Chemical Bonding Solutions for ICSE Board Class 10 Science

Intext Questions 

1. How do atoms attain noble gas configuration?

Ans: To attain noble gas configuration, atoms share, lose or gain electrons.

2. Define

(a) a chemical bond

Ans: A chemical bond can be defined as the force of attraction between any two atoms in a molecule that keeps the molecule stable.

(b) an electrovalent bond

Ans: Electrovalent bond is defined as the bond formed between the two atoms by the transfer of one or more electrons from an electropositive atom to an electronegative atom.  An electrovalent bond is also known as an ionic bond.

(c) a covalent bond

Ans: Covalent bond is formed due to the sharing of electrons.

3. What are the conditions for the formation of an electrovalent bond?

Ans: Conditions for the formation of electrovalent bond-

1. Atoms that form cations should have 1, 2, or 3 electrons in their valence shell while the atoms forming anions should have 5, 6, or 7 electrons in their valence shell.

2. There should be a high electronegativity difference between the atoms.

3. Atom forming cations should have low ionization enthalpy i.e less energy required to remove electrons from the valence shell. Atoms forming anions should have a high electron affinity to gain the electron. There should be a net release of energy.

4. There should be high lattice enthalpy.

4. An atom X has three electrons more than a noble gas configuration. What type of ion will it form? Write the formula of its (i) Sulphate (ii) Nitrate (iii) Phosphate (iv) carbonate (v) Hydroxide

Ans: It will form a cation: M3+

Sulphate: M2(SO4)3 

Nitrate: M(NO3)3 

Phosphate: M3(PO4)3 

Carbonate: M2(CO3)3 

Hydroxide: M(OH)3 

5. Mention the basic tendency of an atom that makes it combine with other atoms.

Ans: Atoms combine with other atoms to form a noble gas configuration.

6. The element X has an electronic configuration of 2,8,18,8,1. Without identifying X

1. Predict the sign and charge on a sample ion of X.

Ans: Element X has the electronic configuration 2,8,18,8,1 and so has a tendency to lose one electron and complete an octet, resulting in the formation of an X+ ion with a charge of +1 in general.

2. Write whether X will be an oxidising agent or reducing agent and why?

Ans: X will be a reducing agent because it has the tendency to form cation.

7. In the formation of compound XY2, an atom X gives one electron to each Y atom, what is the nature of the bond in XY2? Draw the electron dot structure of this compound?

Ans: Ionic bonds will form between X and Y.

8. An atom has 2, 8, 7 electrons in its shell. It combines with Y having 1 electron in its outermost shell.

(a) What type of bond will be formed between X and Y?

Ans: Ionic bond

(b) Write the formula of the compound formed.

Ans: XY

9. Explain with the help of the ionic equation and electron dot structural diagram the formation of the following electrovalent compounds.

(i) NaCl 

Ans: 

(ii) MgCl2

(iii) CaO

10. Compare:

(a) Sodium atom and sodium ion

(b) Chlorine atom and chlorine ion

With respect to

(i) Atomic structure

(ii) Electrical state

(iii) Chemical action and

(iv) toxicity

Ans: a.

(b) Chlorine atom and chlorine ion

11. The electronic configuration of fluoride ions is the same as that of a neon atom. What is the difference between the two?

Ans: Fluorine atoms gain one electron to form fluoride ions or to attain noble gas configuration. So fluorine ions are negatively charged while neon is neutral.

12. State which of the following are reduction reactions and which are oxidation

(i)  Pb2+ + 2e- → Pb 

Ans: Reduction reaction (As this reaction shows the gain of electrons).

(ii)  Fe2+ - e- → Fe3+

Ans: Oxidation reaction (As this reaction shows the loss of electron).

(iii) A3+ + e-1→ A2+ 

Ans: Reduction reaction (As this reaction shows the gain of electrons).

(iv) Cu → Cu2+ + 2e-  

Ans: Oxidation reaction (As this reaction shows the loss of electrons).

13. What do you understand about redox reactions? Explain oxidation and reduction in terms of loss or gain of electrons.

Ans: Redox reactions are defined as the reactions where oxidation and reduction takes place simultaneously. 

Oxidation is defined as the loss of electrons while reduction is defined as the gain of electrons.

