Ch.22 - The Main Group Elements

McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook

McMurry 8th Edition

Ch.22 - The Main Group Elements

Problem 22.113

Chapter 22, Problem 22.113

Compare and contrast the properties of ammonia and phosphine.

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Identify the chemical formulas for ammonia and phosphine: Ammonia is NH₃ and phosphine is PH₃.

Compare the molecular geometry: Both ammonia and phosphine have a trigonal pyramidal shape due to the presence of a lone pair on the nitrogen and phosphorus atoms, respectively.

Discuss the polarity: Ammonia is polar due to the difference in electronegativity between nitrogen and hydrogen, while phosphine is less polar because the electronegativity difference between phosphorus and hydrogen is smaller.

Examine the hydrogen bonding: Ammonia can form hydrogen bonds due to the presence of highly electronegative nitrogen, whereas phosphine cannot form hydrogen bonds as effectively because phosphorus is less electronegative.

Compare the boiling points: Ammonia has a higher boiling point than phosphine due to the presence of hydrogen bonding, which requires more energy to break compared to the weaker van der Waals forces in phosphine.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molecular Structure and Polarity

Ammonia (NH3) and phosphine (PH3) have distinct molecular structures that influence their properties. Ammonia has a trigonal pyramidal shape due to the presence of a lone pair on nitrogen, making it polar and capable of hydrogen bonding. In contrast, phosphine has a similar structure but is less polar due to phosphorus's larger size and lower electronegativity, resulting in weaker intermolecular forces.

Boiling Points and Volatility

The boiling points of ammonia and phosphine differ significantly due to their molecular interactions. Ammonia has a higher boiling point (−33.34 °C) because of strong hydrogen bonds, while phosphine has a lower boiling point (−87.7 °C) due to weaker van der Waals forces. This difference in boiling points reflects their volatility and stability as gases at room temperature.

Reactivity and Chemical Behavior

Ammonia and phosphine exhibit different reactivities due to their molecular characteristics. Ammonia is a strong base and can readily donate a proton, participating in various acid-base reactions. Phosphine, on the other hand, is less basic and more stable, making it less reactive under similar conditions. This difference affects their roles in chemical reactions and their applications in various fields.

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