Slide 1
Water is essential to life as we know it. It is a strange
substance with special properties that allow it to be found normally on
earth in all three states of matter: solid, liquid, and gas.
Water is so integral to our understanding of life that when we look for life on other planets - we look for signs of water. Launched in August 2007, the Phoenix Mars Mission was designed to study the history of water and habitability potential in the Martian arctic's ice-rich soil. In May of 2010 the Phoenix Mars Lander ended operations due to excessive ice damage to the lander.
Slide 2
The molecular formula of water is H20 - two hydrogen atoms
covalently bonded to an oxygen atom. Oxygen is highly electronegative - this
means that it tends to attract electrons and thus the oxygen end of the
water molecule has a slight negative charge. The hydrogen end of the
molecule has a slight positive charge. This distribution of charge
across the molecule makes water a polar molecule.
This distribution of charge also results in the formation of hydrogen bonds between the positively charged hydrogen end of a water molecule and the negatively charged oxygen end of neighboring water molecules.
Slide 3
The hydrogen bonds that form between water molecules make the
water molecules stick together. This contributes to some of the unique
properties of water that make life possible.
For example, water has cohesion - which means that the water molecules stick together. The result is that there is surface tension at the surface of water (whether a pond, a glass of water, or a drop of water). This surface tension can be used by some organisms as a walking surface - such as water striders that can walk on water.
Water also has adhesion - which means that the water molecules will stick to another surface - such as the surface of a leaf or inside the vascular tissue of a plant. This adhesion allows plants to transport water (using capillary action) from the soil all the way to the leaves so photosynthesis can take place.
Slide 4
Water also has high specific heat and a high heat of
vaporization. The specific heat is the amount of heat per unit mass
required to raise the temperature by one degree Celsius. The specific
heat of water is 1 calorie/gram which is higher than any other common
substance. As a result, water plays a very important role in temperature
regulation. This is particularly important near large bodies of water
like the oceans - the oceans play an important role and regulating the
global temperature.
The heat of vaporization is the amount of heat required to convert unit mass of a liquid into the vapor without a change in temperature. The heat of vaporization of water is higher than other common substances - this helps us to cool ourselves during hot weather. When we sweat, our skin becomes covered with water. If humidity is low, this water evaporates easily. The heat energy needed for this evaporation comes from our bodies - so sweating and evaporative cooling cools our bodies. The higher the humidity - the more water there is in the air - and the less evaporation takes place. This is why it is hard to cool down on hot, humid days.
Solid water is less dense than liquid water - this is also an usual property for matter to have. The result is that ice floats and organisms can live under the ice. If ice sank - bodies of water would tend to freeze solid in the winter and organisms could not survive.
Slide 5
Water is also an excellent solvent - which means that many things
dissolve in water. For example, when you put crystalized salt and
sugar in water - it dissolves.
However, water is not a perfect solvent - which is basically a good thing but can sometimes have negative consequences. It is a good thing because we would not want our skin and bones to dissolve in water - life would not be possible.
But it is a bad thing when nonsoluble hydrocarbons (these are nonpolar chains of carbon and hydrogen) get released into the water. This is what happens in an oil spill - oils are hydrocarbons and all hydrocarbons behave hydrophobically - they do not interact with water. When organisms become coated in oil - that oil cannot wash off because it does not interact with the water. The result is that the animal can become weighted down by the oil and drown, or the oil can disrupt the natural coating on an animal such as a bird and leave the bird suseptible to becoming too cold or too hot. Some animals will ingest the oil in an effort to clean themselves - the oil is toxic and can cause death.