Question

Oxygen atoms are used to make water molecules. Does this mean that oxygen, \(\mathrm{O}_{2}\), and water, \(\mathrm{H}_{2} \mathrm{O}\), have similar properties? Why do we drown when we breathe in water despite all the oxygen atoms present in this material?

Short answer

Oxygen in water is not in a gaseous form, so it doesn't supply oxygen for respiration like \(\mathrm{O}_{2}\) .

Step-by-step solution

Understanding Molecular Composition

Water (\(\mathrm{H}_{2}\mathrm{O}\)) is composed of two hydrogen atoms and one oxygen atom, whereas oxygen gas (\(\mathrm{O}_{2}\)) consists of two oxygen atoms bonded together. This means the composition of water and oxygen gas is different.

Analyzing Molecular Properties

The properties of a substance depend on its molecular composition and structure. In \(\mathrm{O}_{2}\), the oxygen molecules are in a gaseous state, while in \(\mathrm{H}_{2}\mathrm{O}\), the hydrogen and oxygen are bonded to form liquid water, leading to different physical and chemical properties.

Function of Elemental Oxygen vs. Water

Elemental oxygen (\(\mathrm{O}_{2}\)) is a gas required for respiration in most organisms, while water (\(\mathrm{H}_{2}\mathrm{O}\)) is a liquid that does not support aerobic respiration. Therefore, breathing in water leads to drowning because the lungs cannot extract \(\mathrm{O}_{2}\) needed for breathing from \(\mathrm{H}_{2}\mathrm{O}\) molecules.

Key concepts

Molecular Composition

Understanding molecular composition is crucial to differentiate between substances even if they share some common elements. In the case of water and oxygen gas, both contain oxygen atoms, yet they are vastly different due to their molecular arrangements. Water, \(\mathrm{H}_{2}\mathrm{O}\), is composed of two hydrogen atoms bound to a single oxygen atom. This results in a stable, polar molecule that forms liquid under normal conditions. In contrast, oxygen gas, \(\mathrm{O}_{2}\), consists solely of diatomic oxygen molecules, meaning two oxygen atoms are bonded together. This simple bond creates a gaseous state that's essential for breathing.
The distinct molecular composition directly influences the behavior and properties of the substances. Even a small change, like adding or removing specific atoms, can hugely impact how a molecule functions and interacts with its environment.

Oxygen Gas

Oxygen gas, represented chemically as \(\mathrm{O}_{2}\), is a diatomic molecule essential for life. This simple yet vital molecule plays a critical role in various biological and chemical processes.

• Most importantly, it supports aerobic respiration, which is the process of producing cellular energy using oxygen.
• Oxygen gas is colorless, odorless, and classically associated with life-support systems due to its vital role in breathing.
• In nature, oxygen constitutes approximately 21% of the Earth's atmosphere, providing the environment necessary for organisms that rely on it for survival.

Oxygen's unique properties result from its diatomic form, which enables it to easily dissolve in water, participate in combustion, and act as an oxidizing agent.

Water Molecule

The water molecule, \(\mathrm{H}_{2} \mathrm{O}\), is a chemical compound composed of two hydrogen atoms and one oxygen atom. This configuration results in a bent molecular shape which causes the molecule to be polar, meaning it has opposite electrical charges on each end.

• This polarity allows water molecules to form hydrogen bonds with each other, accounting for its high boiling and melting points compared to other molecules of similar size.
• Water is a universal solvent, making it essential in biological systems for transporting nutrients and waste within organisms.
• The liquid state of water at room temperature makes it a habitat for countless aquatic life forms and an integral part of Earth's ecosystems.

Despite containing oxygen, the essential component for life, water in its bonded form cannot be used by our bodies in the same way as oxygen gas.

Respiration

Respiration is the biological process that allows organisms to obtain energy from nutrients, and it typically involves oxygen. In humans and many other species, aerobic respiration is the process that uses oxygen gas, \(\mathrm{O}_{2}\), from the environment to convert glucose into energy, carbon dioxide, and water.

• Oxygen is transported to cells, where it acts as the final electron acceptor in the mitochondrial electron transport chain, a critical step of cellular respiration.
• This process releases energy stored in glucose molecules into a form that cells can readily use, known as ATP (adenosine triphosphate).
• While water is a byproduct of respiration, it cannot be used in place of molecular oxygen to fuel this process.

This limitation explains why inhaling water instead of air leads to drowning. No matter how oxygen-rich water molecules are, they fail to provide the gaseous oxygen our bodies require to thrive.