Understanding Chemical Attractions Between Polar Molecules: Hydrogen Bonding in Water

Understanding the chemical attractions between polar molecules is crucial in chemistry and biochemistry. A prime example of this phenomenon is the hydrogen bonding that occurs between water molecules, which is a manifestation of the weak chemical attraction between polar molecules. In this article, we will delve deeper into the nature of hydrogen bonds, explore their role in water's properties, and discuss their significance in biological and chemical systems.

Understanding Polar Molecules

Polar molecules are substances in which the electrons are not evenly distributed between the atoms within the molecule (Figure 1). This uneven distribution results in an overall separation of electrical charges, with one end of the molecule being slightly positive and the other end being slightly negative. Water (H2O) exemplifies a polar molecule, where the oxygen atom is more electronegative than the hydrogen atoms and thus holds the electrons closer to itself, creating a partial negative charge on the oxygen side and partial positive charges on the hydrogen sides.

What is a Hydrogen Bond?

A hydrogen bond is a special type of intermolecular attraction between a hydrogen atom bonded to a highly electronegative atom and an electronegative atom in another molecule (Figure 2). In a water molecule, the positively charged hydrogen atoms can attract the negatively charged oxygen atoms of other water molecules, creating hydrogen bonds (Nahm et al., 2018). These bonds are weaker than covalent or ionic bonds but are still significant in influencing the physical and chemical properties of water and other polar substances.

The Role of Hydrogen Bonds in Water

Water is a very distinctive substance due to its hydrogen bonding capabilities. This weak chemical attraction is pivotal in determining many of its unique properties. Here are some key points:

Boiling Point: Water has a high boiling point compared to similar molecules such as methane (CH4) or ammonia (NH3) (Lide, 1998).

Density: Unlike most substances, water is at its maximum density at 4 °C (Lide, 1998).

Melting Point: The melting point of water is positive (0 °C), unlike many substances (Lide, 1998).

Tension: Water has a high surface tension due to hydrogen bonding, which allows insects to walk on water (O'Leary, 2000).

Significance of Hydrogen Bonding in Biological and Chemical Systems

The hydrogen bonding between polar molecules like water molecules plays a crucial role in biological systems and in various chemical processes. Here are some of the applications and significance:

Protein Stability: In proteins, hydrogen bonding helps to maintain the secondary and tertiary structures, contributing to the overall stability of the protein (Lide, 2000).

DNA Structure: Hydrogen bonding is one of the major forces maintaining the double helix structure of DNA, essential for genetic information storage and replication (Alberts et al., 2013).

Hydrophobic Interactions: Nonpolar substances often interact with each other through dispersion (London) forces, while the polar regions of water molecules try to avoid these interactions, a phenomenon fundamental to many biomolecular processes (Alberts et al., 2013).

Conclusion

Understanding the chemical attraction between polar molecules, particularly through hydrogen bonding, is vital for comprehending water's unique properties and its role in biological and chemical systems. Hydrogen bonding in water exemplifies the weak yet important chemical attraction that significantly influences the physical world around us. Further research into these phenomena could provide insights into new technologies and applications in science, medicine, and engineering.

References

Alberts, B., Johnson, A., Lewis, J., Raff, M., Roberts, K., Walter, P. (2013). Molecular Biology of the Cell. Garland Science.

Lide, D. R. (Ed.). (1998). CRC Handbook of Chemistry and Physics.

Lide, D. R. (2000). CRC Handbook of Chemistry and Physics.

Nahm, M. M., Byeon, Y. S., Ho, T. (2018). Chemistry Today: With Access. Oxford University Press.

O'Leary, B. (2000). Surface Tension. Science World.