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Chapter 2

Chemical Bonding

Class 10 - Concise Chemistry Selina



Intext Questions 1

Question 1

How do atoms attain noble gas configuration ?

Answer

Atoms attain noble gas configuration by losing, gaining or sharing of electrons present in their outermost shell.

Question 2

Define :

(a) a chemical bond,

(b) an electrovalent bond,

(c) a covalent bond.

Answer

(a) Chemical Bond — A chemical bond may be defined as the force of attraction between any two atoms, in a molecule, to maintain stability.

(b) Electrovalent (or ionic) Bond — 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 is called an electrovalent (or ionic) bond.

(c) Covalent Bond — The chemical bond that is formed between two combining atoms by mutual sharing of one or more pair of electrons is called a covalent bond.

Question 3

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

Answer

The conditions for the formation of an electrovalent bond are:

  1. Low ionisation potential — If the ionisation potential of a particular atom is low, it will lose electron(s) easily, i.e., a cation is formed easily.
  2. High electron affinity — If the electron affinity value is high, anion will be formed easily.
  3. Large electronegativity difference — If the difference in the electronegativities of two elements is higher, then the transfer of electrons will be easier.

Question 4

An atom X has three electrons more than the 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.

Answer

Since there are three electrons more than the noble gas configuration in the atom so the atom will try to lose three electron to gain noble gas configuration. Therefore, it will form a cation X3+.

Formula of its:

(i) Sulphate — X2(SO4)3

(ii) Nitrate — X(NO3)3

(iii) Phosphate — XPO4

(iv) Carbonate — X2(CO3)3

(v) Hydroxide — X(OH)3

Question 5

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

Answer

The basic tendency of an atom which makes it to combine with other atoms is the tendency of elements to acquire the nearest noble gas configuration in their outermost orbit and become stable.

Question 6

The element X has the 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 oxidising agent or a reducing agent and why.

Answer

(a) X+ Reason — Since the element X has 1 electron in its valence shell. So, it will lose an electron and gain noble gas configuration. Therefore it forms a cation (X+). The sign is positive and the charge is of 1 proton.

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

Question 7

In the formation of the 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.

Answer

Since the atom X gives one electron to each Y atom. Therefore, X & Y form an ionic bond in XY2. The electron dot structure of this compound is shown below:

In the formation of the 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. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

Question 8

An atom X 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 the compound formed .

Answer

(a) Ionic Bond
Reason — Since 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 is XY.

Question 9

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

(a) NaCl

(b) MgCl2

(c) CaO

Answer

(a) Na+ + Cl- ⟶ NaCl

The electron dot structural diagram is:

Draw the electron dot structure of Sodium chloride. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

(b) Mg+2 + 2Cl- ⟶ MgCl2

The electron dot structural diagram is:

Draw an electron dot diagram to show the formation of Magnesium chloride. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

(c) Ca+2 + O-2 ⟶ CaO

The electron dot structural diagram is:

Draw the electron dot structure of Calcium oxide. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

Question 10

Compare :

(a) sodium atom and sodium ion

(b) chlorine atom and chloride ion

with respect to

  1. atomic structure
  2. electrical state
  3. chemical action
  4. toxicity

Answer

(a) Comparison between sodium atom and sodium ion:

PropertySodium AtomSodium Ion
Atomic StructureIt has one electron in M shell.It has 8 electrons in L shell.
Electrical StateIt is neutral.It is positively charged.
Chemical ActionIt is very Active.It is inactive.
ToxicityIt is poisonous.It is non-poisonous.

(b) Comparison between chlorine atom and chloride ion:

PropertyChlorine AtomChloride Ion
Atomic StructureIt has 7 electrons in M shell.It has 8 electrons in M shell.
Electrical StateIt is neutral.It is negatively charged.
Chemical ActionIt is very Active.It is inactive.
ToxicityIt is poisonous.It is non-poisonous.

