Why is water \(\mathrm{H}_{2} \mathrm{O}\) and not \(\mathrm{H}_{3} \mathrm{O}\) or something else? Justify your answer with dot diagrams.

To justify the chemical formula of water, we will use Lewis structures, which help us visually understand the bonding between atoms in a molecule. In these diagrams, the valence electrons (outer shell electrons) are represented by dots around the element symbol.

In order to draw the Lewis structure for water, we must first identify the number of valence electrons for each atom. Each hydrogen atom has 1 valence electron, while each oxygen atom has 6 valence electrons. This will help us determine how the atoms bond together.

When creating a Lewis structure, we want to ensure that each atom achieves the desired number of valence electrons. Hydrogen requires 2 electrons to achieve a full outer shell, while oxygen requires 8 electrons. In the H2O molecule, the oxygen atom is in the center, with one hydrogen atom on each side. The oxygen atom forms 2 single covalent bonds, one with each hydrogen atom. These single bonds consist of 2 electrons each, one from the hydrogen atom and one from the oxygen atom. So, the final Lewis structure for H2O is: O / \ H H Here, the oxygen atom has 8 valence electrons (2 in each bond and 4 nonbonding electrons), satisfying the octet rule, and each hydrogen atom has 2 valence electrons, satisfying the duet rule.

If we were to consider an H3O molecule, an oxygen atom would need to form covalent bonds with 3 hydrogen atoms. However, oxygen only has 2 available bonding sites (it has 2 unpaired electrons from its 6 valence electrons). Forming another bond with a hydrogen atom would mean that oxygen would not follow the octet rule, as it would have 10 valence electrons. Therefore, a stable H3O molecule cannot exist. In conclusion, the Lewis structure for water, H2O, demonstrates the stable bonding of two hydrogen atoms and one oxygen atom. This stability is achieved by satisfying the octet rule for oxygen and the duet rule for hydrogen. As the bonding in H3O or any other chemical formula would not follow these rules, water is H2O and not H3O or something else.