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Hydrogen Bond

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Last updated date: 19th Apr 2024
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What is a Hydrogen Bond?

A hydrogen bond is a kind of bonding that is present between an atom of hydrogen and a pair of other atoms having a high electronegativity. Hydrogen-bonding used to be competitively weaker than ionic bonding or covalent bonding, but it is stronger than van der Waals forces. Hydrogen bonding can exist in two ways. One is that it can occur between atoms of different molecules or in the atoms of the same molecule.

And another one in which atom of the pair, which is also known as donor as it donated electrons  ( mostly fluorine (F), nitrogen (N), or oxygen (O) atom), is covalently bonded to a hydrogen atom (-FH, -NH, -OH). Its high electron affinity makes the hydrogen atom take on a slight positive charge. The other pairs of atoms, i.e. F, N, or O, contain an electron pair that is not shared, which provides it with a slight negative charge. To form a bond the donor atom effectively shares its hydrogen with the acceptor atom mainly through electrostatic attraction. 


Types of Hydrogen Bonding

There are two types of hydrogen bondings which are given below.

  1. Intramolecular Hydrogen Bonding

  2. Intermolecular Hydrogen Bonding

Now understand each type of hydrogen bonding in detail.

1. Intramolecular Hydrogen Bonding

Within a single molecule, an intramolecular hydrogen bond is formed. It is formed when two functional groups of a molecule form hydrogen bonds with each other. In order to form intramolecular hydrogen bonding, the hydrogen donor and hydrogen acceptor must be present within one molecule. They must be present within each other’s proximity.

Examples Intramolecular Hydrogen Bonding - 

  • Ethylene glycol (C₂H₄(OH)₂) has two hydroxyls groups. Here hydrogen bonding is present between the two groups due to molecular geometry.

  • One more example of a molecule that shows this type of hydrogen bonding is salicylaldehyde(C₇H₆O₂).


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2. Intermolecular Hydrogen Bond

An intermolecular hydrogen bond is formed between two or more separate molecules in a substance. The donor atoms and acceptor atoms that took part in hydrogen are present in suitable positions where they can interact. 

Examples of Intermolecular Hydrogen Bond - Some Examples of Intermolecular Bonds of Hydrogen Bonds are given below.

  • Water (H₂O)

  • Ethanol (C₂H₅OH)

  • Ammonia (NH₃)

  • Hydrogen fluoride (HF)


Properties of Hydrogen Bonding

Some of the properties of hydrogen bonding are given below.

  • It is a weak force of attraction between molecules.

  • Any compound or molecule having hydrogen bonding shows different physical properties. For example, if hydrogen bonding is present, it increases the melting and boiling point of a substance. As a result of this, it makes it less volatile.

  • It is stronger than the weak Van der Waals bonds.

  • Hydrogen bonds are comparatively weaker than covalent and ionic bonds.


Hydrogen Bonding Examples

Some examples of hydrogen bonding are as follows.

1. Water

A water molecule is composed of a highly electronegative oxygen atom linked to the hydrogen atom. The electrons of the shared pair are attracted more by the oxygen atom, and this end of the molecule becomes negative, and the hydrogen atoms become positive.


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2. Ammonia

The hydrogen bonds in ammonia (NH3) are formed between nitrogen and hydrogen atoms. Nitrogen is a highly electronegative atom that is linked to hydrogen atoms in order to make hydrogen bonds.


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3. Hydrogen Fluoride

Fluorine is an element that has the highest value of electronegativity, and it forms the strongest hydrogen bond.


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4. Alcohols

Alcohols are organic compounds. It contains at least one -OH group. When any molecule containing the hydrogen atom is connected to either oxygen or nitrogen directly, it usually has the tendency to form hydrogen bonding.


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5. Carboxylic Acid

Hydrogen bonding can occur in a pure carboxylic acid in between two molecules of acid in order to produce a dimer. The hydrogen bonding in carboxylic acid doubles the size of the molecule.


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Applications of Hydrogen Bonding

In different types of chemical and biological processes, hydrogen bonding is necessary. Some of the applications and effects of hydrogen bonds are given below. 

  • Hydrogen Bonds in Plants

Water has the property to stick to itself (cohesion) and also with other molecules (adhesion). When water droplets fall on a leaf, the hydrogen bonds present between the molecules of water are more substantial than the intermolecular forces of adhesion between the water molecules and the leaf. The high surface tension of water is explained by this property.

  • Hydrogen Bonds in Proteins

Intramolecular hydrogen bonding is responsible for different types of proteins such as secondary proteins, tertiary proteins, and quaternary proteins and as well as for the structure of the nucleic acids.

  • Hydrogen Bonds in DNA (Deoxyribonucleic Acid)

The double-helix model of DNA consists of two intertwined strands held together by a base pair. The hydrogen bonding present between the bases on adjacent strands is responsible for this. Because of different structure bases, adenine (A) always forms hydrogen bonds with thymine (T). Guanine (G) always forms hydrogen bonds with cytosine (C) in contrast.


Do you know?

Fluorine (F) is the most electronegative element having a value of electronegativity of 3.98. The hydrogen bond is strongest in Fluorine. 


Conclusion 

A hydrogen bond is a type of chemical bonding that is formed because of the electrostatic attraction between a hydrogen atom and an atom containing a lone pair of electrons in a substance. We get important information related to hydrogen bonding, such as hydrogen bonding examples, properties and effects of hydrogen bonds etc.

FAQs on Hydrogen Bond

1. How is Hydrogen Bond Formed?

The formation of hydrogen bonding occurs when a hydrogen atom is bonded to an electronegative atom. The shared pair of electrons is attracted to the electronegative atom when a hydrogen atom is covalently bonded to an electronegative atom. As a result of this, the hydrogen atom gains a slightly positive charge and the electronegative atom gains a slightly negative charge. This property of having a slight charge is called polarity, and such molecules are called polar molecules. When two or more of this type of molecule are present in a substance, the positive end of one molecule is attracted to the opposing end of the other molecule. Thus a hydrogen bond is formed.

2. Why do compounds containing hydrogen bonds have high melting and boiling points?

The compounds that contain hydrogen bonds show abnormally high melting and boiling points in comparison to the compounds that do not contain hydrogen bonds. The compounds having hydrogen bonds contain high boiling as well as melting points because some extra energy is required to break these bonds. They are bonded with more attraction so more energy will be needed. Hydrogen bonding in water causes linkages in the water molecules which result in the boiling point of water being more than that of the other compounds. Ammonia (NH₃) has a higher boiling point than PH3 because there is hydrogen bonding in NH₃ but not in PH₃. Ethanol is an organic compound that has a higher boiling point than diethyl ether because there is hydrogen bonding in ethanol.