Question

At room temperature, water is a liquid, but carbon dioxide is a gas. Both compounds are molecules made of three atoms. What must be occurring at the atomic level for water to be a liquid and carbon dioxide a gas at the same temperature?

Answer 1

Water remains liquid at room temperature due to strong hydrogen bonds that give it a high boiling point, whereas carbon dioxide is a gas at room temperature because it has weaker London dispersion forces and sublimates at standard atmospheric pressure.

Step-by-step explanation:

To understand why water is a liquid and carbon dioxide is a gas at room temperature, we need to look at the physical properties and intermolecular forces present in each. Water molecules have strong hydrogen bonds due to the polarity of the water molecule (H2O), which means each hydrogen is covalently bonded to a highly electronegative oxygen atom. These hydrogen bonds are responsible for water's relatively high boiling point of 100°C, allowing it to exist as a liquid at room temperature, which is typically around 20°C.

In contrast, carbon dioxide (CO2) molecules are linear and nonpolar, lacking hydrogen bonding. The primary intermolecular force holding CO2 molecules together is the weaker London dispersion forces, which are not sufficient to keep it as a liquid at room temperature, resulting in a gas state. Additionally, CO2 sublimates at standard atmospheric pressure, transitioning directly from a solid to a gas at temperatures below its sublimation point.

Therefore, for a compound to be a liquid at room temperature, its boiling point must be above room temperature. The stronger the intermolecular forces, specifically hydrogen bonding in the case of water, the higher the boiling point and the more likely the substance is to be a liquid at room temperature.