Definition of hydrogen bonding in chemistry
The hydrogen bond is a very unstable bond where the hydrogen atom participating in bonding with high electronegativity atom. Thus H-bonding formes between hydrogen and fluorine, oxygen, nitrogen, and less extent of chlorine and sulfur atom.
But positive hydrogen end can link some specific negative dipole end present in another or same molecule. Thus there effectively forming a weak bond to the second electronegative atom. This weak secondary bond is known as the H-bond.
Thus hydrogen bond is an unstable bond uses to explain the unexpected properties of inorganic and organic hydrocarbons.
Types of H-bonding with examples
Bonding formation involving one molecule only or between two or more molecules hydrogen bond are two types.
Examples of intermolecular hydrogen bond
Intermolecular H-bonding formed between two or more molecules which give rise to the association.
The general expected trend of increasing boiling points and the melting points of binary hydride can explain by intermolecular H-bonding. Thus with the increasing atomic number along with a group boiling points also increases.
But ammonia in group 15 water in the group 16 and hydrogen fluoride in group 17 violated these trends. This abnormal trends can explain due to the association of the molecule by H-bonding.
Hydrogen bonding in water
The water molecule can form a covalent bond between hydrogen with the oxygen atom. But due to the high electronegativity of oxygen, hydrogen developed a positive polarity.
Thus positive poles of water molecules drag the negative end of a second water molecule and so on. This result is an association of molecules of water to form a liquid.
Hydrogen bonding in ice
X-ray crystallographic study of crystalline ice revels that each oxygen atom of the water molecule tetrahedrally surrounded by four other oxygen atoms. Each oxygen pair has in between them a hydrogen atom and the structure extended in all directions in space.
But due to hydrogen bonding there exist a huge number of holes in ice structure. With this form of structure and hydrogen bond, we can explain why ice has a lower density than the water molecule.
Examples of intramolecular hydrogen bond
Intramolecular H-bonding involving one molecule only. Hence it gives rise to ring formation or chelation. Thus o-hydroxybenzaldehyde and o-nitrophenol have their hydrogen bond restricted within the same molecules. Such bonding compares the boiling point in nitrophenol molecules.
Hydrogen bond in ortho nitrophenol
o-nitrophenol has hydrogen bonding limited within the same molecule but p- and m-nitrophenol extends to the neighboring molecules. Thus p- and meta nitrophenol gathering a large number of the molecule through the H-bond.
o-hydroxy benzaldehyde also restricted H-bonding within the molecule. Thus this leads to weakening acid properties of the compound. Due to H-bonding, there is limited scope for the formation of hydrogen ion in the solution.
Biological importance of hydrogen bonding in water
In chemical and biological science, the importance of hydrogen bonding is very important for the existence in our environment. Because of the absence of hydrogen bonding in water would be a gas phase at ordinary temperature.
Without liquid water, we can not imagine the existence of an animal or vegetable life. Thus there we can not imagine our environment with no animal or vegetable life.