Question 11

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

Answer

The electronic configuration of Fluoride ion is the same as that of a neon atom i.e., both have 8 electrons in their valence shell but Fluoride attain that configuration by gaining an electron so it is negatively charged but neon atom have its own 8 valence electrons so it is neutral i.e., it have no charge on it.

Question 12

State which of the following are reduction reaction and which are oxidation

(i) Pb ⟶ Pb2+ + 2e-

(ii) Fe2+ - e- ⟶ Fe3+

(iii) A3+ + e- ⟶ A2+

(iv) Cu ⟶ Cu2+

Answer

(i) Oxidation, since there is a loss of 2 electrons by Lead (Pb).

(ii) Oxidation, since there is a loss of an electron by Iron (Fe).

(iii) Reduction, since there is a gain of an electron by A.

(iv) Oxidation, since there is a loss of 2 electrons by Copper (Cu).

Question 13

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

Answer

Redox Reaction — A reaction in which oxidation and reduction occur simultaneously is called an oxidation-reduction reaction or redox reaction.

In redox reaction there is a transfer of electrons between two atoms.

The reaction in which electron(s) is gained is called a reduction reaction and the reaction in which there is a loss of electron(s) is called an oxidation reaction.

Question 14

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

(i) Zn + Pb2+ ⟶ Zn2+ + Pb

(ii) Zn + Cu2+ ⟶ Zn2+ + Cu

(iii) Cl2 + 2Br- ⟶ Br2 + 2Cl-

(iv) Sn2+ + 2Hg2+ ⟶ Sn4+ + Hg22+

(v) 2Cu+ ⟶ Cu + Cu2+

Answer

(i) Oxidation : Zn ⟶ Zn2+
    Reduction : Pb2+ ⟶ Pb

(ii) Oxidation : Zn ⟶ Zn2+
    Reduction : Cu2+ ⟶ Cu

(iii) Oxidation : 2Br- ⟶ Br2
    Reduction : Cl2 ⟶ 2Cl-

(iv) Oxidation : Sn2+ ⟶ Sn4+
    Reduction : 2Hg2+ ⟶ Hg22+

(v) Oxidation : Cu+ ⟶ Cu2+
    Reduction : Cu+ ⟶ Cu

Question 15

Potassium (at No. 19) and chlorine (at No.17) react to form a compound. Explain on the basis of electronic concept :

(i) oxidation

(ii) reduction

(iii) oxidising agent

(iv) reducing agent.

Answer

The electronic configuration of:

Potassium (19) = 2, 8, 8, 1

Chlorine (17) = 2, 8, 7

The reaction is :

2K + Cl2 ⟶ K+ + 2Cl-

(i) Oxidation : 2K ⟶ K+
    Potassium undergoes oxidation reaction as it loses an electron.

(ii) Reduction : Cl2 ⟶ 2Cl-
     Chlorine undergoes reduction reaction as it gains an electron.

(iii) Chlorine acts as an oxidising agent and gets reduced.

(iv) Potassium acts as a reducing agent and gets oxidised.

Intext Questions 2

Question 1

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

Answer

The necessary conditions for the formation of covalent molecules are:

  1. Both atoms should have four or more electrons in their outermost shells, i.e., non-metals (exceptions are H, Be, B, Al, etc).
  2. Both the atoms should have high electronegativity.
  3. Both the atoms should have high electron affinity.
  4. Both the atoms should have high ionization energy.
  5. The electronegativity difference between the combining atoms should either be zero or negligible.

Question 2

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

(a) State which one is : (i) a non-metal (ii) metal (iii) chemically inert ?

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

Answer

The electronic configuration of :

A (17) = 2, 8, 7

B (19) = 2, 8, 8, 1

C (10) = 2, 8

(a) (i) A is a non-metal because there are 7 valence electrons in A.

(a) (ii) B is a metal because there is only 1 valence electron in B.

(a) (iii) C is chemically inert element because there are 8 valence electrons in C.

(b) The formula of the compound formed by two of the above elements is BA. The reason being, B loses an electron and A gains that electron to form an ionic bond.

