Hybridisation of Water Molecules

Water is an inorganic compound with a polar molecule. At room temperature, it is a colourless and odourless liquid. More studies have been conducted on water than on any other compound. It is known as the universal solvent and even the solvent of life. All these properties of water are a result of its molecular structure. Water is the most abundant compound on the surface of the Earth along with being the third-most abundant molecule after molecular hydrogen and carbon monoxide.

Bonding in water molecules

The molecules of water form hydrogen bonds with each other because of the polar nature of the molecules. The polar nature is a result of the molecular geometry of water. This polarity of the molecules makes ions in salts dissociate, and it also causes bonds to form with acids and alcohol. Hence, water is known as a universal solvent. This hydrogen bonding results in the many unique characteristics of water.

Characteristics of water caused due to hydrogen bonding

●  The solid form of water is less dense than the liquid form.

●  Its boiling point of 100 degrees Celsius is relatively high for its molar mass.

●  It attains a high heat capacity.

Molecular structure of the water molecule

The water molecule is polar. This is because the two lone pairs of electrons left in oxygen after forming bonds with hydrogen atoms push the orbitals, making the water molecule achieve a non-linear, bent shape.

Hybridisation of water molecules

Molecules that have more than two atoms bonding together for their formation require a more complex model than those that are formed by two atoms. The water molecule is one such example of multiple atoms coming together to form a molecule. 

The water molecule is made up of one oxygen atom and two hydrogen atoms. The electronic configuration of oxygen is 1s22s22p4.  Each of the two 2p orbitals has a pair of unpaired electrons. If the valence bond theory was used to determine the molecular geometry, it would suggest that the O-H bond would form by the overlapping of the 2p orbital of oxygen with the 1s orbital of hydrogen. This would result in the bond angle being 90 degrees. 

However, it has been determined by conducting experiments that the bond between oxygen and hydrogen is 104.5 degrees. This difference in result is explained by quantum mechanical calculations.

There is a mathematical rule called the wave function. This wave function describes the wave-like nature of electrons. When atoms combine, this wave function produces different shapes of orbitals. This combination of the wave functions of atomic orbitals is called hybridisation. The orbitals that are formed as a result of hybridisation are called hybrid orbitals.

An isolated oxygen atom has one 2s orbital and three 2p orbitals in the valence orbitals. But when an oxygen atom combines with hydrogen atoms in a water molecule, the valence orbital differs. In this situation, the valence orbitals of oxygen become four hybrid orbitals, with each orbital pointing towards the corners of a hypothetical tetrahedron.

Characteristics of hybridisation

There are certain characteristics and conditions necessary for the hybridisation of a molecular orbital. These are as follows:

●  Hybrid orbitals form when covalent bonding occurs. They cannot occur in isolated atoms.

●  The shapes and orientations of hybrid orbitals differ from those orbitals that are found in isolated atoms.

●  Hybrid orbitals are a result of the combination of atomic orbitals. So the total number of hybrid orbitals can be obtained by counting the number of combined atomic orbitals.

●  All the hybrid orbitals belonging to a particular set have the same shape and energy.

●  The electron pair geometry of a molecule is the deciding factor in what type of hybrid orbital formation will take place.

●  The hybrid orbitals overlap and form sigma bonds with each other.

Conclusion

The hybridisation of water is the result of the combination of the wave functions of the valence orbitals of oxygen and hydrogen. The reason why the orientation of the orbitals is not linear as predicted by the valence bond theory is because the lone pairs of electrons in the oxygen atom of a water molecule push the orbitals from their linear orientations. The hybridisation of water molecules makes them have many unique properties that are vital to maintaining life on Earth.