Lesson 7 Properties of Ionic and Molecular Compounds
Special Properties of Water
Did you know that water is called the universal solvent?
B7.12 Various solutions
Water is a very special compound with a unique set of properties. The properties result from the bonding and structure of the water molecule. The term “universal solvent” means that water has the ability to dissolve many different types of substances.
Did You Know?
B7.17 Spring turnover in a lake
Did you know that water is its most dense at 4 °C. This important property accounts for the fall and spring turnover in lakes that keeps lakes from becoming stagnant or freezing solid. As surface water reaches 4 °C, it becomes denser and sinks.
Water is a molecular compound and has covalent bonds in which electrons are shared between the oxygen atom and the hydrogen atoms. These electrons are not shared equally; the oxygen has a stronger pull on the electrons and holds them closer
to its nucleus.
Since the electrons are closer to the oxygen, the oxygen will be slightly negative (because electrons are negative) and the hydrogen atoms will be slightly positive.
This uneven sharing results in water being a polar molecule. These charges result in attraction between water molecules. Forces of attraction between molecules are called intermolecular forces. Specifically, for water, these are called hydrogen bonds. The polar ends of water will also cause attraction to other charged particles.
Since the electrons are closer to the oxygen, the oxygen will be slightly negative (because electrons are negative) and the hydrogen atoms will be slightly positive.
This uneven sharing results in water being a polar molecule. These charges result in attraction between water molecules. Forces of attraction between molecules are called intermolecular forces. Specifically, for water, these are called hydrogen bonds. The polar ends of water will also cause attraction to other charged particles.
In addition to water’s ability to dissolve both ionic and other polar molecules, there are several other properties that are a result of water’s polar structure.
The electrostatic attraction (attraction between positive and negative charges) between water molecules is strong, so it takes a lot of energy to move the water molecules apart (which is what melting and boiling essentially is).
When water molecules bond together to form ice, they form in a hexagonal pattern (so that there is a maximum number of positive and negative interactions between water molecules). This creates a six-sided solid structure in which water
molecules are farther apart than in the liquid form, causing water to be less dense as a solid.
Increasing temperature means that particles move more. It takes a lot of energy to raise the temperature of water because of the strong attraction between molecules holding them in place.
Water molecules are strongly attracted to each other (aides in the transport of water in plants).
Water molecules are strongly attracted to other particles (aides in the transport of minerals in plants).
The attraction between water molecules at the surface of a liquid causes them to stick together and create a “film” on the surface that allows insects to walk on water.
Watch This
Why Does Ice Float in Water @ YouTube TED-Ed
Watch this video that will go over some unique properties of water.
Read This
Please read pages 60 and 61 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on the structure and properties of
water. Remember, if you have any questions or you do not understand something, ask your teacher! Practice Questions
Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice
questions in your notes. After you have checked your answers, make corrections to your responses (where necessary) to study from.-
What is a polar molecule? Provide an example.
A polar molecule is a neutral molecule that has partial charges on atoms due to uneven electron sharing. Water is a polar molecule.
B7. 18 Polar water molecule - Using your own words, explain why water has high melting and boiling points.
Because water molecules are polar, they form strong attractions between neighbouring molecules. It takes a lot of energy to break these forces of attraction and move the molecules farther apart.
B7.19 Attraction between two water molecules