Question

The boiling point of water is exceptionally high because (a) there is covalent bond between \(\mathrm{H}\) and \(\mathrm{O}\) (b) water molecule is not linear (c) water molecule is linear (d) water molecules associate due to hydrogen bonding

Short answer

Option (d): Water's high boiling point is due to hydrogen bonding.

Step-by-step solution

Understanding the Question

The question asks us to determine why water has a high boiling point compared to other similar molecules. It offers four options, and we need to choose the correct explanation based on our understanding of molecular interactions.

Examining Option (a)

Option (a) suggests that the high boiling point is due to the covalent bond between  ext{H} and  ext{O}. While water does have covalent bonds, these bonds are not directly responsible for its high boiling point, as many molecules with covalent bonds do not have significantly high boiling points.

Examining Option (b)

Option (b) suggests that the shape of the water molecule, which is not linear, is the reason for the high boiling point. While the bent shape contributes to polarity, it is not the direct reason for the high boiling point.

Examining Option (c)

Option (c) suggests water is linear, which is incorrect. The water molecule is bent, not linear, so this cannot be the reason for the high boiling point.

Examining Option (d)

Option (d) states that water molecules associate due to hydrogen bonding. This is correct, as the strong hydrogen bonds between water molecules result in a higher boiling point since more energy is required to break these bonds.

Selecting the Correct Answer

After reviewing all options, (d) is the correct choice because hydrogen bonding is the main reason for water's high boiling point compared to other similar molecules without such strong intermolecular forces.

Key concepts

Boiling Point

The boiling point of a substance is the temperature at which its liquid state transforms into a gas. At this point, the vapor pressure of the liquid equals the surrounding atmospheric pressure. For water, the boiling point is notably higher than many similar-sized molecules. This property is essential for various biological and environmental processes, ensuring the regulation of temperatures in living organisms and the environment.

At its core, boiling point is influenced by the strength of molecular interactions. In essence, if molecules are bound strongly together, it will require more energy or heat to separate them, resulting in a higher boiling point. In the case of water, these strong interactions are predominantly due to hydrogen bonding.

Molecular Interactions

Molecular interactions account for how molecules attract or repel each other and are vital in determining a substance's physical properties, like boiling and melting points. The key interactions include hydrogen bonds, ionic interactions, van der Waals forces, and covalent bonds.

When we talk about water, hydrogen bonds dominate its molecular interactions. These interactions arise because of the strong attraction between the slightly positive hydrogen atom of one water molecule and the slightly negative oxygen atom of another. This unique type of bond is primarily responsible for the high boiling point of water compared to other molecules of similar size.

• Hydrogen bonding significantly increases the cohesiveness of water molecules.
• More energy is required to break these bonds, hence higher boiling point.

The stronger the intermolecular forces, the higher the boiling point. Water, with its extensive hydrogen bonding, serves as a classic example.

Covalent Bonds

Covalent bonds refer to the chemical bond formed when two atoms share one or more pairs of electrons. This type of bond is prevalent in organic compounds and many molecular substances, including water.

The covalent bond between hydrogen and oxygen in a water molecule is a single covalent bond. Each hydrogen atom shares an electron with the oxygen atom, resulting in a stable molecular structure.
However, it's important to note that, although these bonds form the basis of water's structure, they are not directly responsible for its high boiling point. The high boiling point is primarily a result of strong hydrogen bonds between water molecules, rather than the covalent bonds within the molecule itself.

Molecular Shape

The shape of a molecule greatly impacts its chemical and physical properties, such as polarity and intermolecular forces. Water, for instance, has a bent shape, with an angle of approximately 104.5 degrees between its hydrogen atoms.

• The bent shape contributes to its polar nature, as there is an uneven distribution of charges within the molecule.
• This polarity allows water molecules to form hydrogen bonds effectively, enhancing the intermolecular attraction between them.

Though the molecular shape contributes to creating polarity that facilitates hydrogen bonding, it's not the sole reason for water's high boiling point. The bent shape merely supports the hydrogen bonding, while the hydrogen bonds themselves are the direct cause of water's high boiling point. Understanding the shape and arrangement of atoms in molecules helps explain many of their behaviors, especially in interactions with other molecules.