Question 1

Question 1Draw an electron dot diagram of the structure of — hydronium ion. State the type of bonding present in it.

Accepted Answer

Electron dot diagram showing the structure of Hydronium ion is given below:Co-ordinate bond is present in hydronium ion.

Question 2

Question 2Draw the geometrical atomic structure representing the electronic configuration of atoms of elements of :Period-2group 14 [IVA] — carbon [at no. 6]group 15 [VA] — nitrogen [at. no. 7]group 16 [VI A] — oxygen [at no. 8]Period-3group 1[IA] — sodium [at no. 11]group 2[IIA] — magnesium [at. no. 12]group 17[VIIA]— chlorine [at. no. 17]Period-4group 2[IIA] — calcium [at. no. 20].

Accepted Answer

Period-2(i) Group 14 [IV A] — Carbon[at no. 6](ii) Group 15 [VA] — Nitrogen [at. no. 7](iii) Group 16 [VI A] — Oxygen [at no. 8]Period-3(i) Group 1[IA] — Sodium [at no. 11](ii) Group 2[IIA] — Magnesium [at. no. 12](iii) Group 17[VIIA] — Chlorine [at. no. 17]Period-4(i) group 2[IIA] — Calcium [at. no. 20].

Question 3

Question 12Explain with the help of :(i) an ionic equation(ii) electron dot structural diagramthe formation of the following :(a) Sodium chloride(b) Calcium oxide(c) Magnesium chloride.(at. nos. Na = 11, Cl = 17, Ca = 20, O = 8, Mg = 12)

Accepted Answer

(a) Sodium Chloride :Ionic equationNa - 1e- ⟶ Na1+ [oxidation][atom]      [cation][2,8,1]       [2,8]Cl + 1e- ⟶ Cl1- [reduction][atom]      [anion][2,8,7]       [2,8,8]Na + Cl ⟶ Na1+ Cl1- ⟶ NaClElectron dot structural diagram(b) Calcium OxideIonic EquationCa - 2e- ⟶ Ca2+ [oxidation][atom]      [cation][2,8,8,2]     [2,8,8]O + 2e- ⟶ O2- [reduction][atom]      [anion][2,6]          [2,8]Ca + O ⟶ Ca2+O2- ⟶ CaOElectron dot structural diagram(c) Magnesium chloride.Ionic EquationMg - 2e- ⟶ Mg2+ [oxidation][atom]      [cation][2,8,2]       [2,8]2Cl + 2e- ⟶ 2Cl- [reduction][atom]      [anion][2,8,7]       [2,8,8]Mg + 2Cl ⟶ Mg2+2Cl- ⟶ MgCl2Electron dot structural diagram

Question 4

Question 14Define or explain the terms:(i) Covalent or molecular bond(ii) Covalent or molecular compound(iii) Covalency(iv) Shared pair of electrons.

Accepted Answer

(i) Covalent or molecular 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.Depending on the number of electron pairs shared : bond is single [-], double [=], or triple [≡] covalent.(ii) Covalent or molecular compound — The chemical compound formed due to the mutual sharing of electrons between the given pair of atoms thereby forming a covalent bond is called covalent compound.(iii) Covalency — Covalency of an atom is the number of electron pairs which the atom shares with one or more atoms of the same or different kind to achieve stable electronic configuration. For example : the covalency of hydrogen is 1, oxygen is 2 and nitrogen is 3.(iv) Shared pair of electrons — A pair of electrons which is being shared between two atoms resulting in the formation of a covalent bond is called a shared pair of electrons.

Question 5

Question 15Give two differences between the covalent compounds – methane (non-polar) and HCl (polar)

Accepted Answer

Methane (non-polar)covalent compoundHCl (polar)covalent compoundCovalent compounds are said to be non-polar when shared pair of electrons are equally distributed between the two atoms.Covalent compounds are said to be polar when shared pair of electrons are unequally distributed between the two atoms.The covalent molecule is symmetrical and electrically neutral.The atom which attracts electrons more strongly develops a slight negative charge while the other develops a slight positive charge.