14. Divide the following redox reactions into oxidation and reduction half-reactions.

i. Zn+Pb2+→Zn2++Pb

Ans: Zn→Zn2++2e- (Oxidation)

Pb2++2e-→Pb (Reduction) 

ii. Zn+Cu2+→Zn2++Cu

Ans: Zn→Zn2++2e- (Oxidation)

Cu2++2e-→Cu (Reduction)

iii. Cl2+2Br-→Br2+2Cl-

Ans: Cl2+2e-→2Cl- (Reduction)

2Br-→Br2+2e- (oxidation)

iv. Sn2++2Hg2+→Sn4++Hg22+

Ans: Sn2+→ Sn4+ + 2e- (Oxidation)

2Hg2+ + 2e-→ Hg2 (Reduction)

v. 2Cu+→Cu+Cu2+

Ans: Cu+→ Cu2+ + e- (Oxidation)

Cu+ + e- →Cu (Reduction) 

15. Potassium (Atomic No. 19) and chlorine (Atomic No. 17) react to form a compound. On the basis of electronic concept, explain

i. Oxidation

Ans: Potassium undergoes oxidation as it loses an electron.

ii. Reduction

Ans: Chlorine undergoes reduction as it gains an electron.

iii. oxidising agent

Ans: Chlorine acts as an oxidising agent. 

iv. Reducing agent

Ans: Potassium acts as a reducing agent

Intext Questions 

1. What are the conditions necessary for the formation of covalent molecules?

Ans: Both atoms, i.e. non-metals, should have four or more electrons in their outermost shells. 

(ii) The electronegativity of both atoms should be high.

(iii) The electron affinity and ionisation potential of both atoms should be high.

(iv) The difference in electronegativity between the two atoms should be zero or minimal. 

(v) The atoms proximity to one another should be followed by a decrease in energy.

2. Elements A, B, and C have atomic numbers 17, 19, and 10 respectively.

(a) State which one is:

(i) A non-metal

Ans: A is a non metal. 

(ii) A metal

Ans: B is a metal

(iii) Chemically inert?

Ans: C is chemically inert

(b) Write down the formula of the compound formed by two of the above elements.

Ans: AB

3. Draw the electron dot diagram and structure of:

a. nitrogen molecule

Ans: 

b. magnesium chloride

Ans: 

c. methane

Ans: 

4. What is the difference between:

(a) Ionic compounds and polar covalent compounds

Ans:

(b) Ionic compounds and covalent compounds

Ans: 

(c) A polar covalent compound and a nonpolar covalent compound?

Ans: 

5. A solid is crystalline, has a high melting point and is water soluble. Describe the nature of the solid.

Ans: Because the oppositely charged ions are bound closely together by strong intermolecular forces of attraction, the solid is ionic in nature, which explains its high melting point and water solubility.

6. What do you understand about dipole (polar) compounds? Explain it by taking hydrogen chloride as an example.

Ans: A dipole molecule possesses a slight positive as well as a slight negative charge. Hydrogen has a small positive charge in HCl, while chlorine has a slight negative charge. The dipole moment of the HCl molecule is 1.03 D, which is written as:

7. a. Explain the bonding in methane molecules using the electron dot structure.

Ans: 

b. The methane molecule is a nonpolar molecule. Explain.

Ans: Methane is a nonpolar molecule as electrons are equally distributed between carbon and hydrogen so there is no charge separation and hence the atom is electrically neutral and symmetrical.

8. Give the characteristic properties of:

(a) Electrovalent compounds

Ans:

1. They possess electrovalent linkage, which is formed by the movement of electrons from one atom to another; these compounds only have one bond.

2. The majority of electrovalent substances exist in solid form. They have a high melting and boiling point.

3. They are soluble in water but insoluble in organic solvents such as benzene, ether, and others.

4. Ions make up the crystals of electrovalent substances.

5. In solution and molten state, they are good conductors of electricity.

6. They are very polar and ionise when exposed to water. 

KCl → K++ Cl-

(b) Covalent compounds

Ans: 

1. They have a covalent bond produced by the mutual sharing of electrons between the two atoms. These mixtures contain single, double, and triple bonds.

2. Solid, liquid, and gaseous phases are the most common states for covalent compounds. They are volatile and soft.

3. They are soluble in organic solvents but in water they are insoluble or only slightly soluble.

4. Molecules make up the crystals of covalent compounds.

5. In solution, as well as in molten or fusion states, they are poor conductors of electricity.

6. These compounds frequently have low melting and boiling points.

9.  a. State the type of bond is formed when the combining atoms have:

i. zero E.N. difference 

Ans: Non polar covalent

ii. small E.N. difference  

Ans: Polar covalent

iii. large E.N. difference

Ans: Ionic bond

b. State the type of bond formed and draw Lewis structure of 

i. water     

Ans: Covalent bond 

ii. calcium oxide

Ans: Ionic bond

10. Explain the following:

a. Electrovalent compounds conduct electricity.

