Comparison of Molecule Sizes: Air vs Water

When comparing the sizes of molecules that make up air (nitrogen, oxygen, carbon dioxide) with water molecules, several factors come into play, including molecular weight and structure. Understanding these differences can provide insights into the behavior and properties of these molecules in various environments.

Molecular Weights and Structures

To compare the sizes of air molecules like nitrogen (N2), oxygen (O2), and carbon dioxide (CO2) with water molecules (H2O), we can examine their molecular weights and structures:

Nitrogen (N2)

Molecular weight: ~28 g/mol Composition: 14 g/mol per nitrogen atom Structure: Diatomic molecule, relatively simple

Oxygen (O2)

Molecular weight: ~32 g/mol Composition: 16 g/mol per oxygen atom Structure: Diatomic molecule

Carbon Dioxide (CO2)

Molecular weight: ~44 g/mol Composition: 12 g/mol for carbon, 16 g/mol for each oxygen Structure: Linear molecule

Water (H2O)

Molecular weight: ~18 g/mol Composition: 1 g/mol per hydrogen atom, 16 g/mol for oxygen Structure: Bent molecule

Size Comparison

The size of a molecule is generally related to its molecular weight and structure, but it isn't entirely determined by these factors. In terms of molecular geometry, water (H2O) has a bent shape, while nitrogen (N2) and oxygen (O2) are diatomic and linear, and carbon dioxide (CO2) is also linear.

While individual air molecules may have higher molecular weights than water, the actual size can vary. In terms of molecular size, water molecules are compact but not necessarily smaller than nitrogen or oxygen molecules. The differences in size are not very significant when comparing these common molecules.

Estimating Molecular Dimensions

While specific molecular dimensions can vary, estimated values provide a general sense of size:

N2: Approximately 28 ? O2: Approximately 32 ? CO2: Approximately 44 ? H2O: Approximately 18 ?

For the construction engineer's question on why breathable vapor barrier membranes allow air to penetrate but not water/vapor molecules, the reason lies in the size difference. Air molecules, being significantly smaller, can more easily pass through the membrane, while water vapor molecules are larger and thus are blocked.

It is generally accepted that out of the molecules we've discussed, water (H2O) is indeed small, with the hydrogen atom being the second smallest, only helium being smaller. In the context of these molecules, the two hydrogen atoms in water are tightly bound to the oxygen atom, making water molecules compact compared to others.

Carbon dioxide (CO2) is definitely the largest among the molecules mentioned here, with a linear structure and higher molecular weight contributing to its larger size.