Question

Among \(\mathrm{NH}_{3}, \mathrm{H}_{2} \mathrm{O}\) and \(\mathrm{HF}\), which would you expect to have highest magnitude of hydrogen bonding and why?

Short answer

\(\mathrm{HF}\) has the highest magnitude of hydrogen bonding due to fluorine's high electronegativity and small size.

Step-by-step solution

Identify the Molecules

First, look at the three molecules we need to compare: \(\mathrm{NH}_{3}\), \(\mathrm{H}_{2} \mathrm{O}\), and \(\mathrm{HF}\). All of these molecules can form hydrogen bonds due to the presence of hydrogen (H) atoms bonded to highly electronegative atoms (N, O, or F).

Understand the Basic Hydrogen Bonding Concept

Hydrogen bonding occurs when a hydrogen atom, which is covalently bonded to a highly electronegative atom such as nitrogen, oxygen, or fluorine, interacts with another electronegative atom. The strength of hydrogen bonding increases with greater electronegativity and smaller atomic size of the electronegative atom.

Evaluate Electronegativity and Atomic Size

Compare the electronegativity of the atoms bonded to hydrogen: Fluorine (F) is the most electronegative, followed by oxygen (O), and then nitrogen (N). The higher the electronegativity, the stronger the hydrogen bonding tends to be. Additionally, a smaller atomic size leads to stronger hydrogen bonding due to closer proximity.

Predict the Strongest Hydrogen Bond

Among \(\mathrm{NH}_{3}\), \(\mathrm{H}_{2} \mathrm{O}\), and \(\mathrm{HF}\), \(\mathrm{HF}\) is expected to exhibit the strongest hydrogen bonding because fluorine has the highest electronegativity and is the smallest atom among N, O, and F, leading to stronger attractions in the hydrogen bond.

Key concepts

Electronegativity

Electronegativity refers to the ability of an atom to attract shared electrons in a chemical bond. In our context, electronegativity is crucial because it determines how strongly the hydrogen atom is attracted to the electronegative atom it is bonded with, such as N, O, or F.
Among these atoms, fluorine has the highest electronegativity, which means it pulls on shared electrons more strongly than either oxygen or nitrogen. This strong attraction results in a larger dipole moment across the molecule, creating a stronger hydrogen bond.
In \(HF\), the high electronegativity of fluorine means that the shared electrons between hydrogen and fluorine are more influenced by the fluorine, leading to a partial negative charge on the fluorine and a partial positive charge on the hydrogen. This partial charge separation enhances the ability of HF to form strong hydrogen bonds with other electronegative atoms.

Atomic Size

Atomic size refers to the physical size of the atom, usually determined by the boundary of the electron cloud surrounding the nucleus. In hydrogen bonding, a smaller atomic size is beneficial for strong interactions because the smaller the atom, the closer it can get to the proton in hydrogen.
Fluorine, being the smallest atom among nitrogen, oxygen, and itself, contributes to HF forming the strongest hydrogen bonds. Being smaller, it allows the bond to be shorter, and shorter bonds are generally stronger due to applying more force per distance on the interacting atoms.
Therefore, the combination of high electronegativity and small atomic size makes fluorine in HF create extremely strong hydrogen bonds, stronger than those in NH\(3\) or H\(2\)O.

Intermolecular Forces

Intermolecular forces are forces of attraction or repulsion which act between neighboring particles (atoms, molecules, or ions). Hydrogen bonding is a type of intermolecular force that occurs between hydrogen attached to an electronegative atom and another electronegative atom.
These forces are important because they affect the physical properties of substances, such as boiling points and solubilities. Molecules with stronger hydrogen bonds have higher boiling points because more energy is required to break the strong hydrogen bonds.
In the case of HF, its intermolecular forces are stronger due to its potent hydrogen bonds. This results from the combined effect of fluorine's high electronegativity and small size, leading HF to have higher boiling points compared to NH\(3\) and H\(2\)O. These robust interactions between HF molecules showcase the significance of intermolecular forces influenced by atomic characteristics.