.
(ii) For each compound, give the formulae of the ions formed in aqueous solutions.
(iii) Give the structure of hydroxyl ion.
Answer: (1) Hydrogen chloride and hydrogen bromide.
ICSE Solutions for Class 10 Chemistry - Chemical Bonding 3

Question 13: How is a co-ordinate bond formed?
Answer: The formation of co-ordinate bond between two atoms to occur in the following two steps:
E.g. two atoms are A and B—in the first step the donor atom A transfers one electron of its lone pair to the acceptor atom B. This result in that atom A develops unit positive charge and atom B develops a unit negative charge. This charge is known as formal charge. This is similar to the formation of ionic bond.
In the second step the two electrons, one each with A and B- are shared by both the ions. This is similar to the formation of covalent bond.
ICSE Solutions for Class 10 Chemistry - Chemical Bonding 4
Thus, a co-ordinate bond is equivalent to a combination of an electrovalent bond and a covalent bond. Hence it is also called a semipolar bond or dotive bond.

Question 14: What are the characteristics of co-ordinate compounds?
Answer: The general characteristics of co-ordinate compounds are as follows:
(i) Co-ordinate compounds are identical to normal covalent compounds.
(ii) It is rigid and has directional properties.
(iii) These compounds are soluble in non-polar solvents and insoluble in polar solvent.
(iv) These compounds behave as non-conductors of electricity.
(v) The melting and boiling points are higher than covalent compounds and lower than ionic compounds.
(vi) These are stable compounds.

Question 15: Which conditions are necessary for the formation of co-ordinate bond?
Answer: For the formation of a co-ordinate bond the atom acting as a donor must have one unused pair of electrons which may be donated by it to the acceptor atom. The acceptor atom must have an empty orbital to accept the lone pair of electrons.

Question 16: Explain the formation of H₃O⁺ and NH₄⁺ ion.
Answer: Formation of Hydronium ion, H₃O⁺ : This ion formed by the combination of H₂O molecule and H⁺ ion. The water molecule has two O—H covalent bonds and central oxygen atom has two lone pairs of electrons. H⁺ ion has one vacant ls-orbital. During the formation of H₃O⁺, one pair of lone pair from O-atom is donated to the vacant ls-orbital of H⁺ ion and O — H co-ordinate bond is formed. Thus H₃O⁺ ion contains two O—H covalent bonds and one O— H co-ordinate bond. After the formation O→ H⁺ co-ordinate bond becomes identical to the two O—H covalent bonds.
Hence in H₃O⁺ ion all the three bonds are identical.
ICSE Solutions for Class 10 Chemistry - Chemical Bonding 5
Formation of NH₄⁺, Ammonium ion : This ion formed by the combination of NH₃ molecule and H+ ion. In NH₃ molecule each of three H-atoms is linked to N-atom by a covalent bond. Thus in this molecule N-atom is left with a lone pair of electrons after completing its. octet by sharing three of its valence shell electrons with three H-atoms. The electrons of lone pair on N-atom are donated to H⁺ ion and thus a N/EH co-ordinate bond is established in NH₄⁺ ion.
ICSE Solutions for Class 10 Chemistry - Chemical Bonding 6

Question 17: What is lone pair effect ? In what kind of compound does this effect occur ?
Answer: When the unshared pair of electrons around an atom in the middle of a molecule is completely shared by another atom or an ion, it is called lone pair effect. Lone pair effect is shpwn by polar covalent compounds such as HCl and NH₃.

Question 18: (i) Which of the following is not a common characteristic of an electrovalent compound ?
(a) High melting point
(b) Conducts electricity when motten
(c) Consists of oppsitely charged ions
(d) Ionises when dissolved in water
(ii) What are the terms defined below:
(a) A bond formed by a shared pair of electrons with both electrons coming from the same atom.
(b) A bond formed by a shared pair of electrons, each bonding atom contributing one electron to the pair.
Answer: (i) (d)
(ii) (a) Co-ordinate bond. (b) Covalent bond.

