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1. The smaller cation and larger anion shows greater covalent character due to greater extent of polarisation.

2. The size of Li⁺ ion is smaller than Na⁺ ion and hence the polarising power of Li⁺ ion is more. So lithium chloride is more covalent than sodium chloride.

Lithium iodide is more covalent than Lithium chloride as the size of I^- ion is larger than Cl^- ion. Hence I^- ion will be more polarised than Cl^- ion by the cation Li⁺ . So LiI is more covalent than LiCl.

(d) The bond order of O₂ is 2 and it is paramagnetic

1. According to molecular orbital theory the atomic orbitals of large number of atoms in a crystal overlap to form numerous bonding and anti-bonding molecular orbitals without any band gap.

2. The bonding molecular orbitals are completely filled with an electron pair in each and the anti-bonding molecular orbitals are empty.

3. Absence of band gap accounts for high electrical conductivity of metals.

4. High thermal conductivity is due to thermal excitation of many electrons from the valence band to the conduction band.

5. With an increase in temperature, the electrical conductivity decreases due to vigorous thermal motion of lattice ions that disrupts the uniform lattice structure. that is required for free motion of electrons within the crystal.

Common Errors

1. The number of bonds formed by elements may go wrong.
2. When writing Lewis structure, electrons may be written in an irregular way.
3. Coordinate covalent bond should not be written as a line

Rectifications

1. Always hydrogen and fluorine form 1 bond Oxygen 2 bonds, Nitrogen 3 bonds, Carbon 4 bonds
2. When writing lewis structure, each atom should be surrounded by eight electrons in such a way as 4 pairs of electrons.
3. Coordinate covalent bond should be written from donor atom to acceptor atom as an arrow mark Donor→ Acceptor

Option : (C) π* 

O₂^2- < O₂^- < O₂ < O₂⁺

A covalent bond formed between the two atoms due to the sideways overlap of their p-orbitals is called a pi (π) bond.

A covalent bond formed due to the overlap of orbitals of the two atoms along the line joining the two nuclei (orbital axis) is called sigma (σ) bond.

In a σ bond the overlapping is along the axis and is maximum extent. Where as π bond overlapping is sidewise and overlapping is minimum.

NH₄⁺>NH₃>NH²

Formation of ions from molecules →Ionisation.

• Oxidation involves the removal of electrons.
• Reduction involves the addition of electrons.
• Oxidation and reduction go side by side.

As they have weak force of attraction between their molecules. 

• The compounds containing molecules that are formed by sharing of electrons are known as covalent compounds.
• Covalent compounds are soft with low melting and boiling points.

Sodium ion has eight electrons in its valency shell and it is the minimum state of energy, while the sodium metal has one electron in valency shell, so the sodium metal is very reactive. 

In covalent compounds, the molecules are held together by weak Van der Waal’s forces. In liquids, the molecules are weakly attracted whereas in gases, these forces are almost non¬existent. Hence, they are generally liquids or gases.

Ammonia (gas) is a covalent compound.

As there are no ions present in it, it does or conduct electricity.Ammonia gas dissolves in water to give an aqueous solution of ammonium hydroxide.

NH₃ (g) + H₂O (l) → NH₄OH (aq)

Ammonium hydroxide is a weak electrolyte which ionises to a small extent to give ammonium ions and hydroxide ions.

Due to the presence of these ions an aqueous solution of NH₃ gas in water conducts electricity. 

The covalent compounds do not have positive or negative ions in their fused state. Thus, when electric potential is supplied, no ions migrate to opposite poles and hence no conduction of electric current takes place.

Phosphorus atom has 5 electrons in its outermost orbit. H – atoms contribute one electron each to make in all 8 electron around P – atom. Thus 4 pairs of electrons would be distributed in a tetrahedral manner around the central atom. Three pairs from three P – H bonds while the fourth pair remains unused. Due to repulsion between the bp and 1p, the shape is not of tetrahedral but trigonal pyramidal molecule.

In NH₃, there is hydrogen bonding whereas in PH₃ there is no hydrogen bonding.

Methane has symmetrical tetrahedral structure hence dipole moment is zero. Therefore it is non polar.

BF₃ is zero dipole moment.

