(a) Draw the molecular structures of the following compounds:
(i) N₂O₅
(ii)XeOF₄.
(b) Explain the following observations:
(i) Sulphur has a greater tendency for catenation than oxygen.
(ii)I-Cl is more reactive than I₂.
(iii)Despite lower value of its electron gain enthalpy with negative sign, fluorine (F₂) is a stronger oxidizing agent than Cl₂.
OR
(a) Complete the following chemical equations:

(b)Explain the following observations :
(i)Phosphorus has greater tendency for catenation than nitrogen.
(ii)Oxygen is a gas but sulphur a solid.
(iii)The halogens are coloured. Why?

(a)

(i)

Structure of N₂O₅.

(ii)

Structure of XeOF₄.

(b)

(i)

• Catenation (i.e. linking of atoms of the same kind with one another) is related to the atom-atom bond energy.

• Greater the atom-atom bond energy, greater is the catenation. Higher the stability of single bond between the same atom, more will be the affinity to undergo catenation.

• S-S bond is stronger than O-O bond and sulphur has an extra d orbital present.

• Oxygen atom is smaller in size as compared to sulphur due to lone pair of electrons in O-O bonds in oxygen experiences more repulsions as compared to the S-S bonds and thus, S-S forms strong bond. So, sulphur shows greater tendency for catenation than oxygen.

Catenation in carbon

(ii)

• An interhalogen compound is a compound which contains two or more different halogen atoms and no atoms of elements from any other group.

• Because of its partly ionic character due to difference in electronegativities, inter halogen bonds are weaker.

• When similar halogens form X₂(where X is the halogen atom) molecules, they form covalent bonds which are stronger than interhalogen compounds with different halogen which form weak bonds.

• Due the formation of these weak bonds, ICl is more reactive than I₂.

Examples of interhalogen compounds are IF_7, ICl, BrF₃, etc.

(iii) The electron gain enthalpy of chlorine is more negative than that of fluorine. However, the bond dissociation energy of fluorine is much lesser than that of chlorine. Fluorine is a stronger oxidizing agent than chlorine, because of

1. Low enthalpy of dissociation of F-F bond.

2. Due to its small size, fluorine's hydration energy is very high and so its oxidizing power is higher.

ii. High hydration enthalpy of fluorine. Fluorine has greater electron-electron repulsion amongst the lone pairs in the small sized molecule where they are much closer to each other than in chlorine. Thus the enthalpy of dissociation of fluorine is lower than chlorine which makes it better oxidizing agent.

OR

(a)

(i)

(ii)

(b)

• Catenation (i.e. linking of atoms of the same kind with one another) is related to the atom-atom bond energy. Greater the atom-atom bond energy, greater is the catenation.

• Higher the stability of single bond between the same atom more will be the affinity to undergo catenation.

• As nitrogen atom is smaller, there is greater repulsion of electron density of two nitrogen atoms, which in turn weaken the N–N bond and decreases the tendency of nitrogen to show catenation.

• So, N–N is much weaker than P-P bond due to the presence more repulsion of lone pairs on nitrogen atom as compared to the P–P bond lone pairs.

• Because of this low N-N bond energy, nitrogen shows little tendency for catenation. Whereas, P-P bond energy is quite high, hence, it shows more tendency for catenation than nitrogen.

Catenation in carbon

(iii) We know, oxygen is smaller in size as compared to sulphur. Due to its smaller size, oxygen can effectively form pπ-pπ bonds and form O₂ molecule. Since the intermolecular forces in oxygen are weak van der Wall's forces, oxygen exist as gas. On the other hand, sulphur does not form S₂ molecule but exists as a structure held together by strong covalent bonds. Hence, it is a solid.

(iii)

Halogens are coloured. This is because:

• They absorb radiations in the visible region of the spectrum.

• This results in the excitation of valence electrons to a higher energy region.

• For different halogens, amount of energy required for excitation differs, so each halogen displays a different colour.