1. Hydrogen Bonding:
* Ammonia: Ammonia can form strong hydrogen bonds with water molecules. The highly electronegative nitrogen atom in ammonia attracts the electron pair in the N-H bond, giving the hydrogen atom a partial positive charge. This positive charge interacts strongly with the lone pairs on the oxygen atom of water, forming a hydrogen bond.
* Phosphine: Phosphine, on the other hand, has a much weaker ability to form hydrogen bonds. The phosphorus atom is less electronegative than nitrogen, resulting in a weaker dipole moment and less positive charge on the hydrogen atoms. This leads to weaker interactions with water molecules.
2. Molecular Size and Polarizability:
* Ammonia: Ammonia is a smaller molecule than phosphine, allowing it to better interact with the small water molecules.
* Phosphine: Phosphine is a larger molecule and has a greater polarizability, which means its electron cloud is more easily distorted. This increased polarizability leads to weaker hydrogen bonding and lower solubility.
3. Electronegativity and Polarity:
* Ammonia: The higher electronegativity of nitrogen compared to phosphorus results in a more polar N-H bond in ammonia. This stronger polarity enhances the ability of ammonia to form hydrogen bonds with water.
* Phosphine: The P-H bond in phosphine is less polar, resulting in weaker interactions with water.
4. Bond Strength:
* Ammonia: The N-H bond is stronger than the P-H bond, making it more difficult for ammonia to break apart and dissolve in water.
* Phosphine: The weaker P-H bond in phosphine makes it easier for the molecule to dissociate in water, but this dissociation is not sufficient to overcome the lack of strong hydrogen bonding.
In summary: The combination of stronger hydrogen bonding, smaller size, higher polarity, and stronger N-H bond in ammonia makes it much more soluble in water than phosphine.