Question 19: (i) Acids dissolve in water to produce positively charged ions. Draw the structure of these positive ions.
(ii) Explain why Carbon tetrachloride does not dissolve in water.
(iii) Elements Q and S react together to form an ionic compound. Under normal conditions, which physical state will the compound QS exist in ?
(iv) Can Q and S, both be metals ? Justify your answer.
Answer:
ICSE Solutions for Class 10 Chemistry - Chemical Bonding 7
(ii) Because carbon tetrachloride is non-polar covalent compound whereas water is a polar covalent solvent.
(iii) Solid state.
(iv) No. Because to form an ionic compound if one element gives electrons, the other element should accept electrons. Metals can only lose electrons to provide +ve ions.

Question 20: Predict the type of bonding in the following molecules :
(i) Oxygen (ii) Calcium oxide
(iii) Water (iv) Methane
(v) Ammonium ion (vi) Nitrogen
(vii) Magnesium chloride (viii) Carbon dioxide
(ix) Carbon tetra chloride (xi) Hydrogen cyanide (x) Hydrogen chloride
Answer: (i) Covalent bond (ii) Ionic bond
(iii) Covalent bond (iv) Covalent bond
(v) Covalent bond (vi) Ionic bond
(vii) Covalent bond (viii) Covalent bond
(ix) Covalent bond (xi) Covalent and co-ordinate bonds (x) Covalent bond

Figure/Table Based Questions

Question 1: With the help of the figure, explain that methane molecule is a non-polar covalent compound ?
Answer: A covalent bond between two atoms is non-polar if the electrons involved in bond formation are equally shared between two atoms having similar electronegativities. For example, in case of methane molecule, the four electron pairs shared between one carbon atom and four hydrogen atoms lie exactly in between one carbon atom and four hydrogen atoms and hence forms non-polar bonds.
ICSE Solutions for Class 10 Chemistry - Chemical Bonding 16
The three dimensional structure of methane molecule has the carbon atom at the centre of the tetrahedron and four hydrogen atoms are located at the corners of the tetrahedron. In such a configuration, none of the participating atoms is more electrically charged. So, methane is a non-polar covalent compound.
Electro-negativity of carbon = 2.5 .
Electro-negativity of hydrogen = 2.1

Question 2: With the help of the figure Show HCl is-a polar molecule.
Answer: In HCl molecule the strong nuclear charge of chlorine atom attracts the electron of hydrogen far away from its nucleus, with the result the hydrogen atom develops a slight positive charge (d⁺) and chlorine atom develops a slight negative charge (d^–)
ICSE Solutions for Class 10 Chemistry - Chemical Bonding 17

Question 3: Explain how polar covalent compound HCl which is a bad conductor in pure and liquid state, ionises in water.
Answer: A molecule of HCl is a polar covalent, i.e., the electron pair shared between hydrogen and chlorine is far away from hydrogen than chlorine, with the result that hydrogen atom has a slight positive charge on it and the atom of chlorine has slight negative charge on it as,
ICSE Solutions for Class 10 Chemistry - Chemical Bonding 8
When hydrogen chloride is added to water, then water molecules bombard it from all directions. If the alignment of a water molecule is such that slightly negative oxygen atom faces the slightly positive hydrogen atom of HCl then, the slightly positive hydrogen atom is swallowed by water molecule in the form of single proton to form hydronium ion (H⁺³O). The residual chlorine atom takes away the electron of hydrogen atom along with it so as to form chloride ion as illustrated below:
ICSE Solutions for Class 10 Chemistry - Chemical Bonding 9

