Water and Its Polarity

By the end of this lesson and the next few, you should be able to 

  • Describe the properties of water that are critical to maintaining life
  • Explain why water is an excellent solvent
  • Provide examples of water’s cohesive and adhesive properties
  • Discuss the role of acids, bases, and buffers in homeostasis

Water

Why do scientists spend time looking for water on other planets? Why is water so important? It is because water is essential to life as we know it. Water is one of the more abundant molecules and the one most critical to life on Earth. In fact, water makes up approximately 60–70 percent of the human body. Without it, life as we know it simply would not exist.

water

Image Attribution: Sven Hoppe/Wikimedia Commons (CC BY-SA 3.0)

The polarity of the water molecule and its resulting hydrogen bonding make water a unique substance with special properties that are intimately tied to the processes of life. Life originally evolved in a watery environment. In fact, most of an organism’s cellular chemistry and metabolism occur inside the watery contents of the cell’s cytoplasm.

Special properties of water are its high heat capacity and heat of vaporization, its ability to dissolve polar molecules, its cohesive and adhesive properties, and its dissociation into ions that leads to the generation of pH. Understanding these characteristics of water helps to elucidate its importance in maintaining life.

Water’s Polarity

One of water’s important properties is that it consists of polar molecules: the hydrogen and oxygen within water molecules (H2O) form polar covalent bonds. While there is no net charge to a water molecule, the polarity of water creates a slightly positive charge on hydrogen and a slightly negative charge on oxygen, contributing to water’s properties of attraction.

Water’s charges are generated because oxygen is more electronegative than hydrogen, making it more likely that a shared electron would be found near the oxygen nucleus than the hydrogen nucleus, thus generating the partial negative charge near the oxygen.

As a result of water’s polarity, each water molecule attracts other water molecules because of the opposite charges between water molecules, forming hydrogen bonds. Water also attracts or is attracted to other polar molecules and ions.

nonpolar-molecules

Oil and water do not mix. As this macro image of oil and water shows, oil does not dissolve in water but forms droplets instead. This is due to it being a nonpolar compound. Image Attribution: Gautam Dogra, OpenStax Biology.

A polar substance that interacts readily with or dissolves in water is referred to as hydrophilic (hydro- for “water” and -philic for “loving”). In contrast, non-polar molecules such as oils and fats do not interact well with water (see image above). They separate from water rather than dissolve in it, as we see in salad dressings containing oil and vinegar (an acidic water solution). We call these nonpolar compounds, hydrophobic (hydro- for “water”and -phobic for “fearing”).

How polarity makes water behave strangely

Water is both essential and unique. It consists of two hydrogen atoms and one oxygen, therefore creating an unequal sharing of electrons. Many of its particular qualities stem from this fact. From fish in frozen lakes to ice floating on water, Christina Kleinberg describes the effects of polarity in the TED-Ed video below.

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This is a lesson from the tutorial, Chemical Foundation of Life and you are encouraged to log in or register, so that you can track your progress.

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