Chemical Bonding Selina Concise Chemistry Class 10

Selina Concise Chemistry Class 10

Chemical Bonding

Exercise Intext 1

1.How do atoms attain noble gas configuration?

Solution 1.

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

2.Define

(a) a chemical bond

(b) an electrovalent bond

(c) a covalent bond

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 is called as a covalent bond.

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

Solution 3.

Conditions for formation of Ionic bond are:

1. 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.
2. A high difference of electronegativity of the two atoms is necessary for the formation of an Ionic bond.
3. 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.
4. Higher the lattice energy, greater will be the case of forming an ionic compound.

4.An atom M has three electrons more than 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

Solution 4.

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

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

Solution 5.

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

6.

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.

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

Solution 7.

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?

(b) Write the formula of compound formed.

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.

9.Draw electron dot diagrams of

(i) CaO    (ii) NaCl (iii) MgCl_2.

Solution 9.

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

Solution 10.

(a) Sodium atom and sodium ion

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

(b) Chlorine atom and chlorine ion

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

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

Solution 11.

Fluoride ion is negatively charged while neon atom is neutral.

12.a. What do you understand by redox reactions? Explain oxidation and reduction in terms of loss or gain of electrons.

b. Divide the following redox reactions into oxidation and reduction half reactions.

  

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

 i. oxidation

 ii. reduction

 iii. oxidising agent

 iv. reducing agent

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)
1. Zn → Zn2+ + 2e– (Oxidation)
Pb2+ + 2e–  → Pb (Reduction)
2. Zn → Zn2+ + 2e– (Oxidation)
Cu2+ + 2e–→ Cu (Reduction)
3. Cl2 + 2e–→ 2Cl– (Reduction)
2Br–→ Br2 + 2e– (Oxidation)
4. Sn2+→ Sn4+ + 2e– (Oxidation)
2Hg2+ + 2e–→ Hg2 (Reduction)
5. Cu+→ Cu2+ + e– (Oxidation)
Cu+ + e– → Cu (Reduction)
(c)
2K + Cl2→2KCl

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

2. Reduction: In the electronic concept, the reduction is a process in which an atom or ion accepts electron(s).
Cl2 + 2e–→ 2Cl–

3. 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–

4. 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

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

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.

2.Elements A, B and C have atomic numbers17, 19 and 10 respectively.

(a) State which one is:

(i) A non-metal

(ii) A metal

(iii) Chemically inert?

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

Solution 2.

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

3.

Solution 3.

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

3(2017).Draw the electron dot diagram and structure of:

a. nitrogen molecule

b. magnesium chloride

c. methane

Solution 3(2017).

4.What is the difference between:

(a) Ionic compounds and polar covalent compounds

(b) Ionic compounds and covalent compounds

(c) A polar covalent compound and a non-polar covalent compound?

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.

5.The element X has electronic configuration 2, 8, 18, 8, 1. Without identifying X ,

(a) Predict the sign and charge on a simple ion of X

(b) Write if X will be an oxidizing agent or reducing agent and why?

Solution 5.

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

6.What do you understand by polar covalent compounds? Explain it by taking hydrogen chloride as an example.

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.

7.

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.

8.a. Explain the bonding in methane molecule using the electron dot structure.

b. The methane molecule is a non-polar molecule. Explain.

Solution 8.

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.

9.Give the characteristic properties of:

(a) Electrovalent compounds

(b) Covalent compounds

Solution 9.

(a) Properties of Ionic Compounds:

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

(b) Properties of Covalent Compounds:

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

10.

Solution 10.

(a)

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

(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.

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

 i. zero E.N. difference 

 ii. small E.N. difference     

 iii. large E.N. difference

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

  i. water     

 ii. calcium oxide

Solution 11.

12.

Solution 12.

(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.

13.

Solution 13.

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:

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

a. forms an anion

b. forms a cation

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

Solution 14.

a.
i. Y = 9
ii. Z = 12
b. Ionic bond with molecular formula ZY2.

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

Solution 15.

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

Solution 16.

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.

17.a. Name two compounds that are covalent when pure but produce ions when dissolved in water.

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

Solution 17.

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

18.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.

Solution 18.

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

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

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

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

(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. 

Solution 19.

(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 2

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

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:

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.

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.

2.What do you understand by lone pair and shared pair?

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.

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

a. Water

b. Calcium oxide

c. Hydroxyl ion

d. Methane

e. Ammonium ion

f. Ammonium chloride

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

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

(i) Hydronium ions

(ii) Ammonium ion

(iii) Hydroxyl ion

State the type of bonding present in them.

(b) Give two examples in each case:

(i) Co-ordinate bond compounds

(ii) Solid covalent compounds

(iii) Gaseous polar compounds

(iv) Gaseous non-polar compounds

(v) Liquid non-polar compounds

Solution 4.

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]

Solution 5.

Mg

6.Complete the following:

	Sodium	Phosphorus	Carbon
Formula of chloride
Nature of bonding
Physical state of chloride

Solution 6.

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

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

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
b.
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.

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).

(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).

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

Solution 8.
(a) Unequal, polar
(b) Middle, equally
(c) 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

 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

 iii. In the liquid state, X will

A. become ionic

B. be an electrolyte

C. conduct electricity

D. not conduct electricity

b. Electrons are getting added to an element Y:

i. Is Y getting oxidised or reduced?

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

Solution 9.

a.
1. C
2. C
3. D
b.
1. Y is getting reduced.
2. Y is positive and it will migrate towards negative electrode that is cathode.

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

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

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

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

e. The property which is characteristic of an electrovalent compound is that

A. it is easily vaporised

B. it has a high melting point

C. it is a weak electrolyte

D. it often exists as a liquid

f. When a metal atom becomes an ion,

A. it loses electrons and is oxidised

B. it gains electrons and is reduced

C. it gains electrons and is oxidised

D. it loses electrons and is reduced

Solution 10.

1(2004).

Solution 1 (2004).

1(2005).

Solution 1 (2005).

(a) (i) C (ii) C (iii) D
(b) (i)reduced (ii) negative
(c) (i) H3O+ ions

(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.

1(2006).

Solution 1 (2006).

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

1(2007).
(iv) 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.

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

1(2008).(a)
(b)What are the terms defined below?

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


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

Solution 1 (2008).

(a)
(i) D
(b)
(i) Covalent bond
(ii) Coordinate bond.

1(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

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

Solution 1 (2009).

1(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

b. Select the right answer.

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

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

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

Solution 1 (2010).

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

1(2011).a.  

 i. In covalent compounds, the bond is formed due to …………… [sharing/transfer] of electrons.

 ii. Electrovalent compounds have a ……….. [low/high] boiling point.

 iii. A molecule of ……………. contains a triple bond. [hydrogen, ammonia, nitrogen].

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

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

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.

1(2012).a. Draw an electron dot diagram of the structure of hydronium ion. State the type of bonding present in it.

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.

Solution 1 (2012).

1(2013).

Solution 1 (2013).

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

1(2014).

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.