Ans: Electrovalent compounds in the fused or aqueous state are good conductors of electricity because electrostatic forces of attraction between ions in the solid state are very strong, whereas these forces weaken in the fused or aqueous state. As a result, ions become mobile.

b. Electrovalent compounds have a high melting point and boiling point, while covalent compounds have low melting and boiling points.

Ans: The atoms of covalent compounds are tightly linked to each other, but the molecules are not very strongly attracted to other molecules in the compound. Electrovalent compounds, on the other hand, have atoms (ions) that have a significant attraction to other ions in their vicinity. For covalent solids, this results in low melting temperatures, while for electrovalent solids, it results in high melting points.

c. Electrovalent compounds dissolve in water, whereas covalent compounds do not.

Ans: The ions of electrovalent compounds interact with polar water mo;ecule which makes them dissolve in water whereas covalent compounds do not contain ions which makes them water insoluble.

d. Electrovalent compounds are usually hard crystals yet brittle.

Ans: Electrovalent compounds are often hard crystals that seem to be brittle due to strong electrostatic forces of attraction between their ions that make them difficult to separate.

e. Polar covalent compounds conduct electricity.

Ans: They conduct electricity due to the presence of free ions in molten state.

f. Water is a polar covalent molecule.

Ans: Because of the unequal distribution of electrons among the atoms and the molecule's asymmetrical form, a water molecule has two poles: a positive charge on the hydrogen pole (side) and a negative charge on the oxygen pole(side).

11. Elements X, Y, and Z have atomic numbers 6, 9, and 12, respectively. Which one 

a. forms an anion

Ans: Y will form an anion

b. forms a cation

Ans: Z will form a cation

c. State the type of bond between Y and Z and give its molecular formula.

Ans: ZY2

12. Taking MgCl2 as an electrovalent compound and CCl4 as a covalent compound, gives four differences between electrovalent and covalent compounds.

Ans: 

13. Potassium chloride is an electrovalent compound, while hydrogen chloride is a covalent compound. But both conduct electricity in their aqueous solution. Explain 

Ans: Because the electrostatic forces of attraction weaken in the fused state or in aqueous solution, potassium chloride is an electrovalent chemical that transmits electricity in the molten state.

Hydrogen chloride, for example, is a polar covalent molecule that ionises in solution and can behave as an electrolyte. In their aqueous solutions, both can conduct electricity.

14. a. Draw the electron dot structure of covalent compound methane (non-polar) and HCl (polar) and give two differences between them.

Ans: Structure of methane 

Electron dot structure of HCl

Difference between methane and HCl

b. Name two compounds that are covalent when taken pure but produce ions when dissolved in water.

Ans: Hydrochloric acid and ammonia are the two covalent compounds. They are covalent in pure state but when dissolved in water, they generate ions.

c. For each compound mentioned above give the formulae of ions formed in aqueous solution.

Ans: HCl + H2O → H3O+ + Cl- 

NH3 + H2O → NH4+ + OH- 

15. An element M burns in oxygen to form an ionic bond MO. Write the formula of the compounds formed if this element is made to combine with chlorine and sulphur separately.

Ans: Since M combines with O to form MO so its valency will be +2. 

Formula with chlorine- MCl2

Formula with sulphur- MS

16. Element A has 2 electrons in its M shell. Element B has the atomic number 7.

(a) Write equations to show how A and B form ions.

Ans: A→A2++2e-

B+3e-→B3-

(b) If B is a diatomic gas, write the equation for the direct combination of A and B to form a compound.

Ans: 6A+2B2→2A3B2

(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 _________ and B at the ________ of the electrolytic cell. 

Ans: Cathode, Anode 

Exercise Questions

1. Define a coordinate bond and give conditions for its formation.

Ans: A coordinate bond is a bond established between two atoms by sharing a pair of electrons that are provided totally by one of the combining atoms but shared by both. It's illustrated by an arrow that starts with the donor atoms and ends with the acceptor.

Conditions: 

1. At least one lone pair of electrons must exist in one of the two atoms.

2. At least one lone pair of electrons should be missing from another atom.

The two lone pairs of electrons in the oxygen atom of water are used to create a coordination bond with the hydrogen ion, which is lacking an electron, resulting in the hydronium ion.

2. What do you understand about a lone pair of electrons?

Ans: A lone pair of electrons is a pair of electrons that are not shared with any other atom. It is given to the other atom in order to build a coordinate bond.

