Chapter 16: Problem 143
Which of the following is a stronger base: \(\mathrm{NH}_{3}\) or \(\mathrm{PH}_{3}\) ? (Hint: The \(\mathrm{N}-\mathrm{H}\) bond is stronger than the \(\mathrm{P}-\mathrm{H}\) bond. \()\)
Short Answer
Expert verified
\( \mathrm{NH}_3 \) is the stronger base.
Step by step solution
Over 22 million students worldwide already upgrade their learning with Vaia!
Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Ammonia (NH3)
Ammonia, with the chemical formula \( \mathrm{NH}_3 \), is a fascinating compound that's quite commonly encountered in the realm of acid-base chemistry. It is a simple nitrogen hydride, meaning that it consists of one nitrogen atom bonded to three hydrogen atoms. This structure gives ammonia a unique geometry called trigonal pyramidal.
Ammonia is notable for its ability to behave as a base, which is due to the lone pair of electrons on the nitrogen atom. The nitrogen atom in ammonia is quite willing to share its lone pair with a proton (\( \mathrm{H}^+ \)), making it an effective base. This ability to donate the lone pair is what makes ammonia a strong base compared to many other compounds. Furthermore, the strong \( \mathrm{N-H} \) bonds contribute to the stability of ammonia, allowing it to form stable bonds with protons when acting as a base.
Ammonia is notable for its ability to behave as a base, which is due to the lone pair of electrons on the nitrogen atom. The nitrogen atom in ammonia is quite willing to share its lone pair with a proton (\( \mathrm{H}^+ \)), making it an effective base. This ability to donate the lone pair is what makes ammonia a strong base compared to many other compounds. Furthermore, the strong \( \mathrm{N-H} \) bonds contribute to the stability of ammonia, allowing it to form stable bonds with protons when acting as a base.
Phosphine (PH3)
Phosphine, represented by the formula \( \mathrm{PH}_3 \), is another compound that can act as a base, though it is significantly less effective than ammonia. Like ammonia, phosphine also has a trigonal pyramidal structure, but it is a phosphorus hydride, as it includes a central phosphorus atom bonded to three hydrogens.
Unlike ammonia, phosphine is not as proficient in donating its lone pair. This is predominantly because the phosphorus atom is less electronegative than the nitrogen atom, which affects its ability to hold onto and donate its electrons. Moreover, the \( \mathrm{P-H} \) bonds are weaker than \( \mathrm{N-H} \) bonds, rendering phosphine a less stable and hence weaker base than ammonia. As a result, while phosphine can act as a base, it does so less robustly than ammonia.
Unlike ammonia, phosphine is not as proficient in donating its lone pair. This is predominantly because the phosphorus atom is less electronegative than the nitrogen atom, which affects its ability to hold onto and donate its electrons. Moreover, the \( \mathrm{P-H} \) bonds are weaker than \( \mathrm{N-H} \) bonds, rendering phosphine a less stable and hence weaker base than ammonia. As a result, while phosphine can act as a base, it does so less robustly than ammonia.
Electronegativity
Electronegativity is a measure of an atom's ability to attract and hold onto electrons. It plays a vital role in determining the behavior of compounds in acid-base reactions. In the context of ammonia and phosphine, the electronegativity of the central atom is crucial.
Nitrogen, the central atom of ammonia, has a higher electronegativity compared to phosphorus, which is the central atom in phosphine. The higher electronegativity of nitrogen makes it more capable of attracting electrons, thereby making its lone pair more available for donation. This contributes to ammonia being a stronger base compared to phosphine. In contrast, phosphine's lower electronegativity makes it less effective at attracting and donating its lone pair electrons, resulting in weaker basicity.
Nitrogen, the central atom of ammonia, has a higher electronegativity compared to phosphorus, which is the central atom in phosphine. The higher electronegativity of nitrogen makes it more capable of attracting electrons, thereby making its lone pair more available for donation. This contributes to ammonia being a stronger base compared to phosphine. In contrast, phosphine's lower electronegativity makes it less effective at attracting and donating its lone pair electrons, resulting in weaker basicity.
Lone Pair Donation
The ability to donate lone pairs of electrons is a key characteristic that determines whether a compound can effectively act as a base. In both \( \mathrm{NH}_3 \) and \( \mathrm{PH}_3 \), the central atoms have one lone pair of electrons each. However, not all lone pairs are equally willing to be donated.
Ammonia's lone pair, residing on the nitrogen atom, is more available for donation. This is due to nitrogen's higher electronegativity and the stronger \( \mathrm{N-H} \) bonds, making its lone pair electrons less shielded and more reactive. Conversely, in phosphine, the lone pair is held more "tightly" due to phosphorus's lower electronegativity, making it less available for reaction with protons. Therefore, when it comes to acting as a base, ammonia outshines phosphine due to more effective lone pair donation.
Ammonia's lone pair, residing on the nitrogen atom, is more available for donation. This is due to nitrogen's higher electronegativity and the stronger \( \mathrm{N-H} \) bonds, making its lone pair electrons less shielded and more reactive. Conversely, in phosphine, the lone pair is held more "tightly" due to phosphorus's lower electronegativity, making it less available for reaction with protons. Therefore, when it comes to acting as a base, ammonia outshines phosphine due to more effective lone pair donation.