Question 3

Draw electron dot diagram and structure of :

(a) nitrogen molecule

(b) magnesium chloride

(c) methane

Answer

(a) Electron dot diagram and structure of Nitrogen molecule is shown below:

Draw the electron dot structure of Nitrogen molecule. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

(b) Electron dot diagram and structure of magnesium chloride is shown below:

Draw an electron dot diagram to show the formation of Magnesium chloride. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

(c) Electron dot diagram and structure of methane is shown below:

Draw an electron dot diagram to show the formation of Methane. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

Question 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 ?

Answer

(a) Difference between ionic compounds and polar covalent compounds:

Ionic CompoundsPolar Covalent Compounds
The chemical compounds formed as a result of the transfer of electrons from one atom of an element to one atom of another element are called ionic compounds.The compounds formed by mutual sharing of electrons between combining atoms in which the shared pair of electrons are not at equal distance between the two atoms are called polar covalent compounds.

(b) Difference between ionic compounds and covalent compounds:

Ionic CompoundsCovalent Compounds
The chemical compounds formed as a result of the transfer of electrons from one atom of an element to one atom of another element are called ionic compounds.The compounds formed by mutual sharing of one or more pair of electrons between combining atoms are called Covalent Compounds
They are made up of ions and are hard solids.They are made up of molecules and are gases or liquids or soft solids.
They have high melting and boiling point.They have low melting and boiling points.
They are soluble in water but insoluble in organic solvents.They are insoluble in water but dissolve in organic solvents.

(c) Difference between a polar covalent compound and a non-polar covalent compound

Polar Covalent
Compound
Non-Polar Covalent
Compound
The covalent compounds are said to be polar when the shared pair of electrons are not at equal distance between the two atoms.Covalent compounds are non-polar when the shared pair of electron(s) are equally distributed between the two atoms.
They have fractional positive and negative charges on them.No charge separation takes place.
They ionise in water.They don't ionise in water.

Question 5

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

Answer

The given properties of the solid indicates that the solid is an ionic compound consisting of oppositely charged ions held tightly together by strong electrostatic forces of attraction of an ionic bond.

Question 6

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

Answer

A molecule that has both, slight positive and slight negative charge is called a dipole molecule.

For example - In hydrogen chloride, the strong nuclear charge of the chlorine atom (the electro-negativity of chlorine is 3) attracts the shared electron pair towards itself due to which a slight negative charge develops on the chlorine atom. The hydrogen atom (electronegativity 2.1) develops a slight positive charge. Therefore, a polar covalent bond is formed.

What do you understand by dipole (polar) molecule ? Explain it by taking hydrogen chloride as an example. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

Question 7(a)

Explain the bonding in methane molecule using electron dot structure.

Answer

The valency of hydrogen element is 1 and that of carbon is 4. Hydrogen needs one electron to attain stable duplet structure of nearest noble gas - He [2] and carbon needs four electrons to attain stable octet structure of nearest noble gas - Ne [2,8]

One carbon atom shares four electron pairs one with each of the four atoms of hydrogen such that hydrogen acquires a duplet configuration and carbon an octet configuration resulting in the formation of four single covalent bonds.

Electron Dot Structure:

Explain with the help of electron dot diagram the formation of Methane molecule, stating the valency of each element involved. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

Question 7(b)

Methane molecule is non-polar molecule. Explain.

Answer

The bond formed between dissimilar atoms can be non-polar if their electronegativity difference is little and their structure permits the shared pair of electrons to attract equally the linked atoms and thus the molecule becomes symmetrical.
The shared electron pairs in Methane are at an equal distance from the Carbon and the Hydrogen atoms because the two have nearly equal electronegativities (carbon = 2.5, hydrogen = 2.1).

Question 8

Give the characteristic properties of :

(a) electrovalent compounds,

(b) covalent compounds.