3. State the type of bonding in the following molecules:

a. Water

Ans: Polar covalent bond

b. Calcium oxide

Ans: Ionic bond

c. Hydroxyl ion

Ans: O and H possess a single covalent bond

d. Methane

Ans: Covalent bond

e. Ammonium ion

Ans: Coordinate bond 

f. Ammonium chloride

Ans: Electrovalent bond, dative bond (or coordinate bond) and covalent bond

4. (a) Draw an electron dot diagram to show the structure of each of the following:

(i) Hydronium ions

Ans: 

(ii) Ammonium ion

Ans:

(iii) Hydroxyl ion

Ans: 

(b) Give two examples in each case:

(i) Co-ordinate bond compounds

Ans: Ammonium Ion and hydronium ion

(ii) Solid covalent compounds

Ans: Phosphorus pentachloride and diamond

(iii) Gaseous polar compounds

Ans:  Hydrogen chloride and water vapour

(iv) Gaseous non-polar compounds

Ans: Oxygen gas and nitrogen gas

(v) Liquid non-polar compounds

Ans: Toluene and Gasoline

5. Element M forms a chloride with the formula MCl2 which is a solid with high melting point. M would most likely be in the group in which ______ is placed. 

(a) Na (b) Mg (c)Al (d) Si

Ans: (b)Mg

6. Complete the following:

Ans: 

7. a. How many atoms of each kind are present in the following molecules: calcium oxide, chlorine, water, carbon tetrachloride?

Ans:  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

b. How many electrons are required by each atom mentioned in (a) to attain the nearest noble gas configuration?

Ans: 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 electron pairs with hydrogen forming covalent bonds.

H - will donate one electron by sharing an electron pair with carbon.

8. Complete the following:

(a) When the nuclei of two reacting atoms are of _____ mass, then a bond so formed is called _____covalent bond. (Equal, unequal, polar, non -polar).

Ans: Unequal, polar

(b) In case of non-polar covalent bond, the covalent bond is formed in the _____of atoms and shared electrons are distributed _____. (Corner, middle, equally, unequally).

Ans: Middle, equally

(c) Ionic or electrovalent compounds do not conduct electricity in their …………… state. (Fused/solid)

Ans: Solid 

(d) The ions in ______ compounds are held very strongly due to strong _______ forces. (electrovalent, covalent, electromagnetic, electrostatic)

Ans:  Electrovalent, electrostatic

9. a. Compound X consists of molecules. 

Choose the letter corresponding to the correct answer from the options A, B, C and D given below:

i. The type of bonding in X will be

A. ionic

B. electrovalent

C. covalent

D. molecular

Ans: (C) covalent

ii. X is likely to have a

A. low melting point and high boiling point

B. high melting point and low boiling point

C. low melting point and low boiling point

D. high melting point and high boiling point

Ans: (C) low melting point and low boiling point

iii. In the liquid state, X will

A. become ionic

B. be an electrolyte

C. conduct electricity

D. not conduct electricity

Ans: (D) not conduct electricity

10. a. Electrons are getting added to an element Y:

i. Is Y getting oxidised or reduced?

Ans: Reduced 

ii. What charge will Y migrate to during the process of electrolysis?

Ans: Y will migrate to cathode 

b. Acids dissolve in water and produce positively charged ions. Draw the structure of these positive ions.

Ans: Structure of hydronium ion:

c. Explain why carbon tetrachloride does not dissolve in water.

Ans: It is a nonpolar covalent molecule and hence does not dissolve in water.

11. a. Elements Q and S react together to form an ionic compound. Under normal conditions, which physical state will the compound QS exist in?

Ans: QS will exist in solid state at normal conditions as they react together to form an ionic compound.

b. Can Q and S both be metals? Justify your answer.

Ans: No they both can't be metals because formation of ionic bond takes place between metals and non-metal where the electron lost by metal is accepted by non-metal. 

c. The property which is characteristic of an electrovalent compound is that:

A. It is easily vaporized

B. It has a high melting point

C. It is a weak electrolyte 

D. It often exists as liquid 

Ans: B. It has a high melting point

d. When a metal atom becomes an ion 

A. It loses electron and gets oxidized

B. It gains electron and is reduced 

C. It gains electron and gets oxidized 

D. It loses electron and is reduced  

Ans: A. It loses electron and gets oxidized

12. a. In the formation of magnesium chloride (by direct combination between magnesium and chloride), name the substance that is oxidized and the substance that is reduced.