Question 4: How does common salt solution ionises in water which is a polar covalent compound ?
Answer: When the sodium chloride crystals come in contact with water, they are bombarded by water molecules from all possible directions.
When the molecules of water bombard the sodium ion, such that the slightly negatively charged oxygen atom face sodium ion, then they exert an electrostatic pull on it. If sufficient number of water molecules strike a particular sodium ion in same fashion, then it can be pulled out of the crystal of sodium chloride to form free sodium ion.
ICSE Solutions for Class 10 Chemistry - Chemical Bonding 10
Similarly, if the molecules of water bombards the chloride ion, such that the slightly positively charged hydrogen atoms face chloride ion then they exert an electrostatic pull on it. If sufficient number of water molecules strike a particular chloride ion in same fashion, then it can be pulled out of the crystal of sodium chloride to form free chloride ion.
Figures (b) and (c) show a sodium ion and a chloride ion has been pulled out of crystalline structure by water molecules. However, it is not actually known that how many molecules of water are necessary to pull out a particular ion from its crystal.

Question 5: Draw dot diagrams to illustrate the structure of the molecules of:
(i) Ammonia (ii) Carbon dioxide
(iii) Methane (iv) Water
Answer:
ICSE Solutions for Class 10 Chemistry - Chemical Bonding 11

Question 6: Give the electron dot structures of:
(i) NaCl (ii) MgCl₂ (iii) CaO (iv) Cl₂ (v) H₂O (iv) NH₃
Answer:
ICSE Solutions for Class 10 Chemistry - Chemical Bonding 13

Question 7: Draw an electron dot diagram to show the structure of hydronium ion. State the type of bonding present in it.
Answer: Formation of hydronium ion:
ICSE Solutions for Class 10 Chemistry - Chemical Bonding 14
The type of bonding present in hydronium ion is co-ordinate bonding.

Question 8: By drawing an electron dot diagram, show the lone pair effect leading to the formation of ammonium ion from ammonia gas and hydrogen ion.
Answer:
ICSE Solutions for Class 10 Chemistry - Chemical Bonding 15
NH₃ has one lone pair of electrons which is donates to hydrogen atom forming a co-ordinate bond. The arrow represents a co-ordinate bond. The arrow points from donor to acceptor atom.

Reasoning Based Questions

Question 1: Why atoms combine with one another ?
Answer: The cause of chemical combination between atoms of the various elements is their tendency to acquire nearest stable noble gas configuration of octet of electrons and duplet of electrons in case of hydrogen atoms in their outermost shells.

Question 2: Why do certain elements form ions ?
Answer: Every particle (molecule, atom or ion) has the tendency to attain the state of lowest energy. As atoms of all elements except the noble gases, have one to seven electrons in their outermost shell, therefore, they are not in the state of minimum energy. They are reactive. In order to attain a minimum state of energy, i.e., to acquire a duplet or octet structure in their valence shell, they either donate or accept electrons. In this process, they become charged particles or ions.

Question 3: Why are all atoms other then noble gas atoms, reactive ?
Answer: Because they are short of octet in their outermost shell. They tend to attain eight electrons in their outermost shell to acquire nearest inert gas electronic configuration.

Question 4: Why a molecule of hydrogen is more stable than the uncombined atoms ?
Answer: When a molecule of hydrogen is formed from the atoms, energy is released (104 kcal/ mol). The molecules possessing lower energy are more stable, than the atoms. Hence molecule of hydrogen is more stable than uncombined atoms.

Question 5: Why is hydrogen ion called proton?
Answer: An atom of hydrogen has one proton in its nucleus and one electron in its valence shell. It donates its valence electron, the residual ion consists of a single proton. It is on account of this fact, that hydrogen ion is called proton.

Question 6: A cation is smaller than the atom from which it is formed. Why ?
Answer: In the formation of a cation, the atom loses the electrons of its outer shell. Thus, the cation has one electron shell less than the atom, from which it is formed. So, it is smaller than the atom.

