Cascades to Coast

Why can't we see some gases?

We cannot see some gases because of two reasons, absorption of visible light and phase properties.
1) We do "see" some gases because they absorb visible light, i.e. some gases appear colored.
2) The molecules in gases are far apart and spread out when in the gas phase. Molecules and the atoms that make up molecules are very small. However, when those molecules change to a different state such as a liquid or solid, the molecules come near each other and take a different form and we are able to see them. For example, carbon dioxide is a gas we cannot see. However, as you decrease temperature, the carbon dioxide molecules condense and move closer together and become a solid that is dry ice. Dry ice is something we can see because the molecules are in a solid state now.