Types and Properties of Hydrogen Bonding

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Types and Properties of Hydrogen Bonding

This lesson aligns with NGSS PS1.A

Introduction

A hydrogen bond is a unique form of dipole-dipole attraction. It arises when a hydrogen atom, covalently bonded to a highly electronegative atom, is in proximity to another electronegative atom possessing a lone pair of electrons. While these bonds exhibit greater strength compared to typical dipole-dipole and dispersion forces, they are comparatively weaker than true covalent and ionic bonds. For instance, in water molecules (

$H_2O$ ), hydrogen is covalently bonded to the more electronegative oxygen atom. In this article, we will delve into the properties of hydrogen bond, types of hydrogen bond, effect of hydrogen bonding on elements as well as the conditions for hydrogen bonding.

Properties of Hydrogen Bond

Solubility:

Lower alcohols exhibit solubility in water due to the occurrence of hydrogen bonding between water and alcohol molecules.

Volatility:

Compounds that involve hydrogen bonding between different molecules tend to have higher boiling points, resulting in lower volatility.

Viscosity and Surface Tension:

Substances with hydrogen bonding exist as associated molecules, leading to increased difficulty in flow. They possess higher viscosity and elevated surface tension.

Lower Density of Ice than Water:

In solid ice, hydrogen bonding contributes to a cage-like structure of water molecules, with each water molecule linked tetrahedrally to four others. This arrangement results in a less closely packed structure compared to the liquid state.

When ice undergoes melting, this cage-like structure collapses, causing the molecules to approach each other more closely. Consequently, for the same mass of water, the volume decreases, leading to increased density. Hence, at 273 K, ice exhibits lower density than water, explaining its ability to float.

Types of Hydrogen Bonding

There are two types of H-bond which are classified as intermolecular hydrogen bonding and intramolecular hydrogen bonding.

Intermolecular Hydrogen Bonding

When hydrogen bonding occurs between different molecules, whether they belong to the same or different compounds, it is referred to as intermolecular hydrogen bonding.

Examples include hydrogen bonding in water, alcohol, ammonia, etc.

Intramolecular Hydrogen Bonding

Intramolecular hydrogen bonding occurs within a molecule itself.

This type of bonding takes place in compounds containing two groups, where one group has a hydrogen atom linked to an electronegative atom, and the other group contains a highly electronegative atom linked to a less electronegative atom within the same group.

The bond is formed between the hydrogen atoms of one group and the more electronegative atom of the other group.

Conditions for Hydrogen Bonding

Hydrogen bonding results in a hydrogen atom simultaneously forming a covalent bond with one electronegative atom and a hydrogen bond with another. The conditions necessary for hydrogen bonding include:

The molecule must contain a highly electronegative atom connected to the hydrogen atom. Higher electronegativity results in increased molecule polarization.
The electronegative atom should have a small size. A smaller size enhances electrostatic attraction.

Effects of Hydrogen Bonding on Elements

Association:

Carboxylic acid molecules tend to associate and form dimers due to hydrogen bonding. This association leads to molecular masses of these compounds being double than those calculated from their simple formulas.

Dissociation:

In an aqueous solution, HF undergoes dissociation and produces the difluoride ion instead of the fluoride ion. This unique behavior is attributed to hydrogen bonding in HF. On the contrary, molecules of HCl, HBr, and HI do not form hydrogen bonds, explaining the absence of compounds like

$KHCl_2$ ,

$KHBr_2$ , and

$KHI_2$ .

Hydrogen Bond Donor and Acceptor

In a hydrogen bond, the donor typically consists of a strongly electronegative atom like nitrogen (N), oxygen (O), or fluorine (F), which is covalently bonded to a hydrogen atom. Conversely, the hydrogen acceptor is an electronegative atom from an adjacent molecule, possessing a lone pair engaged in the hydrogen bond, such as O, N, Cl, and F.

Summary

Lower alcohols exhibit solubility in water due to the occurrence of hydrogen bonding between water and alcohol molecules.
Compounds that involve hydrogen bonding between different molecules tend to have higher boiling points, resulting in lower volatility.
Substances with hydrogen bonding exist as associated molecules, leading to increased difficulty in flow. They possess higher viscosity and elevated surface tension.
There are two types of H-bond which are classified as intermolecular hydrogen bonding and intramolecular hydrogen bonding.
The molecule must contain a highly electronegative atom connected to the hydrogen atom.
The electronegative atom should have a small size. A smaller size enhances electrostatic attraction.

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