Answer

(a) The characteristic properties of electrovalent compounds are:

  1. They are hard solids consisting of ions.
  2. They are non-volatile with high melting and boiling points.
  3. They do not conduct electricity in solid state but are good conductors of electricity in the fused or in aqueous state.
  4. They are good conductors of heat.
  5. They are soluble in water but insoluble in organic solvents.
  6. They show rapid speed of chemical reactions in aqueous solutions.

(b) The characteristic properties of covalent compounds are:

  1. Their constituent particles are molecules. They are gases or liquids or soft solids.
  2. They are volatile with low melting and boiling points.
  3. They are non-conductors of electricity in solid, molten or aqueous state.
  4. They are poor conductors of heat.
  5. They are insoluble in water but dissolve in organic solvents.
  6. They show slow speed of chemical reactions in aqueous solutions.

Question 9(a)

State the type of bond formed, when the combining atoms have :

(i) zero E.N. difference

(ii) small E.N. difference

(iii) large E.N. difference

Answer

(i) Non-polar covalent bond.

(ii) Polar covalent bond.

(iii) Ionic or Electrovalent bond.

Question 9(b)

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

(i) water

(ii) calcium oxide

Answer

(i) In water covalent bond is formed.

Explain with the help of electron dot diagram the formation of Water molecule, stating the valency of each element involved. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

(ii) In calcium oxide ionic bond is formed.

Draw the electron dot structure of Calcium oxide. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

Question 10(a)

Explain the following :

Electrovalent compounds conduct electricity.

Answer

Electrovalent compounds consists of ions but the strong electrostatic force keeps ions in fixed position in the solid state. The force is weakened in the molten state and disappears in aqueous solution state, hence free ions formed help in the conduction of electricity.

Question 10(b)

Explain the following :

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

Answer

Electrovalent compounds have a high melting point and boiling point because there exists a strong force of attraction between the oppositely charged ions, so a large amount of energy is required to break the strong bonding force between ions. While covalent compounds have low melting and boiling points because they have weak forces of attraction between the binding molecules, thus less energy is required to break the force of bonding.

Question 10(c)

Explain the following :

Electrovalent compounds dissolve in water whereas covalent compounds do not.

Answer

Electrovalent compounds dissolve in water because water is a polar compound, it decreases the electrostatic forces of attraction, resulting in free ions in aqueous solution. Hence they dissolve. Whereas covalent compounds do not dissolve in water because covalent compounds are made up of molecules, they do not ionize in water and hence do not dissolve.

Question 10(d)

Explain the following :

Electrovalent compounds are usually hard crystals.

Answer

Electrovalent compounds are usually hard crystals because they have strong electrostatic forces of attraction between their ions, which cannot be separated easily.

Question 10(e)

Explain the following :

Polar covalent compounds conduct electricity.

Answer

Polar covalent compounds have fractional positive and negative charges on them. In aqueous solution state, they undergo ionisation converting the fractional charges to complete charges and ions are produced. These ions helps in the conduction of electricity.

Question 10(f)

Explain the following :

Water is a polar covalent molecule?

Answer

Water is a polar covalent molecule because the shared pair of electrons between hydrogen and oxygen are not at equal distance. There is a slight difference in electronegativities of Oxygen (3.5) and Hydrogen (2.1) due to which the shared pair of electrons is shifted towards Oxygen creating a slight negative charge on it while a slight positive charge is developed on the two Hydrogen atoms making Water a polar covalent molecule.

Question 11

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

Answer

The electronic configuration of :

X (6) = 2, 4

Y (9) = 2, 7

Z (12) = 2, 8, 2

(a) Y forms an anion as it needs just one more electron to complete its octet.

(b) Z forms a cation. It will lose its 2 electrons to achieve a stable electronic configuration thus forming a cation.

(c) Ionic bond is formed between Y and Z and its molecular formula is ZY2.

