Answer the question on basis of passage given below:
Nitrogen differs from the rest of the members of its group due to its small size, high electronegativity, high ionisation enthalpy and non-availability of d-orbitals. Nitrogen has unique ability to form $pπ-pπ$ multiple bonds with itself and with other elements having small size and high electronegativity (eg, C, O) Heavier elements of this group do not form $pπ-pπ$ bonds as their atomic orbitals are so large and diffused that they cannot have effective overlapping.
Most stable hydride amongst the following is:
(A) $NH_3$
(B) $PH_3$
(C) $AsH_3$
(D) $SbH_3$
(E) $BiH_3$
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 1
The correct answer is Option 1. (A) Only.
The stability of hydrides, particularly those of the nitrogen group (Group 15 elements), can be understood by examining several factors: bond strength, molecular geometry, electronegativity, and hydrogen bonding.
Overview of Hydrides
The hydrides of Group 15 elements include:
\(NH_3\) (Ammonia)
\(PH_3\) (Phosphine)
\(AsH_3\) (Arsine)
\(SbH_3\) (Stibine)
\(BiH_3\) (Bismuth Hydride)
As you move down the group from nitrogen to bismuth, the stability of the hydrides generally decreases. Here’s a detailed analysis of each:
A. \(NH_3\) (Ammonia)
Bonding and Geometry: Ammonia has a trigonal pyramidal geometry due to the presence of a lone pair on nitrogen. The N-H bond is relatively short and strong.
Hydrogen Bonding: \(NH_3\) can form hydrogen bonds due to the high electronegativity of nitrogen, leading to a higher boiling point and increased stability.
Stability: It is the most stable hydride in this group, with a boiling point of -33.3°C.
B. \(PH_3\) (Phosphine)
Bonding and Geometry: Phosphine has a similar geometry but with larger bond lengths due to the larger size of phosphorus compared to nitrogen.
Weaker Bonds: The P-H bonds are weaker than N-H bonds, which results in lower stability. Phosphine does not form significant hydrogen bonds.
Stability: Less stable than NH₃, with a boiling point of -87.7°C.
C. \(AsH_3\) (Arsine)
Bonding and Geometry: Arsine continues the trend with larger bond lengths and weaker As-H bonds.
Lack of Hydrogen Bonding: Similar to phosphine, arsine does not form hydrogen bonds effectively.
Stability: Even less stable than phosphine, with a boiling point of -62°C
D. \(SbH_3\) (Stibine)
Bonding and Geometry: Stibine has even weaker Sb-H bonds due to the increased size and lower electronegativity of antimony.
Lack of Hydrogen Bonding: Stibine exhibits poor hydrogen bonding capability.
Stability: Less stable than arsine, with a boiling point of -17.4°C.
E. \(BiH_3\) (Bismuth Hydride)
Bonding and Geometry: Bismuth hydride has the weakest Bi-H bonds due to the significant increase in atomic size and the decrease in bond strength as you move down the group.
Very Weak Bonds: The Bi-H bonds are considerably weaker than those in the other hydrides.
Stability: The least stable of the hydrides, with a boiling point of 50.2°C, though it decomposes rather than vaporizes under normal conditions.
Thus, among the options provided, the most stable hydride is (A) Only \((NH_3)\) due to its strong N-H bonds and the ability to engage in hydrogen bonding.