High Melting and Boiling Points of Compounds

The first element in the periodic table is hydrogen. Under normal circumstances, it is an odourless, tasteless, and colourless gas. Hydrogen bonding is the process of creating hydrogen (H) bonds, which is an intermolecular attractive force that results from the interaction of a hydrogen atom with a strongly electro-negative atom. Hydrogen shows covalent bonds to the electronegative atom in H2 molecules, which are chemically represented as (H2O). Due to the dipole-dipole interactions between oxygen and hydrogen atoms, hydrogen bonding increases in water molecules.

What do you mean by hydrogen bonding?

Hydrogen bonding refers to the formation of hydrogen (H) bonds which is an intermolecular attractive force induced by the dipole-dipole interaction between hydrogen atoms and strongly electronegative atoms. The hydrogen bond is often weaker than the covalent or ionic link. It is, however, more powerful than the Van der Waals forces. Hydrogen bonds are a form of a weak chemical link, according to experts. The hydrogen bond is further classified into two types:

Intermolecular hydrogen bonding: Intermolecular hydrogen bonding can be defined as when the hydrogen bonding takes place between different molecules that have either the same or other compounds. The most common examples are hydrogen bonding in alcohol, water, and ammonia. 

Intramolecular hydrogen bonding: Intramolecular hydrogen bonding can be defined as hydrogen bonding that takes place within the molecule only. It mainly occurs in compounds that have two groups.

Why Do Compounds Having Hydrogen Bonding Have High Melting and Boiling Points?

• The melting and boiling temperatures of hydrogen-bonded compounds are unusually high. The high boiling and melting points of hydrogen-bonded compounds are due to the additional energy required to scatter these bonds.
• Hydrogen bonding accounts for hydrogen fluoride’s particularly higher boiling point among halogen acids.
• At room temperature, H2O is a liquid, whereas H2S, H2Se, and H2Te are gases. Hydrogen bonding produces links in H2O molecules, resulting in water having a higher boiling point than the other chemicals.
• Due to the hydrogen bonding in NH3, but not in PH3, ammonia has a higher boiling point than PH3.
• As ethanol contains hydrogen bonds, it has a higher boiling point than diethyl ether.

Hydrogen Bonding Conditions

The shared piece of an electron is attracted in the molecule when the hydrogen atom is closely coupled to the highly electronegative atom. As a result, one end of the molecule becomes slightly negative, while the other becomes slightly positive. Both ends are attracted to one another, resulting in the creation of a weak bond. The hydrogen bond is the name for this type of bond. There are two major hydrogen bonding conditions:

A highly electronegative atom should be connected to the hydrogen atom in each molecule. The stronger the electronegativity, the higher the polarisation of the molecule.

The size of the electronegative atom should be tiny. The electrostatic attraction will be stronger if the size is smaller.

Examples of Hydrogen Bonding

Water – It is a great example of hydrogen bonding in action. The link is formed between one water molecule’s hydrogen and the oxygen atoms of some other water molecule, not between two hydrogen atoms. The highly electronegative oxygen atom gets connected with the hydrogen atom in a water molecule. The electron’s shared pairs are closely attracted to the atoms of oxygen which is why the molecule’s end becomes negative whereas the hydrogen atoms appear to be positive.

Chloroform: In chloroform, hydrogen makes a bond between one molecule of hydrogen and another molecule of carbon.

Hydrogen fluoride – In hydrogen bonding, fluorine forms the strongest hydrogen bond featuring the highest electronegativity.

Hydrogen bonding in carboxylic acid and alcohols – Alcohol is referred to as an organic molecule with an -OH group. Generally, in case any molecule that has a hydrogen atom is either linked to nitrogen or oxygen directly; later, hydrogen bonding becomes easier.

Hydrogen bonding in the ammonia – It has electronegative atom nitrogen connected to hydrogen atoms.

Hydrogen bonding in the polymer – In order to determine 3D structures and properties which are acquired by natural and synthetic proteins, hydrogen bonding is a crucial factor. It also plays a significant role in defining the cellulose structure along with derived polymers, including flax or cotton.

Conclusion

In the above article, we have read about hydrogen bonding and the reason behind the high melting and boiling points of the hydrogen components. Hydrogen bonding is the development of hydrogen (H) bonds that is an intermolecular attractive force caused by the dipole-dipole interaction between a hydrogen atom bound to a strong electro-negative atom and another very electronegative atom nearby.