Question 12

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

Answer

Electrovalent Compound (MgCl2)Covalent Compound (CCl4)
MgCl2 is formed by transfer of electrons from Magnesium to Chlorine so it consists of ionic bonds.CCl4 is formed by sharing of electrons between Carbon and Chlorine so it is made up of covalent bonds.
MgCl2 consists of ions Mg2+ & Cl-.CCl4 consists of molecules — 1 Carbon and 4 Chlorine atoms form a molecule of CCl4.
MgCl2 has higher melting and boiling point.CCl4 has lower melting and boiling point.
An aqueous solution of MgCl2 functions as an electrolyte and conducts electricity.CCl4 does not conduct electricity in solid, liquid or molten state.
MgCl2 is easily soluble in water but insoluble in organic solvents.CCl4 is insoluble in water but soluble in organic solvents.

Question 13

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

Answer

Potassium chloride being an electrovalent compound consists of ions. In aqueous solution state, the electrostatic forces between them weaken and the ions become mobile conducting electricity.
On the other hand, hydrogen chloride is a polar covalent compound. The shared electron pair is shifted towards Chlorine thereby developing a slight negative charge on it and a slight positive charge on hydrogen atom. In its aqueous solution state, hydrogen chloride ionises into Hydronium and Chloride ions as shown in the equation below. These ions help in conducting electricity.
HCl + H2O ⇌ H3O+ + Cl-

Question 14(a)

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

Answer

Electron dot structure of methane:

Draw the electron dot structure of covalent compound methane. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

Electron dot structure of HCl:

Draw the electron dot structure of covalent compound HCl. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10
Methane (CH4)Hydrogen Chloride (HCl)
No charge separation takes place.Charge separation takes place.
The molecule is symmetrical and electrically neutral.There is fractional positive and fractional negative charge on them.

Question 14(b)

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

Answer

Hydrogen Chloride (HCl) & Ammonia (NH3).

Question 14(c)

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

Answer

Hydrogen chloride (HCl)
HCl + H2O ⇌ H3O+ + Cl-

Ammonia (NH3)
NH3 + H2O ⇌ NH4+ + OH-

Question 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.

Answer

With Chlorine — MCl2
With Sulphur — MS

Explanation:
Given, M reacts with oxygen to form an ionic bond MO. Oxygen needs 2 electrons to complete its octet forming the anion O2-. As the compound formed is MO, it means that M has 2 electrons in its valence shell which it donates to Oxygen to attain a stable electronic configuration forming a cation M2+.
Each Chlorine atom accepts 1 electron to complete its octet so 2 Chlorine atoms combine with 1 atom of M to form MCl2. Each Sulphur atom accepts 2 electrons to complete its Octet so 1 Sulphur atom combines with 1 atom of M to form MS.

Question 16

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, the element A will be obtained at the ............. and B at the ............ of the electrolytic cell.

Answer

A has two electrons in M shell i.e., A has valency 2 (metal), and the electronic configuration of B(7) is 2, 5 i.e., B has valency 3 (non-metal).

(a) A ⟶ A2+ + 2e-
     B + 3e- ⟶ B3-

(b) 3A + B2 ⟶ A3B2

(c) Element A will be obtained at the Cathode and B at the Anode of the electrolytic cell.
Reason — As A is a cation, so it is attracted towards cathode as cathode is negatively charged. B is an anion so it is attracted towards anode as anode is positively charged.

Exercise 2

Question 1

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

Answer

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.

Conditions for the formation of coordinate bond are:

(i) One of the two atoms must have at least one lone pair of electrons, e.g., ammonia (NH3), water (H2O).

(ii) Another atom should be short of at least a pair of electrons, e.g., Hydrogen ion (H+).

Question 2

What do you understand by lone pair of electrons.

Answer

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

Question 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

Answer

(a) Polar Covalent Bond,

(b) Ionic Bond,

(c) Polar Covalent Bond,

(d) Non Polar Covalent Bond,

(e) Coordinate & Covalent Bond,

(f) Ionic, Covalent and Co-ordinate Bond.

Question 4(a)

Draw an electron dot diagram for the formation of each of the following :

(i) Hydronium ion,

(ii) Ammonium ion,

(iii) Hydroxyl ion.

State the type of bonding present in them.

