Question

Which species cannot be formed unless the central atom exceeds an octet? Select the best answer as listed below

i. Xef2
II. SbCls
III. PCl3
IV. NH3

a) only ll
b) both I and Il
c) only IV
d) both I and 11
d) only IlI
e) only D

Answer 1

The species in which the central atom must exceed an octet are Xenon difluoride (XeF2) and Antimony pentachloride (SbCl5), as both xenon and antimony have d orbitals that allow them to hold more than eight electrons.

Step-by-step explanation:

The question posed by the student is concerned with which species can only be formed if the central atom in the molecule exceeds an octet of electrons. Molecules that exceed the octet rule typically have a central atom that is in period 3 or beyond in the periodic table, as these elements have d orbitals that can be used for bonding. The student provided several molecular formulae and asked to select the species which cannot form unless the central atom exceeds an octet.

Among the options given to the student (XeF2, SbCl5, PCl3, NH3), XeF2 (Xenon difluoride) and SbCl5 (Antimony pentachloride) are the molecules where the central atom exceeds an octet. Xenon and antimony are elements that are able to hold more than eight electrons in their valence shells due to the availability of d orbitals. Therefore, the correct answer is (b) both I and II.

Answer 2

Compounds XeF2 and SbCl5 require the central atom to exceed an octet due to the presence of d orbitals, which is not the case with PCl3 and NH3. Therefore, the correct answer is (d) both I and II.

Step-by-step explanation:

The question relates to identifying compounds where the central atom exceeds the typical octet found in the second-period elements, a phenomenon often referred to as an expanded octet. Only the central atoms from the third period onwards can achieve this due to the availability of d orbitals for bonding. Molecules like XeF2 (where Xenon is the central atom) and SbCl5 (where Antimony is the central atom) require the central atom to exceed an octet of electrons.

Molecules such as PCl3 (where Phosphorus is the central atom) and NH3 (Ammonia, where Nitrogen is the central atom) do not need to exceed an octet as they can accomplish stable electronic configurations with eight or fewer electrons surrounding the central atom. Based on this knowledge, the correct option for the given question would be (d) both I and II, meaning both XeF2 and SbCl5 cannot be formed unless the central atom exceeds an octet.