Question 6

Question 16Explain with the help of electron dot diagrams the formation of the following molecules, stating the valency of each element involved.(a) Hydrogen(b) Chlorine(c) Oxygen(d) Nitrogen(e) Water(f) Methane(g) Carbon tetrachloride(h) Ammonia(i) Carbon dioxide[at. nos. H = 1, C = 6, N = 7, O = 8, Cl = 17]

Accepted Answer

(a) Formation of Hydrogen molecule (H2) — The valency of hydrogen element is 1. It needs one electron to attain stable duplet structure of nearest noble gas - He [2].Each of the 'H' atoms contribute one electron so as to have one shared pair of electrons between them. Both atoms attain stable duplet structure resulting in the formation of a single covalent bond [H-H] between them.Electron Dot Structure:(b) Formation of Chlorine (Cl2) — The valency of chlorine element is 1. It needs one electron to attain stable octet structure of nearest noble gas - Ar [2, 8, 8].Each of the 'Cl' atoms contribute one electron so as to have one shared pair of electrons between them. Both atoms attain stable octet structure resulting in the formation of a single covalent bond [Cl-Cl] between them.Electron Dot Structure:(c) Formation of Oxygen molecule (O2) — The valency of oxygen element is 2. It needs two electrons to attain stable octet structure of nearest noble gas - Ne [2,8].Each of the two 'O' atoms contribute two electrons so as to have two shared pair of electrons between them. Both atoms attain stable octet structure resulting in the formation of a double covalent bond [O=O] between them.Electron Dot Structure:(d) Formation of Nitrogen Molecule (N2) — 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.Electron Dot Structure:(e) Formation of Water Molecule (H2O) — The valency of hydrogen element is 1 and that of oxygen is 2. Hydrogen needs one electrons to attain stable duplet structure of nearest noble gas - He [2] and oxygen needs two electrons to attain stable octet structure of nearest noble gas - Ne [2,8]Each of the two hydrogen atoms shares an electron pair with the oxygen atom such that hydrogen acquires a duplet configuration and oxygen an octet configuration resulting in the formation of two single covalent bonds [H-O-H] in the molecule of water.Electron Dot Structure:(f) Formation of Methane Molecule (CH4) — 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:(g) Formation of Carbon tetrachloride Molecule (CCl4) — The valency of carbon element is 4 and that of chlorine is 1. Chlorine needs one electron to attain stable octet structure of nearest noble gas - Ar [2,8,8] 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 chlorine such that chlorine and carbon attain a stable octet configuration resulting in the formation of four single covalent bonds.Electron Dot Structure:(h) Formation of Ammonia Molecule (NH3) — The valency of hydrogen element is 1 and that of nitrogen is 3. Hydrogen needs one electrons to attain stable duplet structure of nearest noble gas - He [2] and nitrogen needs three electrons to attain stable octet structure of nearest noble gas - Ne [2,8]One nitrogen atom shares three electron pairs one with each of the three atoms of hydrogen such that hydrogen acquires a duplet configuration and carbon attain a stable octet configuration resulting in the formation of three single covalent bonds .Electron Dot Structure:(i) Formation of Carbon dioxide Molecule (CO2) — The valency of carbon element is 4 and that of oxygen is 2. Carbon needs four electrons to attain stable octet structure of nearest noble gas - Ne [2,8] and oxygen needs two electrons to attain stable octet structure of nearest noble gas - Ne [2,8]One carbon atom shares two electron pairs one with each of the two atoms of oxygen such that oxygen and carbon attain a stable octet configuration resulting in the formation of two double covalent bonds.Electron Dot Structure:

Question 7

Question 17.1Give reasons for the following:Molecules of hydrogen and chlorine have single covalent bonds between their atoms while oxygen has a double covalent and nitrogen a triple covalent bond respectively.

