A Hydrogen Bond
A hydrogen bond is an electromagnetic attraction produced in between a partially positively charged hydrogen atom attached to a highly electronegative atom and another nearby electronegative atom.
A hydrogen bond is a kind of dipole-dipole interaction; it is not a true chemical bond. These attractions can occur between molecules (intermolecularly) or within various parts of a single molecule (intramolecularly).
Formation of Hydrogen Bond
In molecules consisting of N-H, O-H, or F-H bonds, the big difference in electronegativity between the H atom and the N, O or F atom leads to a highly polar covalent bond (i.e., a bond dipole).
Because of the distinction in electronegativity, the H atom bears a large partial positive charge and the N, O, or F atom bears a high partial negative charge. Thus, partially different charges bring in each other, and a hydrogen bond is formed.
Hydrogen Bond Donor
A hydrogen atom attached to a fairly electronegative atom is a hydrogen bond donor. This electronegative atom is typically fluorine, oxygen, or nitrogen. The electronegative atom attracts the electron cloud from the hydrogen nucleus and, by decentralizing the cloud, leaves the hydrogen atom with a positive partial charge.
Because of the small size of hydrogen relative to other atoms and molecules, the resulting charge, though only partial, is stronger. In the molecule of ethanol, there is one hydrogen atom bonded to an oxygen atom, which is very electronegative. This hydrogen atom is a hydrogen bond donor.
Hydrogen Bond Acceptor
A hydrogen bond results when this strong partial positive charge draws in a lone pair of electrons from another atom, which ends up being the hydrogen bond acceptor. An electronegative atom such as fluorine, oxygen, or nitrogen is a hydrogen bond acceptor, no matter whether it is bonded to a hydrogen atom or not.
Greater electronegativity of the hydrogen bond acceptor will develop a more powerful hydrogen bond. The diethyl ether molecule includes an oxygen atom that is not bonded to a hydrogen atom, making it a hydrogen bond acceptor.
Strength of the Hydrogen bond
The hydrogen bond is a weak bond. The strength of the hydrogen bond is in-between the weak van der Waals forces and the strong covalent bonds.
The dissociation energy of the hydrogen bond depends upon the attraction of the shared pair of electrons and for this reason on the electronegativity of the atom.
Examples of Hydrogen Bonding
Hydrogen Bonding in Hydrogen fluoride
Fluorine having the greatest value of electronegativity forms the strongest hydrogen bond.
Hydrogen Bonding in Water
A water molecule contains a highly electronegative oxygen atom linked to the hydrogen atom. Oxygen atom draws in the shared pair of electrons more and this end of the molecule becomes negative whereas the hydrogen atoms end up being positive.
Hydrogen Bonding in Ammonia
It consists of highly electronegative atom nitrogen linked to hydrogen atoms.
Hydrogen Bond in Alcohols and Carboxylic acid
Alcohol is a kind of organic molecule which includes an -OH group. Usually, if any molecule which includes the hydrogen atom is connected to either oxygen or nitrogen directly, then hydrogen bonding is quickly formed.
Properties of Hydrogen Bonding
- Solubility: Lower alcohols are soluble in water because of the hydrogen bonding which can take place between water and alcohol molecule.
- Volatility: As the compounds including hydrogen bonding in between various particles have a greater boiling point, so they are less unstable.
- Viscosity and surface area tension: The substances which consist of hydrogen bonding exists as an associated molecule. So, their circulation ends up being comparatively difficult. They have higher viscosity and high surface tension.
Applications for Hydrogen Bonds
- Hydrogen bonds take place in inorganic molecules, such as water, and organic molecules, such as DNA and proteins. The two complementary strands of DNA are held together by hydrogen bonds in between complementary nucleotides (A&T, C&G). Hydrogen bonding in the water adds to its unique properties, including its high boiling point (100 ° C) and surface area tension.
- The hydrogen bonds formed in between water molecules in water drops are more powerful than the other intermolecular forces between the water molecules and the leaf, contributing to high surface area tension and unique water drops.
- In biology, intramolecular hydrogen bonding is partly responsible for the secondary, tertiary, and quaternary structures of proteins and nucleic acids. The hydrogen bonds help the proteins and nucleic acids form and keep specific shapes.
Summary
There exist some attractive forces which bind different atoms or elements together to form molecules or compounds. Hydrogen bonding is one of them. When partially positively charged hydrogen attached to a highly electronegative atom, the bond that will form is called hydrogen bond. Hydrogen bond is the part of compound and molecules which are vital for life. DNA bases are attached to each other by hydrogen bond. Hydrogen bonding in water makes it unique by adding properties like its boiling point at 100 ° C and surface area tension. Hydrogen bonding is also responsible for secondary, tertiary and quaternary structure of proteins.