Properties of Water
Topics Covered: Water, polarity, hydrogen bonding, cohesion, adhesion, specific heat capacity, density
We all know that water is essential for our lives (if you didn’t know that, maybe try living without water for a day?) But what makes water unique? In this post, we will cover the structure of water molecules and different properties of water that make water special.
A water molecule, commonly known as H2O, consists of two hydrogen atoms and one oxygen atom. Oxygen is more electronegative than hydrogen (electronegativity is an atom's tendency to attract shared electrons), so oxygen strongly pulls electrons from hydrogen to the oxygen side. This unequal distribution of electrons makes the oxygen side partially negative and the hydrogen side partially positive, making water a polar molecule.
The polarity of water contributes to water’s hydrogen bonding. As we discussed in our previous post about intermolecular forces, the partial positive hydrogen end of a water molecule attracts the partial negative oxygen end of the other water molecule, forming a hydrogen bond between adjacent water molecules.
This attraction between the water molecule and another water molecule is also known as cohesion. On the other hand, the attraction between the water molecule to other molecules (like polar, charged and ionic molecules) is called adhesion!
Besides cohesion and adhesion, water also has a high specific heat capacity. Specific heat capacity is the amount of heat required to raise 1g of substance by 1℃. Because it requires a huge amount of heat to increase the temperature of water, water changes temperature very slowly. And this helps life on earth because unlike the land, the sea doesn’t change the temperature very quickly, allowing marine organisms to live in the ocean!
Lastly, another unique property of water is that water is less dense as a solid than a liquid. Unlike most other substances, water molecules are farther apart when they are in a solid state, so ice floats on liquid water! Why is this important? Well, because of this property, only the top of the lake or pond freezes in winter, acting as an insulative layer and thus protecting the organisms beneath the surface from freezing!
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