Accepted Answer

Depending on the number of electron pairs shared, covalent bond is single [-], double [=], or triple [≡] covalent.Hydrogen — Each of the 'H' atoms contribute one electron so as to have one shared pair of electrons between them. Both atoms attain stable duplet structure resulting in the formation of a single covalent bond [H-H] between them.Chlorine — Each of the two Cl atoms contributes one electron so as to have one shared pair of electrons between them. Both atoms attain stable octet structure, resulting in the formation of a single covalent bond [Cl–Cl] between them.Oxygen — Each of the two O atoms contributes two electron so as to have two shared pair of electrons between them. Both atoms attain stable octet structure, resulting in the formation of a double covalent bond [O=O] between them.Nitrogen — 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 8

Question 17.3Give reasons for the following:Formation of ammonia involves one atom of nitrogen sharing three electron pairs one with each of the three atoms of hydrogen.

Accepted Answer

The valency of nitrogen is 3 and that of hydrogen is 1. N needs three electrons to attain a stable octet and H needs one electron to attain stable duplet. Hence, one atom of nitrogen shares three electron pairs one with each of the three atoms of hydrogen.Electron Dot Structure:

Question 9

Question 18Explain the terms :(a) Lone pair of electrons(b) Coordinate bondExplain diagrammatically the lone pair effect of:(a) The nitrogen atom of the ammonia molecule leading to the formation of ammonium ions [NH4]+(b) The oxygen atom of the H2O molecule leading to formation of hydronium [H3O]+ and hydroxyl ions [OH]-

Accepted Answer

(a) Lone pair of electrons — They are a pair of electrons not shared with any other atom.(b) Coordinate Bond — It is a type of covalency which involves one of the combining atoms contributing both of the shared electrons. i.e., a bond formed by a shared pair of electrons with both electrons coming from the same atom.(a) Formation of ammonium ions [NH4]+In ammonia, the 'N' atom contains one lone pair of electrons after completing it's octet. This lone pair is accepted by the hydrogen ion of water leading to the formation of a coordinate covalent bond:−N∣∣→H-\overset{|}{\underset{|}{	ext{N}}} arr 	ext{H}−∣N​∣​→H(b) Formation of hydronium (H3O)+ and hydroxyl ions [OH]-In water, the 'O' atom contains two lone pairs of electrons after completing it's octet. These lone pairs are accepted by the hydrogen ion leading to the formation of coordinate covalent bond:−O∣→H-\overset{|}{	ext{O}}arr	ext{H}−O∣→H

Question 10

Question 19Give reasons for the following:Electrovalent compounds are soluble in water, insoluble in organic solvents, good conductors of electricity in molten or aq. solution state, have high melting points and undergo electrolytic dissociation on passage of electric current, while covalent compounds are soluble in organic solvents, insoluble in water, non-conductors of electricity, have low melting points and undergo ionization on passage of electric current.AnswerElectrovalent compoundsSolubility — Soluble in water, Insoluble in organic solvents.Reason — 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.Conduction of Electricity — Good conductors of electricity in molten or aqueous solution state and in solid state, they are non-conductors.Reason — 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 migrate to oppositely charged electrodes.Melting Point — High melting point.Reason — Strong electrostatic force of attraction between ions. Large amount of energy required to break the force of attraction.Dissociation — Undergoes electrolytic dissociation on passage of electric current.Reason — Process involves separation of ions already present in the ionic compound.E.g. NaCl ⇌ Na1+ + Cl1- [in molten state]Covalent compoundsSolubility — Soluble in organic solvents [non-polar] but insoluble in water [polar].Reason — Organic solvents [non-polar] e.g., the benzene, alcohol, dissolves non-polar covalent compounds [like dissolves like]. Water [polar solvent] cannot dissolve non-polar compounds, but dissolves polar.Conduction of Electricity — Non-conductors of electricity.Reason — Non-polar compounds e.g., CCl4 contain molecules and not free ions. Hence, are non conductors. Polar covalent compounds e.g., HCl, NH3 show charge seperation and dissociate in H2O.Melting Point —Low melting points.Reason — Weak Vander Waals force of attraction between molecules. Thus, less amount of energy is required to break these forces of attraction.Ionization — Undergoes ionization in solution state on passage of electric current. Process involves formation of ions from molecules which are not in ionic state.E.g. HCl ⟶ H1+ + Cl1- [in solution state]

Accepted Answer

Answer: Solubility, Conduction of Electricity, Melting Point, Dissociation, Solubility, Conduction of Electricity, Melting Point, Ionization

Question 11

Question 4Acids dissolve in water and produce positively charged ions. Draw the structure of these positive ions.

