Water, one of the Earth’s major constituents, has the molecular formula H2O. A molecule of water is made up of two hydrogen atoms and one oxygen atom that are joined together by a covalent bond. Furthermore, two or more H2O molecules join together by hydrogen bonds to form a compound.
The Lewis structure, also known as an electron dot structure, is a diagrammatic representation of determining the total number of valence electrons present in an atom that are ready to form bonds to form a molecule and, eventually, a compound.
Table of Contents
- How to draw Lewis Structure for H2O
- Molecular Geometry of H2O
- Hybridization of H2O
- Polarity of H2O
- Frequently Asked Questions – FAQs
How to draw Lewis Structure for H2O
Below given steps are to be followed while drawing the Lewis structure for H2O-
1. Determine the total number of electrons in the valence shells of hydrogen and oxygen atoms.
In the periodic table-
Hydrogen is a Group IA element with one electron in its outermost shell (valence shell).
Oxygen is a Group VIA element with six electrons in its last shell.
Therefore, the total number of valence electrons required to draw the lewis structure of H2O= 1(2)+6 = 8 valence electrons.
2. Determine the total electron pairs in the form of lone pairs and bonds.
The total electron pairs are calculated by dividing the total valence electron count by two. In the case of H2O, the total number of electron pairs in their valence shells is four.
3. Choosing the central atom.
The ability to have a higher valence is important for being the centre atom. Therefore, Oxygen will be the central atom.
4. Mark atom with lone pairs.
- There are four electron pairs in total, with two H-O bonds already present in the sketch structure.
- There are only two electron pairs left to mark on atoms which cannot be done on the outside atoms – hydrogen as it cannot hold more than two electrons in its last shell.
- As a result, the two electron pairs are marked on the central atom – oxygen.
5. If there are charges on atoms, mark them.
The oxygen and hydrogen atoms have no charges.
6. To obtain the best Lewis structure minimise charges on atoms by converting lone pairs to bonds.
Since there are no charges on atoms, there is no need to reduce charges as part of the process of drawing the best Lewis structure. We already have the best Lewis structure for H2O.
7. Check the stability of each atom
It can be checked by using the formula-
Formal charge = Valence Electrons – Unbonded Electrons – ½ Bonded Electrons
| Elements | Oxygen | Hydrogen |
|---|---|---|
| Formula Applied | Valence electrons = 6
Lone pair electrons = 4 Shared pair electrons (2 single bond) = 4 |
Valence electrons = 1
Lone pair electrons = 0 Shared pair electrons (1 single bond) = 2 |
| Formal Charge | (6 – 4 – 4/2) = 0 | (1 – 0 – 2/2) = 0 |
Since the overall formal charge is zero, the above Lewis structure of H2O is most appropriate, reliable, and stable in nature.
Molecular Geometry of H2O
The oxygen atom forms two single sigma bonds with the hydrogen atoms in the H2O molecule. Although these two Hydrogen atoms are symmetrically arranged in the plane, the two lone pairs of electrons on the Oxygen atom push these atoms.
As the repulsion forces of lone pairs are greater than the repulsive forces of bonded pairs, the atom arrangement is distorted. As a result, the water molecule’s molecular geometry is angular or v-shaped.
The bond angle in a water molecule (104.5°)
Hybridization of H2O
The Lewis structure shows two single sigma bonds between the oxygen and hydrogen atoms. Besides that, these bonds leave the oxygen atom with two lone pairs of electrons.
The H2O molecule’s hybridization is sp3 because it has one s orbital and three p orbitals that combine to form four hybrid orbitals.
Polarity of H2O
Water H2O is a polar substance. This is due to the bent shape of the water molecule, which causes an unequal charge distribution over the hydrogen and oxygen atoms in the water molecule. As a result, the water molecule has a net dipole moment.
Frequently Asked Questions on Lewis Structure of H2O
What is the shape of the water molecule?
The shape of the water molecule is bent. This is due to the repulsion forces of lone pairs.
In the Lewis structure H2O, how many lone pairs are there on the oxygen atom?
There are only two lone pairs on the oxygen atom. Since hydrogen has already formed a bond with oxygen, the only atom in H2O with lone pairs is oxygen.
What are some examples of similar Lewis structures to water that can be drawn?
The Lewis structures of hydrogen sulphide (H2S) and oxygen difluoride (F2O) are similar to those of water.
What is the total number of valence electrons available for drawing the Lewis structure of water?
The total number of valence electrons available for drawing the Lewis structure of water is 8.
What is the reason for the polarity of a water molecule?
The water molecule is bent in shape, which causes an unequal charge distribution over the hydrogen and oxygen atoms. As a result, the water molecule has a net dipole moment.
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