Question

Which of the following hydrogen bonds is the strongest? \(\quad\) (a) \(\mathrm{F}-\mathrm{H} \ldots . \mathrm{F}\) (b) \(\mathrm{O}-\mathrm{H} \ldots \mathrm{O}\) (c) \(\mathrm{O}-\mathrm{H} \ldots \mathrm{F}\) (d) \(\mathrm{O}-\mathrm{H}_{\ldots} . \mathrm{N}\)

Short answer

(a) \(\mathrm{F}-\mathrm{H} \ldots . \mathrm{F}\) is the strongest hydrogen bond, given fluorine's high electronegativity.

Step-by-step solution

Identify the Principles of Hydrogen Bond Strength

Hydrogen bonds occur when a hydrogen atom covalently bonded to a highly electronegative atom, like fluorine (F), oxygen (O), or nitrogen (N), forms a weak interaction with another electronegative atom. The strength of a hydrogen bond depends on the electronegativity of the involved atoms and the hydrogen atom's partial positive charge. Generally, the greater the electronegativity difference, the stronger the hydrogen bond.

Analyze each Option

Let's analyze the given options individually: - In (a) \(\mathrm{F}-\mathrm{H} \ldots . \mathrm{F}\), the hydrogen is bonded to fluorine, the most electronegative element, creating a very strong dipole.- In (b) \(\mathrm{O}-\mathrm{H} \ldots \mathrm{O}\), the hydrogen is bonded to oxygen, which is highly electronegative but less so than fluorine.- In (c) \(\mathrm{O}-\mathrm{H} \ldots \mathrm{F}\), the interaction involves oxygen and fluorine, but the hydrogen originates from an oxygen atom.- In (d) \(\mathrm{O}-\mathrm{H}_{\ldots} . \mathrm{N}\), it involves nitrogen, which is highly electronegative but less than fluorine and oxygen.

Compare and Determine the Strongest Bond

Based on the electronegativities, fluorine is the most electronegative element, resulting in the strongest hydrogen bond. Therefore, in option (a) \(\mathrm{F}-\mathrm{H} \ldots . \mathrm{F}\), both hydrogen and its adjacent electronegative partner are fluorine atoms, leading to the greatest electronegativity difference and the strongest bond.

Key concepts

Electronegativity

Electronegativity is a measure of an atom's ability to attract and hold onto electrons. Imagine it as a tug-of-war, with each atom pulling on the electron cloud. The stronger the pull, the more electronegative the atom is. In the periodic table, electronegativity values increase as you move from left to right across a period and decrease as you move down a group.

Fluorine stands as the most electronegative element, followed by oxygen and nitrogen. Their high electronegativity allows them to form strong hydrogen bonds, which are actually a special kind of dipole-dipole interaction. When hydrogen bonds with these elements, the electronegativity difference creates a partial positive charge on hydrogen and a partial negative charge on the other atom. This difference is crucial because the larger the difference in electronegativity, the stronger the hydrogen bond formed. Fluorine, being the most electronegative, can create the strongest hydrogen bonds due to this high electronegativity difference.

Intermolecular Forces

Intermolecular forces are the invisible threads that hold molecules together. These forces include hydrogen bonds, dipole-dipole interactions, and van der Waals forces. They are not as strong as the bonds within a molecule but play a crucial role in determining the properties of substances, like boiling and melting points.

Among these, hydrogen bonding is particularly strong and significant. In hydrogen bonding, a hydrogen atom covalently bonded to a more electronegative atom forms a bond with another electronegative atom. This results in unique properties, such as water's high surface tension and its ability to dissolve many substances.

• Hydrogen bonds rely heavily on electronegativity, where the hydrogen attaches to atoms like F, O, or N, known for their high electronegativity.
• The arrangement of the atoms plays a role, with the linear alignment of atoms creating a stronger bond.

These characteristics make hydrogen bonds the strongest among intermolecular forces, providing them with a key role in many biological and chemical processes.

Chemical Bond Strength

The strength of chemical bonds largely dictates how substances interact with each other, impacting everything from stability to reactivity. Bond strength is commonly evaluated by the energy required to break a bond.

In the realm of hydrogen bonding, bond strength is highly influenced by the electronegativity of the atoms involved. For example, in the options given \( ext{a, b, c, d} \), the hydrogen bond between \( ext{F}- ext{H} \) is the strongest because of fluorine's high electronegativity. This strong pull results in a robust bond:

• The greater the electronegativity, the stronger the partial charge differences, leading to a stronger bond.
• Covalent bonds within the molecule can influence the strength of formed hydrogen bonds externally.
• Hydrogen bonds are generally weaker than covalent or ionic bonds but are the strongest among the forces acting between molecules.

Understanding this hierarchy of bond strength can explain why certain substances exhibit particular physical or chemical behaviors. Knowing about electronegativity helps predict the strength and behavior of these bonds, making it indispensable in predicting molecular interactions and compound properties.