Ans: Magnesium oxidises and chlorine reduces during the formation of magnesium chloride.

b. What are the terms defined below?

(i) A bond formed by a shared pair of electrons, each bonding atom contributing one electron to the pair.

Ans: Covalent bond

(ii) A bond formed by a shared pair of electrons with both electrons coming from the same atom.

Ans: Coordinate bond 

2009

a. The one which is composed of all the three kinds of bonds (ionic, covalent and coordinate bonds) is

A. Sodium chloride

B. Ammonia

C. Carbon tetrachloride

D. Ammonium chloride

Ans:  D. Ammonium chloride

b. Draw the structural formula of carbon tetrachloride and state the type of bond present in it.

Ans: 

A single covalent bond is present.

2010

a. Select the correct answer from A, B, C and D. Metals lose electrons during ionisation _____. This change is called

A. Oxidation

B. Reduction

C. Redox

D. Displacement

Ans: A. Oxidation

b. Select the right answer.

i. Sodium chloride _______ covalent bond / ionic bond / covalent and coordinate bond.

Ans: Ionic bond

ii. Ammonium ion _______ covalent bond / ionic bond / covalent and coordinate bond.

Ans: Covalent and coordinate bond

iii. Carbon tetrachloride _______ covalent bond / ionic bond / covalent and coordinate bond.

Ans: Covalent bond

2011

a. i. In covalent compounds, the bond is formed due to …………… (sharing/ transfer) of electrons.

Ans: Sharing

ii. Electrovalent compounds have a ……….. (low/high) boiling point.

Ans: High

iii. A molecule of ……………. contains a triple bond. (hydrogen, ammonia, nitrogen).

Ans: Nitrogen

b. By drawing an electron dot diagram, show the lone pair effect leading to the formation of ammonium ions from ammonia gas and hydrogen ion.

Ans: 

c. Give reasons. Hydrogen chloride can be termed a polar covalent compound.

Ans: HCl is a covalent compound as the bond is formed between hydrogen and chlorine by sharing of electrons. Since chlorine is more electronegative than hydrogen, chlorine has the tendency to attract a shared pair of electrons towards itself giving chlorine a partial negative charge and hydrogen a partial positive charge leading to the formation of polar covalent bonds.

2012

a. Draw an electron dot diagram of the structure of hydronium ion. State the type of bonding present in it.

Ans: 

Covalent and coordinate bond

b. There are three elements E, F, G with atomic number 19, 8 and 17, respectively. Give the molecular formula of the compound formed between E and G and state the type of chemical bond in this compound.

Ans: E = 19

F = 8

G= 17

Molecular formula: EG

Chemical bond: Ionic bond

2013 

a. A chemical term for a bond formed by a shared pair of electrons with both electrons coming from the same atom.

Ans: Coordinate or dative bond 

b. Among the compounds, identify the compound that has all three bonds - ionic, covalent and coordinate bond.

A. Ammonia

B. Ammonium chloride

C. Sodium hydroxide

D. Calcium chloride

Ans: B. Ammonium chloride

c. State which is not a typical property of an ionic compound.

A. High m.p.

B. Conducts electricity in molten and aqueous state

C. Are insoluble in water

D. Exist as oppositely charged ions even in the solid state

Ans: C. Are insoluble in water

d. Compare carbon tetrachloride and sodium chloride with regard to solubility in water and electrical conductivity.

Ans: 

2014

a. Compound 'X' consists of only molecules. 'X' will have ______

A. Crystalline hard structure

B. A low m.p. and low b.p.

C. An ionic bond

D. A strong force of attraction between its molecules

Ans: B. A low m.p. and low b.p.

b. The molecule which contains a triple covalent bond is

A. ammonia

B. methane

C. water

D. nitrogen

Ans: D. nitrogen

c. Give one word or phrase for the following: Formation of ions from molecules.

Ans: Ionisation 

d. Give reason why covalent compounds exist as gases, liquids or soft solids.

Ans: These exist as gases or liquids or soft solids because they have weak forces of attraction between their molecules.

2016

a) The following table shows the electronic configuration of the elements W, X, Y, Z:

Answer the following questions based on the table above:

(i) What type of Bond is formed between:

1. W and X

Ans: W will lose one electron while X will gain one electron to attain noble gas configuration. Hence ionic bonds will form between W and X.

2. Y and Z

Ans: Z and Y required one electron to attain stable configuration. Hence covalent bond is formed between Y and Z.

(ii) What is the formula of the compound formed between:

1. X and Z  

Ans: ZX

2. W and X

Ans: XW

Chemistry

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