Hydrogen Bonding

Hydrogen bonding refers to the formation of Hydrogen bonds, which are a special category of attractive intermolecular forces arising from the dipole-dipole interaction between a hydrogen atom bonded with a very strong electronegative atom and another very strong atom at -electronegative nearby. a hydrogen atom. For example, in water molecules (H2O), hydrogen is bound together by an electronegative oxygen atom. Thus, hydrogen bonding arises from water molecules due to the dipole-dipole interaction between the hydrogen atom of a water molecule and the oxygen atom of another H2O molecule.

Here, the location of bond electrons in the O-H bond is very close to the oxygen nucleus (due to large differences in the electronegativities of oxygen and hydrogen). Therefore, the oxygen atom enhances the negative charge partially (-δ) and the hydrogen atom promotes a partially positive charge (+ δ). Now, hydrogen bonding is possible due to the electrostatic attraction between the hydrogen atom of one water molecule (with charge + δ) and the oxygen atom of another water molecule (with charge δ). Therefore, hydrogen bonds are a very special category of intermolecular gravitational forces that occur only in computers with hydrogen atoms combined with a very strong electronegative atom. Hydrogen bonds are much stronger compared to normal dipole-dipole forces and dispersion forces. However, they are weak compared to real covalent or ionic bonds.

What are the Terms of Hydrogen Bonding?

In a molecule, when a hydrogen atom is attached to a very strong electronegative atom, it pulls a combined pair of electrons over and so this end of the molecule becomes slightly worse while the other end is slightly positive. The wrong end of one molecule leads to a better ending for another and as a result, a weak bond is formed between them. This bond is called a hydrogen bond.

As a result of hydrogen bonding, a hydrogen atom binds two electronegative atoms simultaneously, one by a covalent bond and the other by a hydrogen bond. The conditions for hydrogen binding are:

• A molecule must have a very strong electronegative atom attached to a hydrogen atom. The higher the electronegativity the more molecular separation.

• Carboxylic acid molecules exist as a dimer due to hydrogen bonding. The cell groups of such compounds are found to be twice as large as those calculated in their simplest form.

Separation

In an aqueous solution, HF separates and delivers difluoride ions instead of fluoride ions. This is due to the interaction of hydrogen in HF. The molecules of HCl, HBr, HI do not form a hydrogen bond. This explains the absence of compounds such as KHCl₂, KHBr₂, KHI₂.

Why do Compounds with Hydrogen Bonding have High Melting and Boiling Points?

Compounds with hydrogen bonding show unusually high melting points and boiling points. The high point of melting and boiling of compounds containing hydrogen bonds is due to the fact that more energy is needed to break these bonds.

The unusually high boiling point of hydrogen fluoride between halogen acids is due to the presence of hydrogen bonding.

H₂O is a liquid while H₂S, H₂Se and H₂Te are all standardised gases. In water, hydrogen bonding creates a contact in water molecules which results in the boiling point of water being higher than in other compounds.

Ammonia has a higher boiling point than PH₃ because there is a hydrogen bond in NH₃ but not in PH₃.

Ethanol has a higher boiling point than diethyl ether because it has hydrogen bonding in ethanol.

Examples of Hydrogen Bonding

• Hydrogen Bonding on Hydrogen fluoride: Fluorine with a very high degree of electronegativity forms a very strong hydrogen bond.

• Hydrogen Bonding in Water: A water molecule contains the strongest oxygen atom attached to a hydrogen atom. The oxygen atom pulls a combined pair of electrons over and this end of the molecule becomes negative while the hydrogen atoms become positive.

• Hydrogen Bonding in Ammonia: It contains the strongest atomic nitrogen attached to hydrogen atoms.

• Hydrogen Bonding to Alcohols and Carboxylic acid: Alcohol is a type of living molecule that contains the group -OH. Generally, if any molecule containing a hydrogen atom is directly connected with oxygen or nitrogen, then hydrogen bonding is easily formed.

• Hydrogen Bonding to Polymers: Hydrogen synthesis is an important factor in determining the 3D structures and structures obtained by synthetic and natural proteins. Hydrogen bonds also play an important role in defining cellulose composition and polymers found in cotton or flax.

• Hydrogen bond strength: The hydrogen bond is a weak bond. Hydrogen bond strength is between van der Waals strength and strong covalent bonds.

The separating force of a hydrogen bond depends on a pair of shared electrons and therefore on the electronegativity of the atom.

Hydrogen Bonding Structures

• Solubility: Low alcohol dissolves in water due to possible hydrogen bonding between water and alcohol molecules.

• Volatility: As compounds that combine hydrogen bonding between different molecules have a high boiling point, so they do not change slightly.

• Viscosity and surface tension: Materials containing hydrogen bonding exist as a related molecule. So their travels are relatively difficult. They have high viscosity and high surface area.

• Low water congestion with water: In the case of solid ice, hydrogen bonding causes a cage-like formation.