The high boiling point of hydrogen fluoride can be explained in terms of
A. covalent bonds.
B. dative bonds.
C. dipole-dipole bonds.
D. electrovalent (ionic) bonds.
E. hydrogen bonds.
The correct answer is E. hydrogen bonds.
Explanation:
The high boiling point of hydrogen fluoride can be explained in terms of hydrogen bonds.
Hydrogen fluoride (HF) has a high boiling point due to the presence of hydrogen bonds. These are not to be confused with covalent bonds, dative bonds, dipole-dipole bonds, or electrovalent (ionic) bonds in the other options.
Hydrogen bonding is a special type of intermolecular force that exists when hydrogen is bonded to a strong electronegative atom. It exist between a hydrogen atom in a polar molecule and an electronegative atom usually nitrogen, oxygen, or fluorine in the same or a different molecule.
This bond is significantly stronger than other kinds of intermolecular forces like dipole-dipole interactions or van der Waals forces, which leads to higher boiling points.
In the case of hydrogen fluoride, the hydrogen atom is bonded to a very strong electronegative fluorine atom. The resulting strong polarity of the HF molecule leads to strong attractive forces i.e. hydrogen bond between the hydrogen atom of one molecule and the fluorine atom of a neighboring molecule. These strong forces need a lot of heat energy to be broken, hence the lead to the high boiling point of Hydrogen Fluoride.
On the other hand, covalent bonds are the bonds within the Hydrogen Fluoride molecule itself, not between different Hydrogen Fluoride molecules.
Dative bonds are a type of covalent bond where both electrons come from the same atom, which is not the case in Hydrogen Fluoride. Dipole-dipole bonds are intermolecular forces that exist between polar molecules, but they are not as strong as hydrogen bonds. Electrovalent (ionic) bonds are formed between atoms that have lost or gained electrons, which is also not the case for Hydrogen Fluoride.
SOURCE: NECO CHEMISTRY 2001 QUESTION 28
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