Chemical Bonding

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

(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.

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.

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

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.

(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.

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:

(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 YX.

(a) Na⁺ + Cl^- ⟶ NaCl

The electron dot structural diagram is:

(b) Mg⁺² + 2Cl^- ⟶ MgCl₂

The electron dot structural diagram is:

(c) Ca⁺² + O^-2 ⟶ CaO

The electron dot structural diagram is:

(a) Comparison between sodium atom and sodium ion:

(b) Comparison between chlorine atom and chloride ion:

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.

(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).

A reaction in which oxidation and reduction occur simultaneously is called an oxidation-reduction reaction or redox reaction. It involves 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.

In the formation of electrovalent compounds, the transfer of electrons is involved. The electropositive atom loses electrons and undergoes oxidation while the electronegative atom gains electrons and undergoes reduction. Hence, formation of electrovalent compound is a redox reaction.

(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

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.

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.

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.

(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:

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

(b) Difference between ionic compounds and covalent compounds:

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

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.

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.

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:

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).

(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.

(i) Non-polar covalent bond.

(ii) Polar covalent bond.

(iii) Ionic or Electrovalent bond.

(i) In water covalent bond is formed.

(ii) In calcium oxide ionic bond is formed.

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.

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.

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.

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

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.

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.

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.

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^-

Electron dot structure of methane:

Electron dot structure of HCl:

Hydrogen Chloride (HCl) & Ammonia (NH₃).

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

Ammonia (NH₃)
NH₃ + H₂O ⇌ NH₄⁺ + OH^-

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 O^2-. 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.

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^- ⟶ B^3-

(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.

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.

(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.

it has a high melting point

Reason — Electrovalent compounds have a high melting 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.

It loses electrons and is oxidized

Reason — Metals readily give the valence electron during reactions and are hence oxidised.

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 and 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.

Insolubility 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.

Oxidation

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

Low melting and low 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.

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.

Both Q and R

Reason — Covalent bond between two atoms is favoured when

1. The electronegativity difference between the combining atoms should either be zero or negligible.
2. Both the atoms should have high electron affinity.
3. Both the atoms should have high electronegativity.

Hence both Q and R are correct.

Both A and R are true and R is the correct explanation of A.

Explanation — The anion is formed easily if the electron affinity value is high. A high (more negative) electron affinity means an atom releases a significant amount of energy when it gains an electron indicating it strongly attracts electrons. This makes it easier for the atom to accept an electron and form a negative ion (anion). Hence the Assertion (A) is true.
Electron affinity encourages electron acceptance, which is a step in ionic bond formation. Hence Reason (R) is also true and it correctly explains Assertion (A).

Both A and R are true and R is the correct explanation of A.

Explanation — By sharing the valence electron pair, atoms can combine to form Covalent bond and by transfering electron(s), atoms establish a strong electrostatic attraction to form an Ionic bond.
Atoms always try to attain their stable elctron configuration i.e., to have 8 electrons in their valence shell. So, both Assertion (A) and Reason (R) are true and Reason (R) correctly explains Assertion (A).

A is true but R is false.

Explanation — Ionic compounds when in molten or aqueous state dissociate into free moving ions, which carry electric current. That is why substances like NaCl conduct electricity when dissolved in water or melted. Hence Assertion (A) is true.
Reason (R) is false because ionic compounds consist of positive and negatively charged ions bound by strong electrostatic forces.

A is true but R is false.

Explanation — The unshared pair of electrons is known as lone pair of electrons. Hence the Assertion (A) is true.
Ammonium molecule has lone pair of electrons NOT ammonium ion. Ammonium ion is formed when the lone pair of electron present on nitrogen atom in ammonium molecule is accepted by hydrogen ion and forms a coordinate bond. So, there are no lone pair of electrons left. Hence Reason (R) is false.

A is false but R is true.

Explanation — Electrovalent compounds cannot disssociate into ions in solid state hence they do not conduct electricity but they are very good conductors of electricity in the molten or in aqueous state. Hence the Assertion (A) is false.

Electrovalent compounds are composed of ions that are held by strong electrostatic force of attraction, which cannot be seperated easily. Hence Reason (R) is true.

(a) Unequal, Polar

(b) Middle, Equally

(c) Solid

(d) Electrovalent, Electrostatic

(e) Sharing

(f) High

(a) Ionisation

(b) Coordinate bond

(c) Covalent Bond

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

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

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

(d) Hydrogen (H₂) & Oxygen (O₂),

(e) Toluene & Gasoline.

(f) Calcium Carbonate (CaCO₃)

(g) Ammonium chloride (NH₄Cl)

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^-

(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.

1. (c) Al

2. The formula X₂O₃ indicates that the element 'X' forms a trivalent oxide. Thus, 'X' has a valency of 3 like that of Al (Valency of Na, Mg and Si are 1, 2 and 4, respectively). In Group 13, the elements typically form oxides with the general formula X₂O₃, where 'X' represents the element. The oxides of Group 13 elements, such as Al₂O₃ (aluminum oxide), have high melting points due to the strong ionic bonds between the metal cations and the oxide anions.

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

(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.

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 :

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

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.

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.

(a) Atom A loses one electron:
A ⟶ A⁺ + e^-
Atom B gains two electrons
B + 2e^- ⟶ B^2-

(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)

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⁺).

(i) Hydronium ion

Co-ordinate & Covalent Bond.

(ii) Ammonium ion

Co-ordinate & Covalent Bond.

(iii) Hydroxyl ion

Polar Covalent Bond.

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.

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.

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

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.

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.

Structural formula of carbon tetrachloride is given below:

Covalent bond is present in carbon tetrachloride.

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

Co-ordinate bond is present in hydronium ion.

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

(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.

(a) A

Reason — G being present in Group 17 is a non-metal; covalent bonds form between non-metals. Element A being a non-metal shares its single electron with G to form the stable molecule AG.

(b) B

Reason — The cathode is the negative electrode, attracting positive ions (cations). Element B is a metal that loses electrons to form a B²⁺ cation.

(c) E

Reason — E is a non metal which belongs to Group 16. Hence has the valency of 2.

(d) F

Reason — Here F is present in Group 18 and all Group 18 elements are inert gases.

(e) I

Reason — Electronegativity decreases down a group. In the second column, I is below B, so I has the lowest electronegativity.

(f) H

Reason — Metallic character increases down a group and decreases from left to right across a period. Since H is towards the bottom left of the given table, it is the most metallic element.

(g) Ionic bond; Formula: IE

Reason — I is a metal of Group 2 and has valency 2. E is a non-metal of Group 16 and also has valency 2. Therefore, electrons are transferred from I to E, forming an ionic compound with the formula IE.

(h) The electron dot (Lewis) diagram for IG₂:

Reason — I belongs to Group 2, so it loses two electrons to form I²⁺. G belongs to Group 17, so each G atom gains one electron to form G^-. Therefore, one atom of I combines with two atoms of G to form IG₂.