Answer

(i) Hydronium ion

Draw an electron dot diagram for the formation of hydronium ion. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

Co-ordinate & Covalent Bond.

(ii) Ammonium ion

Draw the electron dot structure of ammonium ion. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

Co-ordinate & Covalent Bond.

(iii) Hydroxyl ion

Draw the electron dot structure of Hydroxyl ion. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

Polar Covalent Bond.

Question 4(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.

Answer

(i) Ammonium ion (NH4+) & Hydronium ion (H3O+),

(ii) Phosphorus pentoxide (P2O5) & Silicon dioxide or Silica (SiO2),

(iii) Hydrogen sulphide (H2S) & Ammonia (NH3),

(iv) Hydrogen (H2) & Oxygen (O2),

(v) Toluene & Gasoline.

Question 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

Answer

Magnesium (Mg).

Reason — Since, element M forms a chloride with the formula MCl2 which is a solid with high melting point. So, M belongs to the group 2 because it has valency 2.

Question 6

Complete the following

SodiumPhosphorusCarbon
Formula of chloride
Nature of bonding
Physical state of chloride

Answer

SodiumPhosphorusCarbon
Formula of chlorideNaClPCl3, PCl5CCl4
Nature of bondingIonic BondCovalent BondCovalent Bond
Physical state of chlorideSolidLiquid, SolidLiquid

Question 7(a)

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

Answer

Calcium oxide (CaO) is formed by one calcium and one oxygen atom.

Chlorine (Cl2) molecule is formed by two chlorine atoms.

Water (H2O) is formed by two hydrogen and one oxygen atom.

Carbon Tetrachloride(CCl4) is formed by one carbon and four chlorine atoms.

Question 7(b)

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

Answer

In Calcium oxide (CaO), Calcium needs to lose 2 electrons and Oxygen gains that 2 electrons to attain the nearest noble gas configuration.

In Chlorine (Cl2) molecule, each Chlorine atom needs an electron to complete its octet. So, two Chlorine atoms share a pair of electrons to attain the nearest noble gas configuration.

In Water (H2O), each Hydrogen atom needs one electron and one Oxygen atom needs two electrons to complete their duplet and octet respectively. So, each Hydrogen shares a pair of electrons with Oxygen to attain the nearest noble gas configuration.

In Carbon Tetrachloride (CCl4), each Carbon atom needs 4 electrons and each Chlorine atom needs one electron to complete their octet. So, each Chlorine shares a pair of electrons with Carbon to attain the nearest noble gas configuration.

Question 8

Complete the following :

(a) When the nuclei of two different 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) Ionic or electrovalent compounds do not conduct electricity in their ............... state (fused/solid).

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

Answer

(a) Unequal, Polar

(b) Middle, Equally

(c) Solid

(d) Electrovalent, Electrostatic

Question 9

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.

Answer

(i) C → covalent
Reason : Since, X consists of molecules. Therefore, covalent bond is present.

(ii) C → Low melting point and low boiling point.
Reason : Covalent compounds have low melting and boiling points.

(iii) D → not conduct electricity.
Reason : Covalent compounds are non-conductor of electricity in solid, molten or aqueous state.

Question 10(a)

Electrons are getting added to an element Y :

(i) is Y getting oxidized or reduced ?

(ii) which electrode will Y migrate to during the process of electrolysis ?

Answer

(i) Y is getting reduced as reduction is gain of electrons.

(ii) Y migrates towards anode. Y is negatively charged as electrons are added to it. So, it migrates towards the positive terminal that is anode.

Question 10(b)

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

Answer

When acids dissolve in water they produce hydronium ion. Structure of hydronium ion is shown below:

Draw an electron dot diagram for the formation of hydronium ion. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

Question 10(c)

Explain why Carbon tetrachloride does not dissolve in water.

Answer

Carbon tetrachloride is a non-polar compound and water is a polar compound. Same kind of compounds dissolve in each other that's why carbon tetrachloride does not dissolve in water.

Question 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 ?

