According to experimentalfindings, all carbon to oxygen bonds in are equivalent. Hence, it isinadequate to represent ion by a single Lewis structurehaving two single bonds and one double bond.

Therefore, carbonate ionis described as a resonance hybrid of the following structures:

Question - 12 : -
H₃PO₃ can berepresented by structures 1 and 2 shown below. Can these two structures betaken as the canonical forms of the resonance hybrid representing H₃PO₃?If not, give reasons for the same.

Answer - 12 : -

Thegiven structures cannot be taken as the canonical forms of the resonance hybridof H₃PO₃ because thepositions of the atoms have changed.

Question - 13 : -
Write the resonance structures for SO₃, NO₂ and.

Answer - 13 : -

The resonance structuresare:

(a) SO₃:

(b)

Question - 14 : -
UseLewis symbols to show electron transfer between the following atoms to formcations and anions: (a) K and S (b) Ca and O (c) Al and N.

Answer - 14 : -

(a) K and S:

The electronicconfigurations of K and S are as follows:

K: 2, 8, 8, 1

S: 2, 8, 6

Sulphur (S) requires 2more electrons to complete its octet. Potassium (K) requires one electron morethan the nearest noble gas i.e., Argon. Hence, the electron transfer can beshown as:

(b) Ca and O:

The electronicconfigurations of Ca and O are as follows:

Ca: 2, 8, 8, 2

O: 2, 6

Oxygen requires twoelectrons more to complete its octet, whereas calcium has two electrons morethan the nearest noble gas i.e., Argon. Hence, the electron transfer takesplace as:

(c) Al and N:

The electronicconfigurations of Al and N are as follows:

Al: 2, 8, 3

N: 2, 5

Nitrogen is threeelectrons short of the nearest noble gas (Neon), whereas aluminium has threeelectrons more than Neon. Hence, the electron transference can be shown as:

Question - 15 : -
Although both CO₂ and H₂O are triatomic molecules,the shape of H₂O molecule is bent while that of CO₂ is linear. Explainthis on the basis of dipole moment.

Answer - 15 : -

According to experimentalresults, the dipole moment of carbon dioxide is zero. This is possible only ifthe molecule is linear so that the dipole moments of C–O bonds are equal andopposite to nullify each other.

Resultant μ = 0 D

H₂O, on the other hand, hasa dipole moment value of 1.84 D (though it is a triatomic molecule as CO₂). The value of the dipolemoment suggests that the structure of H₂O molecule is bent wherethe dipole moment of O–H bonds are unequal.

Question - 16 : -
Writethe significance/applications of dipole moment.

Answer - 16 : -

In heteronuclearmolecules, polarization arises due to a difference in the electronegativitiesof the constituents of atoms. As a result, one end of the molecule acquires apositive charge while the other end becomes negative. Hence, a molecule is saidto possess a dipole.

The product of the magnitude of the chargeand the distance between the centres of positive-negative charges is called thedipole moment (μ) of the molecule. It is a vector quantity and isrepresented by an arrow with its tail at the positive centre and head pointingtowards a negative centre.

Dipole moment (μ) = charge (Q) ×distance of separation (r)

The SI unit of a dipolemoment is ‘esu’.

1 esu = 3.335 × 10^–30 Cm

Dipole moment is the measure of the polarityof a bond. It is used to differentiate between polar and non-polar bonds sinceall non-polar molecules (e.g. H₂, O₂) have zero dipolemoments. It is also helpful in calculating the percentage ionic character of amolecule.

Question - 17 : -
Defineelectronegativity. How does it differ from electron gain enthalpy?

Answer - 17 : -

Electronegativity is theability of an atom in a chemical compound to attract a bond pair of electronstowards itself.

Electronegativity of anygiven element is not constant. It varies according to the element to which itis bound. It is not a measurable quantity. It is only a relative number.

Onthe other hand, electron gain enthalpy is the enthalpy change that takes placewhen an electron is added to a neutral gaseous atom to form an anion. It can benegative or positive depending upon whether the electron is added or removed.An element has a constant value of the electron gain enthalpy that can bemeasured experimentally.

Question - 18 : -
Explainwith the help of suitable example polar covalent bond.

Answer - 18 : -

When two dissimilar atomshaving different electronegativities combine to form a covalent bond, the bondpair of electrons is not shared equally. The bond pair shifts towards thenucleus of the atom having greater electronegativity. As a result, electrondistribution gets distorted and the electron cloud is displaced towards theelectronegative atom.

As a result, theelectronegative atom becomes slightly negatively charged while the other atombecomes slightly positively charged. Thus, opposite poles are developed in themolecule and this type of a bond is called a polar covalent bond.

HCl, for example, containsa polar covalent bond. Chlorine atom is more electronegative than hydrogenatom. Hence, the bond pair lies towards chlorine and therefore, it acquires apartial negative charge.

Question - 19 : -
Arrange the bonds in order of increasingionic character in the molecules: LiF, K₂O, N₂, SO₂ and ClF₃.

Answer - 19 : -

The ionic character in amolecule is dependent upon the electronegativity difference between theconstituting atoms. The greater the difference, the greater will be the ioniccharacter of the molecule.

On this basis, the orderof increasing ionic character in the given molecules is

N₂ < SO₂ < ClF₃ < K₂O < LiF.

Question - 20 : -
The skeletal structure of CH₃COOH as shown below iscorrect, but some of the bonds are shown incorrectly. Write the correct Lewisstructure for acetic acid.

Answer - 20 : -

The correct Lewis structurefor acetic acid is as follows:

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