Final answer:
Phosphine does not exhibit hydrogen bonding because the central phosphorus atom does not have the high electronegativity that is required. Phosphorus is less electronegative than nitrogen, oxygen, or fluorine, which are typical atoms involved in hydrogen bonds.
Step-by-step explanation:
Hydrogen bonding is a specific type of intermolecular force that occurs when a hydrogen atom bonded to a highly electronegative atom, such as nitrogen, oxygen, or fluorine, comes into proximity with another electronegative atom. Phosphine (PH3) lacks hydrogen bonding because, while it does contain hydrogen atoms, the central atom is phosphorus, which does not have the required electronegativity to create hydrogen bonds. Phosphorus's electronegativity is lower compared to that of nitrogen, oxygen, or fluorine, and therefore the P-H bonds in phosphine are not sufficiently polar. This results in phosphine being a gas with relatively low boiling and melting points compared to compounds that exhibit hydrogen bonding.
Molecules like boron trihydride (BH3) also exhibit polar bonds, but due to the symmetric arrangement of the molecule, there is no net molecular dipole, and therefore no significant intermolecular attractions like hydrogen bonding. Similarly, in methane (CH4) and propane (C3H8), the molecule is nonpolar due to its symmetry, despite having polarized bonds. Methanol, on the other hand, has an -OH side that is different from the rest, leading to a polar molecule that can engage in hydrogen bonding because of the high electronegativity of oxygen.