Answer

QS exist in hard solid state.
Reason — As QS is an ionic compound, it consists of ions bond tightly together by strong electrostatic forces between them. Due to this it is a hard solid.

Question 11(b)

Elements Q and S react together to form an ionic compound. Can Q and S, both be metals ? Justify your answer.

Answer

No, Q and S both can't be metals because Q and S react together to form an ionic compound. It is only possible when one of them is metal and the other one is non-metal.

Question 11(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 a liquid.

Answer

B → it has a high melting point.
Reason — There exists a strong force of attraction between the oppositely charged ions, so a large amount of energy is required to break the strong bonding force between ions.

Question 11(d)

When a metal atom becomes an ion :

    A.  it loses electrons and is oxidized,
    B.  it gains electrons and is reduced,
    C.  it gains electrons and is oxidized,
    D.  it loses electrons and is reduced.

Answer

A → it loses electrons and is oxidized.
Reason — Metals have the tendency to lose electrons and get oxidised to attain a stable electronic configuration.

Question 12(a)

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

Answer

Magnesium is oxidized and Chlorine is reduced.

In the formation of magnesium chloride the reaction is :

Mg + Cl2 ⟶ Mg+2 + 2Cl-

Oxidation : Mg ⟶ Mg+2

Reduction : Cl2 ⟶ 2Cl-

Question 12(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.

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

Answer

(i) Covalent Bond.

(ii) Co-ordinate Bond.

Question 1a(2009)

The one which is composed of all the three kinds of bond [ionic, covalent and coordinate bond] is:

  1. Sodium chloride
  2. Ammonia
  3. Carbon tetrachloride
  4. Ammonium chloride

Answer

Ammonium chloride
Reason — When ammonium chloride NH4Cl is formed cation NH4+ (having 3 covalent and one coordinate bond) and anion Cl- are attracted towards each other, due to electrical charge existing between them ionic bond is formed. Thus, ammonium chloride is a good example of compound having all three types of bonds i.e., covalent, coordinate and ionic bond.

Question 1b(2009)

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

Answer

Structural formula of carbon tetrachloride is given below:

Draw the structural formula of carbon tetrachloride and state the type of bond present in it. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

Covalent bond is present in carbon tetrachloride.

Question 1a(2010)

Select the correct answer from A, B, C and D — Metals lose electrons during ionization — this change is called:

  1. Oxidation
  2. Reduction
  3. Redox
  4. Displacement

Answer

Oxidation
Reason — Oxidation is the process when an atom or ion loses electrons in order to attain a stable state.

Question 1b(2010)

Select the right answer from the choices — covalent bond / ionic bond / covalent & coordinate bond for each of the following —

(i) Sodium chloride

(ii) Ammonium ion

(iii) Carbon tetrachloride

Answer

(i) Sodium chloride — Ionic bond

(ii) Ammonium ion — Covalent and coordinate bond

(iii) Carbon tetrachloride — Covalent bond

Question 1a(2011)

(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]

Answer

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

(ii) Electrovalent compounds have a high boiling point.

(iii) A molecule of nitrogen contains a triple bond.

Question 1b(2011)

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

Electron dot diagram showing the lone pair effect for formation of NH41+ ion from NH3 gas and H1+ is given below:

By drawing an electron dot diagram, show the lone pair effect leading to the formation of ammonium ion from ammonia gas and hydrogen ion. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

Question 1c(2011)

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

Answer

In hydrogen chloride, the strong nuclear charge of the chlorine atom attracts the shared electron pair towards itself, i.e., negative charge shifts towards the chlorine atom thereby developing a slight negative charge on it. The hydrogen atom develops a slight positive charge. Therefore, a polar covalent bond is formed as shown below :

Give reasons - Hydrogen chloride can be termed as a polar covalent compound. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

Question 1a(2012)

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

Answer

Electron dot diagram showing the structure of Hydronium ion is given below:

Draw an electron dot diagram of the structure of hydronium ion. State the type of bonding present in it. Chemical Bonding, Concise Chemistry Solutions ICSE Class 10

Co-ordinate bond is present in hydronium ion.

