Structure, Molecular Geometry, and Hybridization of H2O

H2O is the molecular formula of water, which is one of the most abundant substances on Earth. The covalent bond holds together two hydrogen atoms and one oxygen atom to form a single molecule. In addition, two or more H2O molecules combine via hydrogen bonds to form a compound.

Covalent bonds are stronger than hydrogen bonds, which explains why water quickly reacts with the vast majority of elements in the periodic table.

Lewis structure, also known as an electron dot structure, is a graphical representation of determining the total amount of valence electrons present in an atom, which are available to undergo bond formation to create a molecule and, ultimately, a compound.

The valence electrons are depicted as dots surrounding the atom symbol, typically in pairs.

According to the octet rule, the maximum number of dots that can be painted per atom is eight. Moreover, the lines illustrate the development of a bond as a result of valence electrons reacting.

Hydrogen atoms have an electrical configuration of 1s1 due to their atomic number of one. Due to the fact that the 1s shell can only hold a maximum of two electrons, there is a deficiency of one electron.

One valence electron is added to a single hydrogen atom.

In addition, the electronic arrangement of oxygen is 1s2 2s2 2p4, where the 2p shell may hold six electrons.

Due to the deficiency of two electrons, an oxygen atom has six valence electrons in total.

What do valence electrons consist of?

The valence electrons are “free electrons” found in the atom’s outermost shell. The nucleus holds the outer shell tenuously because it is the most distant.

In addition, if the valence electrons are unpaired, they become extremely reactive by receiving or giving electrons to stabilise the outermost shell.

It is fascinating to consider that the greater the quantity of valence electrons, the greater the ability to receive electrons.

As the quantity of valence electrons decreases, the atom’s ability to give electrons will increase.

What exactly is the Octet rule?

According to the Octet rule, an atom can have a maximum of eight valence electrons. In addition, these eight electrons are only depicted surrounding the atom symbol in the Lewis structure.

Oxygen is lacking in two valence electrons. In contrast, the two hydrogen atoms lack a total of two valence electrons.

The Lewis structure of H2O is depicted such that each atom’s deficiency is satisfied.

H2O’s Lewis Structure

The Lewis structure of hydrogen and two oxygen atoms reveals that a total of eight valence electrons contribute to the creation of the H2O molecule.

Here, we must comprehend how the Lewis structure for the H2O molecule is drawn:

Check the total number of valence electrons: It takes eight H2O molecules to make one.

Consider the number of electrons required: The octet rule states that there are four water (H2O) molecules for every one octet.

Determine the number of single covalent bonds forming between each oxygen and hydrogen atom.

Select a core atom: The Oxygen atom will serve as the primary atom.

Create a Lewis diagram:

The Molecular Geometrical Structure of H2O

The binding angle between hydrogen, oxygen, and hydrogen atoms is 104.5°. This demonstrates that the geometrical structure of a single H2O molecule is curved.

The Valence Shell Electron Pair Repulsion (VSEPR) theory explains why the bond angle is lowered to 104.5° regardless of the presence of two pairs of lone electrons on the oxygen atom.

The optimal bond angle for a molecule with a bent form is 109.5 degrees.

According to the Lewis structure, a lone pair exists when none of the valence electrons surrounding an atom are paired.

Similar is the case with the oxygen atom in the H2O molecule, which contains two lone pairs.

These lone pairs distort the bond angle due to the repulsion between lone pairs, which is greater than the repulsion between bond pairs and lone pairs.

The bond angle decreases as the number of lone pairs increases. Due to the presence of two lone pairs on the oxygen atom, the bond angle is reduced to 104.5°.

Combining of H2O molecules

There are no pi () links between oxygen and hydrogen atoms in a water molecule; only sigma () bonds exist.

Sigma () bonds are the strongest covalent bonds, as is well known. Consequently, there is a high degree of stability between the oxygen and hydrogen atoms.

It is the oxygen atom’s two lone pairs that make all the difference. The oxygen of a water (H2O) molecule is hybridised in the sp3 configuration.

The single oxygen atom in the water (H2O) molecule has one 2s orbital and three 2p orbitals, as seen by the diagram. The combination of these four results in the production of four sp3 hybridised orbitals.

It results in the creation of the tetrahedral bent geometry, where the entire H2O molecule displays 25% s features and 75% p characteristics.

It can be further elucidated with the aid of an H2O molecule molecular orbital diagram.

The 2s orbital and three 2p orbitals of the oxygen atom combine to generate four new hybrid orbitals that further bond with the 1s orbital of the hydrogen atoms through overlapping.

Water Molecular orbital diagram (H2O)

The molecular orbital diagram is a graphical representation of the process of determining chemical bonding between molecules of a substance.

In addition, the molecular orbital diagram aids in estimating the formation of two sigma bonds and the effect of lone pairs on the structure.

The six valence electrons are bonding with the 1s orbital electrons of the hydrogen atom, as seen in the diagram.

Mixing and overlap are occuring between atomic orbitals with similar energy.

Higher-energy antibonding molecular orbitals are being formed by bonding electrons with lower energies.

Due to the paucity of electrons, the left oxygen electrons do not overlap further.

The electronegativity of oxygen is higher than that of hydrogen. As a result, oxygen has a greater negative charge than hydrogen, which has a positive charge. It causes oxygen to grab adjacent electrons and finally form a bond.

Hydrogen, on the other hand, does not react with adjacent molecules because it has already completed its orbital and formed a strong sigma bond with oxygen.

It results in the development of polarity in an H2O molecule, regardless of the molecule’s net neutral charge.

Additionally, you can read an intriguing article regarding the polarity of water.

Conclusion

There are two single sigma bonds between the oxygen atom and the hydrogen atoms in the Lewis structure of the triatomic H2O molecule. In addition, these connections leave two lone pairs of electrons on the oxygen atom, which significantly contribute to the tetrahedral bent geometry of the H2O molecule.

It is the reason why the bond angle, which ought to be 109.5°, is really 104.5°. Four hybrid orbitals are formed when one s orbital and three p orbitals combine to generate sp3 hybridization in the H2O molecule.

Read more: Polar or nonpolar is SF4?

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.

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