BELLRINGER  Answer the following questions  “How do you think the words molecules, elements, and atoms are related?”  “What does water look like?”

PROPERTIES OF WATER Chapter 2.2

WE NEED WATER!  Everything that makes you up depends on water.  All life processes take place in a watery environment  How water is shaped plays a role in why it is used in your body.

ATOMIC STRUCTURE

POLARITY  Water is a polar molecule  This means one end of the molecule is negative and one end is positive  Oxygen is negative  Hydrogen is positive  This means water is attracted to similar polar molecules  So, water likes other water molecules

NON-POLAR  There are also non-polar molecules.  This means they do not have differently charged regions on them.  Fats are common non-polar molecules  What happens when you try to mix water and fat?

WATER AND OIL Notice the separation between the two fluids. The oil is hydrophobic, so it is repulsed by the water. This causes the oil to stick together and separate itself from the water in a dramatic fashion. This can also be noticed if you’ve ever had oil and vinegar. If you wanted to use that on a salad, you would have to shake it up first so the oil and vinegar infuses together more easily.

HYDROGEN BONDS  Hydrogen bonds are attractions between slightly positive hydrogen atoms and slightly negative oxygen atoms (sometimes nitrogen)  These are so important that they are even used to support your DNA as well as protein folding.

Fig. 3-2 Hydrogen bond  – – H  + + H O — —  + +  + +  + +  – –  – –  – –

HYDROGEN BONDS  An individual hydrogen bond is much weaker than a covalent bond.  These bonds are the reason why water is liquid much of the time.  There are 4 very important properties of hydrogen bonds (which you need to remember)

5 PROPERTIES OF H 2 0  High Specific Heat  Water resists change in temperature.  This means water has to absorb heat to rise in temperature  Think about cells – why would this be really important?

5 PROPERTIES OF H 2 0  Cohesion  Attraction among molecules of the same substance.  Water likes other water molecules, so they stick to each other easily  This is why water beads on windows, forms droplets.  Gives surface of water (called surface tension)

Fig. 3-4

5 PROPERTIES OF H 2 0  Adhesion  Attraction of water molecules to different substances.  This is why water “climbs” up the edge of a test tube.  What about plants?  You will need to be able to distinguish the differences between all 3 of these properties. Make sure you never forget them!

Fig. 3-3 Water-conducting cells Adhesion Cohesion 150 µm Direction of water movement

5 PROPERTIES OF H 2 0  Water is considered the most common solvent in biology  Molecules and ions can’t form in a non-water environment.  Big molecules have to be dissolved before they can move.  This is why water is called the “universal solvent”.

5 PROPERTIES OF H 2 0  When water freezes, it expands.  This is because the energy within the molecules has slowed down, allowing for longer lasting hydrogen bonds.  Helps protect and insulate organisms in water systems (e.g. lakes, rivers,) from cold air

Fig. 3-6 Hydrogen bond Liquid water Hydrogen bonds break and re-form Ice Hydrogen bonds are stable

SOLUTIONS  3 parts  Solution – mixture of substances that is uniform throughout  Solvent – substance in the greatest amount that dissolves something else (like water)  Solute – the substance that dissolves  What are the parts in a can of soda?

ACIDS AND BASES  Since substances sometimes break down into ions in water, we can have some free floating protons in a solution  Higher amount of protons = acid  Lower amounts of protons = base  Strongest acid = zero on the pH scale.  Strongest base = 14 on the pH scale.  The closer a substance gets to the number 7 on the scale, the more neutral (or less reactive) it becomes.

Fig More acidic 0 Acid rain Acid rain Normal rain More basic