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A hydrogen bond, also expressed as an H-bond, can be defined as the electrostatic bond of a hydrogen atom with a covalent bond of another electronegative group of elements or atoms.
Electrostatic force can be explained as the force generated between two objects (in the case of a hydrogen bond- between two atomic particles) due to electric charges, which makes the two bodies attracted towards each other.
A covalent bond can be explained as a chemical bond between two atomic particles, which is created due to sharing of electron pairs between the two respective atomic particles. A covalent atomic bond is also referred to as bonding pairs or shared pairs.
Hydrogen bond definition
A hydrogen bond can be explained as a weak bond created between a hydrogen atom and an electronegative element that has a lone pair to share with the hydrogen atom to create an electrostatic attraction between portions of the molecule of the two atoms.
The nature of a hydrogen bond is either dipole-dipole type, ion-dipole type, or dipole-induced dipole type.
The hydrogen atom forms a bond with mainly the chemical elements of fluorine, nitrogen, and oxygen. In the context of organic chemistry, it forms a bond with the elements of carbon and chlorine.
There are certain prerequisites for forming a hydrogen bond, such as the element forming a bond with the hydrogen atom must be electronegative. Also, the atom’s electronegativity must be equal to or greater than 3. And finally, the atom must have a lone pair to share with the hydrogen atom, which must be smaller in size.
The elements which form a bond with hydrogen have the following electronegative charge:
Fluorine -4.0
Oxygen -3.5
Nitrogen -3
Chlorine -3 (the study of the formation of a hydrogen bond between the hydrogen atom and the atom of chlorine is known as organic chemistry)
Features of hydrogen bonding:
Hydrogen bonding occurs when the molecules of an element that contains atoms exert a greater pull on the covalent bond formed by the hydrogen atom resulting in the shared electrons orbiting the hydrogen atom more than the atom they are bonded to (referring to the covalent bond here).
A hydrogen bond is a weaker form of the bond than the covalent bond formed by the hydrogen atom and another element.
A hydrogen bond is comparatively stronger than a simple dipole-to-dipole bond but weaker than an ionic bond.
Hydrogen bonding occurs due to the attraction of two or more electrically charged molecules, which have a small electric charge known as a dipole, which translates to “two poles”.
As you will see in the further sections of this article, one of the molecular poles is negative, whereas the other is positive.
The electromagnetic forces between one section of the molecules are felt by the electrically charged molecules of the other section of the bonding.
Hydrogen bonding
Hydrogen bonding is explained as the intermolecular forces between polar molecules. Hydrogen bonding is a special type of dipole force between highly polarized molecules.
The chemical elements which usually form a bond with the hydrogen atom are fluorine, nitrogen, and oxygen. And in certain organic chemical cases, the hydrogen atom also forms a chemical bond with carbon and chlorine (this falls under the umbrella of organic chemistry).
For example- hydrogen bonding is intermolecular forces between polar molecules of water, hydrogen bonding exists in ammonia molecules, and hydrogen bonding exists in hydrogen fluoride molecules.
Hydrogen bonds are usually weaker than ionic and covalent bonds, but it is also important to note that hydrogen bonds are stronger than Van der Waal Force.
The atomic energy between these types of bonds are as follows:
Vander Waal bond energy: 8KJ/mole
Ionic and covalent bond energy: 200 KJ/mole
Hydrogen bond energy: 8-42 KJ/mole
Hydrogen bonding can be explained through the following example:
A𝜹- H𝛿+ :B
Explanation of the above diagram:
Here we have taken the example of an atom -A, which is electronegative.
We also have a Hydrogen atom in the example, which is electropositive in all cases.
Since the atoms have opposite polar attractions, they are attracted to each other, i.e., and the hydrogen atom is attracted to the atom -A.
Now, we take an example of an atom -B, which has a lone pair and is in the hydrogen atom’s proximity.
The atom -B would now want to share its electrons with the hydrogen atom. This example of sharing electrons between atom- B and the hydrogen atom is known as a hydrogen bond.
The previous example of attraction between the hydrogen atom and the atom -A is known as a covalent bond.
The condition for forming a covalent bond with the hydrogen atom for any chemical element is that the electronegativity of that element must be greater than or equal to 3.
The conditions for the formation of a hydrogen bond with atom- B are as follows:
Atom B must be electronegative
The atom must be of a smaller size
The atom must have a lone pair
The bond energy in the covalent bond between the hydrogen atom and the atom -A is 200 KJ/mole.
The bond energy in the hydrogen bond between the hydrogen atom and the atom -B is 8-42 KJ/mol.
Hence, it can be concluded that the bond energy in the covalent bond, i.e., between the atom -A and hydrogen atom, is much greater than the bond energy in the hydrogen bond created between the hydrogen atom and atom- B.
Intramolecular hydrogen bonding
The intra-molecular forces can be defined as the bonding forces within a molecule. The word “intra” means “within”. Hence, intra-molecular forces exist within a molecule. For example- intra-molecular forces exist in a molecule of water.
Intramolecular hydrogen bonding, also termed chelation bonding, is formed within a molecule. For example, in salicylic acid, hydrogen is attached to one oxygen with a covalent bond and an intramolecular hydrogen bond.
Intermolecular hydrogen bonding is formed between two or more different molecules of the same or different types. For example, HF, H2O, NH3, R-OH, R-COOH.
Conclusion
A hydrogen bond can be defined as an electrostatic force between a hydrogen atom and another chemical element which leads to sharing of electrons (lone pairs) between the two atoms.
The first and foremost criterion for forming a hydrogen bond is that the atom must be of a smaller size. Hence, hydrogen generally forms a bond with fluorine, oxygen, and nitrogen. And in the context of organic chemistry, hydrogen forms a bond with chlorine and carbon.
The chemical elements which usually form a bond with the hydrogen atom are fluorine, nitrogen and oxygen. And in certain organic chemical cases, the hydrogen atom also forms a chemical bond with carbon and chlorine (this falls under the umbrella of organic chemistry).
There are also the following criteria that are to be fulfilled for the hydrogen to form a bond:
The atom must be electronegative
The atom must be smaller in size
The atom must have a lone pair