In H₂O, hydrogen is combined with highly electronegative element and also forms intermolecular hydrogen bond. But S is less electronegative and in H₂S there is no hydrogen bonding.

(A) BF₃ is a symmetrical molecule. It has zero dipole moment. Oxygen being more electronegative than S, bond moment of O-H is more than S-H. So the dipole moment are in the order of BF₃<H₂S<H₂O.

(B) The anion size in increasing order is Cl^-<Br^-<I^-. Hence LiCl is least covalent than LiI . The order is LiCl<LiBr<LiI.

(C) Cation size in decreasing order is Na⁺ >Mg²⁺ >Al³⁺. Thus Al³⁺ ion has maximum polarization effect and Na⁺ ion has least. Thus the covalent order is NaCl <MgCl₂<AlCl₃

H₂O is liquid at room temperature but H₂S is gas because hydrogen bonding is present in H₂O and the water molecules get extensively associated in an infinite fashion by weak electrostatic forces. So, H₂O exists as a liquid at room temperature with high boiling point. However, there is no hydrogen bonding in H₂S so it exists as gas.

H₂S is less polar than H₂O because Sulphur is bigger in size and has less electronegativity. So, bp-bp repulsion is less in H₂S as compared to H₂O Hence, bond angle of H − S − H in H₂S, is lesser than H₂O.

It is a weak force of attraction between non-polar molecules like O₂ or N₂ (i.e, between like atoms).

H₂O > H₂S > H₂

sp = 180° 

sp² = 120°

sp³ = 109°28′

CH₄ and CF₄ have tetrahedral structure and are symmetrical, hence their dipole moment is zero, CO₂ is linear and hence its dipole moment is also zero of the remaining CH₃OH and CH₃F, since F is more electronegative than O, CH₃F will have high dipole moment.

In BH₄^- Boron atom is sp³ hybridized and in [PtCl4]^2- platinum is also sp³ hybridized.

(a) 180°

(b) 120°

(c) 109° 28'

The hybrid orbitals used by carbon atoms (from left to right) in the given molecules are

(a) sp³, sp³

(b) sp³, sp², sp²

(c) sp³, sp³

(d) sp³, sp²

(e) sp³, sp²

The process of mixing of the atomic orbitals to form new hybrid orbitals is called hybridization. All hybrid orbitals of a particular kind have equal energy, identical shapes and are symmetrically oriented in shape.

(i) s-hybridized orbitals are oriented in shape at an angle of 180°.

(ii) sp²-hybrid orbitals lie in a plane and directed towards the corners of equilateral triangle with an angle of 120°.

(iii) sp³ hybrid orbitals are directed towards the four corners of a tetrahedron.

Axial bond of PCI₅ are longer as compared to equatorial bond due to great repulsion on axial bond pair electrons by equatorial bond pair electrons.

(i) sp³d

(ii) sp³d²

Bond orders of the different species are:-

O₂ (2.0), O₂⁺ (2.5), O₂^- (1.5), O₂^2- (1.0)

Relative stability: O₂⁺ > O₂ > O₂^- > O₂²

(i) O₂ is paramagnetic

(ii) O₂⁺ is paramagnetic

(iii) O₂^- is paramagnetic

(iv) O₂^2- is diamagnetic

Bonding molecular orbital is formed when the lobes of the combining atomic orbitals have same sign (+ and + or - and -).

Antibonding molecular orbital is formed when the lobes of the combining atomic orbitals have opposite signs (+ and -)

The correct answer is (iv) 4, 0

(a)(i) E

(ii) B

(b) C₂D

(c) A and C are metals while B, D and E are non -metals.

B) G.N. Lewis

(a) Statement I & II are correct and II is the correct explanation of I

The correct option is- (d) NO

The correct option is- (b) H₂

1. In predicting the nature of the molecules: Molecules with specific dipole moments are polar in nature and those with zero dipole moments are non-polar in nature.

2. In the determination of shapes of molecules. 

3. In calculating the percentage of ionic character.

Coulomb^-1 m²

The unit of dipole moment is Coulomb^-1 m².

In the close packed structure of metallic crystal. it contains many slip planes along which movement can occur during mechanical loading, so the metal acquires ductility.