Question 1b(2012)

There are three elements E, F, G with atomic numbers 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.

Answer

EG is the chemical formula.
The electronic configuration of E is (2,8,8,1) and G is (2,8,7). We observe that E tends to donate one electron and G tends to gain one electron to attain a stable state. Hence, the the two oppositely charged ions attract each other to form an ionic compound EG.
Ionic bond will be formed.

Question 1a(2013)

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

Answer

Coordinate bond

Question 1b(2013)

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

  1. Ammonia
  2. Ammonium chloride
  3. Sodium hydroxide
  4. Calcium chloride

Answer

Ammonium chloride

Question 1c(2013)

State which is not a typical property of an ionic compound?

  1. High melting point.
  2. Conducts electricity in molten and in the aqueous solution state.
  3. Are insoluble in water.
  4. Exist as oppositely charged ions even in the solid state.

Answer

Are insoluble in water
Reason — Ionic compounds are soluble in water. They are insoluble in organic solvents. Water [polar solvent] has a high dielectric constant i.e. capacity to weaken the force of attraction, thus resulting in free ions.
Organic solvents [non-polar] have low dielectric constants and do not cause dissolution.

Question 1d(2013)

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

Answer

 Carbon tetrachlorideSodium chloride
Solubility in waterInsoluble in waterSoluble in water
Electrical conductivityNon ConductorGood conductors in aqueous state or molten state

Question 1a(2014)

Compound 'X' consists of only molecules. 'X' will have —

  1. A Crystalline hard structure
  2. A low melting and boiling point
  3. An ionic bond
  4. A strong force of attraction between it's molecules.

Answer

A low melting and boiling point
Reason — There are weak Vander Waals forces of attraction between molecules. Thus, less amount of energy is required to break these forces of attraction.

Question 1b(2014)

The molecule which contains a triple covalent bond is:

  1. ammonia
  2. methane
  3. water
  4. nitrogen

Answer

nitrogen
Reason — The valency of nitrogen element is 3. Nitrogen needs three electrons to attain stable octet structure of nearest noble gas - Ne [2,8].
Each of the two N atoms contributes three electron so as to have three shared pair of electrons between them. Both atoms attain stable – octet structure, resulting in the – formation of a – triple covalent bond [N≡N] between them

Question 1c(2014)

Give word/phrase for : Formation of ions from molecules.

Answer

Ionisation

Question 1d(2014)

Give a reason why covalent compounds exist as gases, liquids or soft solids?

Answer

Covalent compounds exist as gases, liquids or soft solids as they have weak force of attraction between their molecules.

Question 1a(2016)

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

ElementWXYZ
Electronic
Configurations
2, 8, 12, 8, 72, 51

Answer the following questions based on the table above:

(i) What type of bond is formed between:

  1. W and X
  2. Y and Z

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

  1. X and Z
  2. W and X

Answer

(i) Type of bond formed

(a) W (2,8,1) and X (2,8,7) — Electrovalent bond is formed as W donates 1 electron and X takes up that electron and both attain a stable octet.

(b) Y (2, 5) and Z (1) — Covalent bond as electron sharing takes place between the two elements. The valency of Z element is 1 and that of Y is 3. Z needs one electrons to attain stable duplet structure of nearest noble gas - He [2] and Y needs three electrons to attain stable octet structure of nearest noble gas - Ne [2,8]
One Y atom shares three electron pairs one with each of the three atoms of Z such that Z acquires a duplet configuration and Y attain a stable octet configuration resulting in the formation of three single covalent bonds.

(ii) Formula of the compound formed

(a) X (2,8,7) and Z (1) — XZ as X needs one 1 electron to complete it's octet and Z needs needs one electron to complete it's duplet hence, they both share one electron pair and forms ZX compound.

(b) W (2,8,1) and X (2,8,7) — WX as W has the tendency to donate one electron and gain stability whereas X has the tendency to gain one electron to be stable. Hence, W donates one electron and X takes it and form WX compound.

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