What is the importance of an H-bond in water?
It raises the boiling point of water; otherwise, following the sequence of H2Te, H2Se, H2S and H2O, the H2O would be a gas.
The importance of hydrogen bonds in water is closely tied to the unique properties of water as a liquid. Hydrogen bonding refers to the attractive force between a hydrogen atom (covalently bonded to an electronegative atom) and an electronegative atom of a different molecule.
In water, each molecule consists of two hydrogen atoms bonded to an oxygen atom in a bent shape. Due to the unequal sharing of electrons, oxygen becomes slightly more electronegative than hydrogen, creating a partial positive charge (δ+) on the hydrogen atoms and a partial negative charge (δ-) on the oxygen atom.
Hydrogen bonds form between the positive end of one water molecule (hydrogen atom) and the negative end of another water molecule (oxygen atom). These hydrogen bonds are responsible for many important properties of water:
1. Cohesion: Hydrogen bonds give water high cohesion, meaning water molecules are strongly attracted to each other. This allows water to form droplets, flow in a continuous manner, and pull itself up through small tubes (capillary action).
2. High boiling point and specific heat: Hydrogen bonds contribute to the high boiling point and specific heat capacity of water. It takes a significant amount of energy to break the hydrogen bonds between water molecules, which is why water has a relatively high boiling point compared to similar compounds. Additionally, the ability of water to absorb and store large amounts of heat without a significant increase in temperature is crucial for maintaining stable temperatures in living organisms and regulating Earth's climate.
3. Surface tension: Hydrogen bonding also gives water a high surface tension, allowing insects, for example, to walk on the surface of water without sinking. This is due to the cohesive forces that hold water molecules together at the surface.
4. Solvent properties: Water is an excellent solvent due to its ability to form hydrogen bonds with other polar and ionic substances. This solvent property is fundamental to many biological and chemical processes occurring in living organisms.
Therefore, the presence of hydrogen bonds in water is crucial in explaining its unique properties and its role as a vital substance for life.