Question 7: An anion carries negative charge. Why ?
Answer: When an atom forms an anion, it gets one or more electrons (from another atom) in its outer shell. As the number of electrons in the outer shell is increased, the repulsion between them increases. This makes the shell expand outward. Further, since the number of protons remains the same as in the neutral atom, the nucleus attracts the increased number of electrons less strongly. For these reasons the anion is bigger than the parent atom.

Question 8: Why electrovalent compounds form hard crystals ?
Answer: The crystals of electrovalent compounds are made up of crystal lattice containing oppositely charged ions. Each cation is surrounded by a definite number of anions and vice-versa. Their is a great electrostatic force of attraction among these oppositely charged ions and as a result, ionic compounds form hard crystals.

Question 9: Why electrovalent compounds have high melting, boiling points and low volatility ?
Answer: There is a strong force of attraction among the oppositely charged ions in the crystals of electrovalent compounds. Therefore, a large amount of energy is required to separate them. Due to these strong forces of attraction, ionic compounds have high melting and boiling points and low volatility.

Question 10: Why electrovalent compounds in crystalline state do not conduct electricity ?
Answer: Electrovalent crystalline solids do not conduct electricity because the oppositely charged ions in them are held together by a strong electrostatic force of attraction. These ions occupy fixed position in the crystals and do not move when an electric field is applied. .

Question 11: Why do electrovalent compounds usually dissolve in water and molecular compounds dissolve in organic solvents ?
Answer: Water is polar molecule.%It hydrates ions by its polar attraction and pulls the ions apart. In covalent compounds the polar charge on molecules is weak and does not have that much of attractive force on the molecules, organic solvents exert a greater polar attraction on covalent molecules and hence dissolve them.

Question 12: Why ionic compounds are generally soluble in water, but insoluble in organic solvents ?
Answer: The water molecules have high dielectric constant thus, water molecules easily break the ionic bonds between the ions. The ions drift in water in all possible directions and hence, ionic compounds dissolve in water, while organic solvents are non-polar in nature and hence, cannot break the ionic bonds. Thus, the ionic compounds do not dissolve in them.

Question 13: Why molten NaCl conduct electricity but, CCl₄ does not ?
Answer: Molten NaCl contains Na⁺ and Cl^– ions, which are free to move, hence it conducts electricity. Whereas Liquid CCl₄ does not contain any charged particles to conduct electricity.

Question 14: Why is sodium ion (Na⁺) not reactive, but sodium metal is very reactive ?
Answer: Sodium ion has eight electrons in its valency shell and it is the minimum state of energy, while the sodium metal has one electron in valency shell, so the sodium metal is very reactive.

Question 15: Why covalent compounds are generally liquids or gases ?
Answer: In covalent compounds, the molecules are held together by weak Van der Waal’s forces. In liquids, the molecules are weakly attracted whereas in gases, these forces are almost non¬existent. Hence, they are generally liquids or gases.

Question 16: Why all covalent compounds are bad conductor of electricity ?
Answer: The covalent compounds do not have positive or negative ions in their fused state. Thus, when electric potential is supplied, no ions migrate to opposite poles and hence no conduction of electric current takes place.

Question 17: Why covalent compounds have low melting point and boiling point ?
Answer: The force of attraction between the molecules is very weak and so the amount of energy needed to separate them is small, consequently they have low melting points and boiling points.

Question 18: Why most of the covalent compounds have density less than that of water ?
Answer: The covalent molecules are held very weakly by van der Waal’s forces. Thus, there are large inter molecular spaces between the molecules. In other words the number of molecules per unit volume is less. Thus mass per unit is also less and hence, covalent compound have low density.

Question 19: Why do covalent compounds exist as gases, liquids or soft solids ?
Answer: Covalent compounds exists as gases, liquids or soft solids because they have weak forces of attraction between their molecules.

Question 20: Why hydrogen chloride can be termed as a polar covalent compound ?
Answer: Pure covalent bond exists between two elements which have similar electronegativities. In hydrogen chloride, chlorine being more electronegative attracts the shared pair of electrons towards itself. As a result hydrogen acquires partial positive charge and chlorine gets partial r negative charge. Thus, hydrogen chloride can be termed as a polar covalent compound.