Accepted Answer

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

Question 12

Question 6Draw the structural formula of carbon tetrachloride and state the type of bond present in it.

Accepted Answer

Structural formula of carbon tetrachloride is given below:Covalent bond is present in carbon tetrachloride.

Question 13

Question 11The following table shows the electronic configuration of the elements W, X, Y, Z :ElementWXYZElectronicConfigurations2, 8, 12, 8, 72, 51Answer the following questions based on the table above:(i) What type of bond is formed between:W and XY and Z(ii) What is the formula of the compound formed between :X and ZW and X

Accepted 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.

Question 14

Question 5A compound is formed between atoms A and B. The electronic configuration of A is 2,8,1 and B is 2,6.(a) Write the equation of the formation of ions of A and B.(b) Why do A and B form ions?(c) Which of the following can form a compound?    (i) A and A (ii) A and B (iii) B and B    Also state the type of bonding present in the compound(d) If A and B combines, which of them will get oxidised?(e) Draw an electron dot diagram of the ionic compound formed in part (c).(f) Write the formula of the compound formed in part (c) which has a    (i) high melting and boiling point    (ii) gaseous compound    (iii) good conductor of electricity in molten state.

Accepted Answer

(a) Atom A loses one electron:A ⟶ A+ + e-Atom B gains two electronsB + 2e- ⟶ B2-(b) A and B form ions to achieve a stable noble gas configuration:A loses 1 electron → becomes A⁺ with a configuration of 2,8 (like neon).B gains 2 electrons → becomes B²⁻ with a configuration of 2,8 (also like neon).(c) A and B can form a compound, electrovalent bonding will be present in it.(d) Oxidation is the loss of electrons.A (sodium) loses 1 electron to form Na+. Hence A gets oxidised(e) Electron dot diagram is shown below:(f)(i) A2B(As A2B is an ionic compound, hence, it will have high melting and boiling point)(ii) A and B will not form a gaseous compound.(iii) A2B(As A2B is an ionic compound, hence, ions will be free to move when in molten state)

Question 15

Question 9Explain with the help of ionic equation and electron dot structural diagram the formation of the following electrovalent compounds.(a) NaCl(b) MgCl2(c) CaO

Accepted Answer

(a) Na+ + Cl- ⟶ NaClThe electron dot structural diagram is:(b) Mg+2 + 2Cl- ⟶ MgCl2The electron dot structural diagram is:(c) Ca+2 + O-2 ⟶ CaOThe electron dot structural diagram is:

Question 16

Question 10Compare :(a) sodium atom and sodium ion(b) chlorine atom and chloride ionwith respect toatomic structureelectrical statechemical actiontoxicity

Accepted Answer

(a) Comparison between sodium atom and sodium ion:PropertySodium AtomSodium IonAtomic 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 IonAtomic 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 17

Question 3Draw electron dot diagram and structure of :(a) nitrogen molecule(b) magnesium chloride(c) methane

Accepted Answer

(a) Electron dot diagram and structure of Nitrogen molecule is shown below:(b) Electron dot diagram and structure of magnesium chloride is shown below:(c) Electron dot diagram and structure of methane is shown below:

Question 18

Question 4What 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 ?

Accepted Answer

(a) Difference between ionic compounds and polar covalent compounds:Ionic CompoundsPolar Covalent CompoundsThe 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 CompoundsThe 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 CompoundsThey 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 compoundPolar CovalentCompoundNon-Polar CovalentCompoundThe 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 19

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

Accepted 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.

Question 20

Question 9(b)State the type of bond formed, and draw Lewis structure of(i) water(ii) calcium oxide

Accepted Answer

(i) In water covalent bond is formed.(ii) In calcium oxide ionic bond is formed.

Chemical Bonding

2012

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