Isostructural species are those which have the same shape and hybridization. Among the given species, identify the isostructural pairs.

• a.) NF₃ and BF₃
• b.) BF₄⁻ and NH₄⁺
• c.) BCl₃ and BrCl₃
• d.) NH₃ and NO₃⁻

To determine which pairs of species are isostructural, we need to analyze their molecular geometries and hybridizations. Isostructural species share the same shape and hybridization, which means they have similar bonding arrangements and electron pair geometries. Let's break down each pair you provided.

Analyzing Each Pair

a.) NF₃ and BF₃

Both nitrogen trifluoride (NF₃) and boron trifluoride (BF₃) have a trigonal planar geometry. However, their hybridizations differ. NF₃ is sp³ hybridized due to the presence of a lone pair on nitrogen, while BF₃ is sp² hybridized as it has no lone pairs. Therefore, these two are not isostructural.

b.) BF₄⁻ and NH₄⁺

Both tetrafluoroborate (BF₄⁻) and ammonium (NH₄⁺) ions exhibit a tetrahedral geometry. Their hybridization is also the same: sp³. Since they share both shape and hybridization, BF₄⁻ and NH₄⁺ are indeed isostructural.

c.) BCl₃ and BrCl₃

Boron trichloride (BCl₃) and bromine trichloride (BrCl₃) both have a trigonal planar structure. However, the hybridization of BCl₃ is sp², while BrCl₃ is also sp² but has a different central atom. Although they have the same geometry, the difference in central atoms and their electronegativities can lead to variations in bond angles and lengths. Thus, they are not considered isostructural.

d.) NH₃ and NO₃⁻

Ammonia (NH₃) has a trigonal pyramidal shape due to the presence of a lone pair on nitrogen, and its hybridization is sp³. In contrast, the nitrate ion (NO₃⁻) has a trigonal planar geometry with sp² hybridization, as it has resonance structures and no lone pairs on the central nitrogen. Therefore, NH₃ and NO₃⁻ are not isostructural.

Summary of Findings

• NF₃ and BF₃: Not isostructural
• BF₄⁻ and NH₄⁺: Isostructural
• BCl₃ and BrCl₃: Not isostructural
• NH₃ and NO₃⁻: Not isostructural

In conclusion, the only isostructural pair among the options provided is BF₄⁻ and NH₄⁺. Understanding these concepts helps in predicting molecular behavior and reactivity based on structure, which is fundamental in chemistry.