Question 21: Why is methane molecule regarded as a non-polar covalent compound ?
Answer: It has been found that a methane molecule has a three dimensional tetrahedral structure. The four carbon hydrogen tetrahedral structure. The four carbon hydrogen bonds are directed towards the four corners of tetrahedron. In such a configuration, none of the participating atoms is more electrically charged as compared to other atoms. Hence methane molecule is a non polar covalent compound.

Question 22: Why the melting and boiling points of co-ordinate compounds are higher than covalent compounds and lower than ionic compounds ?
Answer: A co-ordinate bond is a union of one electrovalent and one covalent bond, the volatility of these compounds lies between that of covalent and ionic compounds. Thus their melting and boiling points are higher than covalent compounds and lower than ionic compounds.

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Chemical Bonding

November 30, 2020November 30, 2020 by Raju

Chemical Bonding

We know that different elements have different atomic numbers and electronic configurations. The properties of atoms depend upon their electronic configurations. Some atoms are more reactive than others. Noble gas (He, Ne, Ar, Kr, Xe and Rn) atoms are not reactive at all; they are inert and stable. Then the question arises why noble gases do not react to form compounds, while other elements do so? This can be answered by comparing the electronic configurations of noble gases with those of other elements. Also, it is important to understand how and why atoms react to form molecules and compounds. Atoms gain electrons in their outermost shells or lose them from their outermost shells, or share electrons with other atoms in such a way that their outermost shells become filled to capacity. They can do this by reacting with other atoms. As long as the outermost shell can accommodate more electrons, i.e., it is not full, an atom tends to combine with other atoms in order to fill its outermost shell. When the outermost shell is filled to capacity, the atom becomes stable.

The atoms of all other elements (elements other than the noble gases) have in their outermost shells less than 8 electrons, i.e., their outermost shells are not filled to capacity. Therefore, the atoms of these elements combine with other atoms to achieve stable configurations like those of the noble gases. It is the tendency on the part of an atom to achieve a stable configuration (like that of the noble gases) which is responsible for its chemical reactivity.

People also ask

Bonds:

We know that an atom tends to attain stability by acquiring the electronic configuration of its nearest noble gas. This can be achieved in anyone of the following manners during chemical combination:
1. By the transfer of electron(s) from one atom to another
2. By the sharing of valence electrons between the two combining atoms
There must be some kind of force which binds the atoms together in a molecule. The attractive force which holds together two atoms, two molecules, two ions or a combination of these is known as a chemical bond.
The two modes of attaining the electronic configuration of the nearest noble gas give rise to two types of bonds-the electrovalent bond and the covalent bond.

The Electrovalent Bond :

In this type of bond, valence electrons are transferred from one atom to another. One atom donates its excess electrons to another atom so that both the atoms may acquire a stable noble gas configuration. The atom which loses electron becomes positively charged and is called the cation. The atom which takes up the electron lost by the first atom becomes negatively charged and is called the anion. These two oppositely charged ions are now held together by an electrostatic force of attraction. This force of attraction binding the two atoms together is known as an electrovalent or ionic bond.
Thus, the chemical bond formed between two atoms by the transfer of one or more valence electrons from one atom to the other is known as an electrovalent or ionic bond. It is also called a polar bond.

