The liquid state of water at room temperature is as a result of

Analysis

The question asks why water exists as a liquid at room temperature, despite having a relatively low molecular mass compared to other substances that are gases at the same temperature.

Concept Explanation

To understand this, we must look at Intermolecular Forces. These are the forces of attraction that exist between molecules.

• Covalent bonds (Option B) exist within the water molecule (between the Oxygen and Hydrogen atoms). These are very strong, but they do not determine the physical state (solid, liquid, or gas) of the substance.
• Hydrogen bonding is a special, strong type of dipole-dipole attraction that occurs when a hydrogen atom is covalently bonded to a highly electronegative atom (like Oxygen, Nitrogen, or Fluorine).
• In water ($H_2O$), the oxygen atom is highly electronegative and pulls the shared electrons towards itself, creating a partial negative charge ($\delta-$) on the oxygen and a partial positive charge ($\delta+$) on the hydrogen atoms. This causes the hydrogen of one water molecule to be strongly attracted to the oxygen of a neighboring water molecule.

Step-by-Step Solution

1. Identify the forces: Water molecules are held together by hydrogen bonds.
2. Evaluate the effect: Because hydrogen bonds are significantly stronger than standard dipole-dipole interactions or Van der Waals forces, they require more energy (heat) to break.
3. Relate to state: At room temperature, the kinetic energy of water molecules is not high enough to overcome these strong hydrogen bonds. Consequently, the molecules remain "tethered" together in a liquid state rather than escaping into the atmosphere as a gas.
4. Conclusion: If water did not have hydrogen bonding, it would be a gas at room temperature (similar to $H_2S$, which is a gas because it lacks significant hydrogen bonding).

Identifying the Answer

• A. Electrovalent bond: Incorrect; this involves the transfer of electrons between ions (e.g., in NaCl).
• B. Covalent bond: Incorrect; this holds the atoms inside the molecule together, not the molecules to each other.
• C. Van der Waals forces: Incorrect; these are weak forces present in all molecules, but they are not the primary reason for water's liquid state.
• D. Hydrogen bond: Correct. This is the specific intermolecular force responsible for the high boiling point and liquid state of water at room temperature.

Exam Tip

Whenever you see a question about the physical properties of water (like its high boiling point, surface tension, or liquid state), always look for "Hydrogen bonding" as the keyword. It is a favorite topic for JAMB examiners!