Examples: Combination of sodium (Na) and chlorine (Cl) atoms to form sodium chloride (NaCl)
The atomic number of sodium is 11. So its electronic configuration is 2, 8, 1. It has only one electron in its outermost shell. The Na atom transfers this electron and becomes positively charged sodium ion (Na⁺).
Chemical Bonding 1 Thus, the electronic configuration of the Na⁺ ion is the same as that of neon which is the noble gas nearest to sodium in the periodic table.
Let us consider the chlorine atom (Cl). The atomic number of chlorine is 17. So its electronic configuration is 2, 8, 7. It has 7 electrons in its outermost shell. It, thus, lacks 1 electron to acquire a stable noble gas configuration. So a chlorine atom takes 1 electron transferred by the sodium atom and becomes negatively charged chloride ion (Cl^–).
Chemical Bonding 2 Thus, the chloride ion (Cl^–) attains the configuration of the nearest noble gas, argon. [Valence electrons are shown by dots around the symbol.]
The two ions (Na⁺ and Cl^–) being oppositely charged, are now held together by electrostatic force of attraction as Na⁺Cl^–.
Chemical Bonding 3 The formation of sodium chloride can be shown diagrammatically as in figure.
Chemical Bonding 4 The force that holds Na⁺ and Cl^– ions together is called an electrovalent bond. As this bond exists between ions, it is also called an ionic bond. An electrovalent bond is polar, i.e., the positive and negative charges are separated. Compounds containing such bonds are called’ electrovalent, or ionic, or polar compounds.
Note:
(a) In the formula of an ionic compound, the positive ion is written first,
(b) Charges on the ions of an ionic compound are usually not shown with the formula. So, sodium chloride is usually expressed as NaCl, not as Na⁺Cl^–.

Compound	Formula	Ions involved
Sodium chloride	NaCl	Na⁺ and Cl^–
Magnesium chloride	MgCl₂	Mg²⁺ and Cl^–
Magnesium oxide	MgO	Mg²⁺ and O^2–
Calcium chloride	CaCl₂	Ca²⁺ and Cl^–
Calcium oxide	CaO	Ca²⁺ and O^2–
Ammonium chloride	NH₄Cl	NH₄⁺ and Cl^–
Barium chloride	BaCl₂	Ba²⁺ and Cr
Potassium nitrate	KNO₃	K⁺ and NO₃^–
Ammonium sulphate	(NH₄)₂SO₄	NH₄⁺and SO₄^2-
Cupric sulphate	CuSO₄	Cu²⁺ and SO₄²⁺
Cupric chloride	CuCl₂	Cu²⁺ and Cl^–

Electrovalency :
When an element forms electrovalent bond, its valency is known as electrovalency.
The number of electrovalent or ionic bonds an atom can form is called its electrovalency. The electrovalency of an element is, therefore, equal to the number of electrons lost or gained by the atom to form an ion.
Elements which lose electrons show positive electrovalency and those which gain electrons show negative electrovalency. For example, in the formation of sodium chloride (Na⁺Cl^–), the electrovalency of sodium (Na) is +1, while that of chlorine (Cl) is – l.
Elements which lose or gain one, two, three, … , etc., electrons are said to be monovalent (or univalent), divalent (or bivalent), trivalent, … , etc., respectively.
Monovalent elements : Na, CI, F
Divalent elements : Mg, Ca, Ba, O
Trivalent elements : Al, B
Characteristics of electrovalent or ionic compounds :

Electrovalent compounds are made up of positively and negatively charged ions. For example, sodium chloride (NaCl) is made up of Na⁺ and Cl^– ions arranged in a definite order in three dimensions to form crystals.
Electrovalent compounds have high melting and boiling points. This is due to the presence of strong electrostatic forces of attraction between the positive and negative ions. A large amount of heat energy is required to break this force of attraction. Hence, the melting and boiling points of electrovalent compounds are high.
Electrovalent compounds are usually soluble in water but insoluble in organic solvents such as benzene, acetone, carbon disulphide and carbon tetrachloride.
Electrovalent compounds conduct electricity in molten state and in their aqueous solutions.

In solid electrovalent compounds the ions are held together in fixed positions and cannot move. Hence, such compounds in the solid state do not conduct electricity.
When an electrovalent compound is dissolved in water or is melted, the crystal structure breaks down. The ions now become free to move and can, therefore, conduct electricity.
That the ionic compounds in molten state or in solution become conductors of electricity.