1. The Properties of Water

3. Remember… A molecule often consists of atoms bonded COVALENTLY!
Covalent bonds occur when atoms share electrons
Circle which electrons are being shared

4. Polarity Seen in molecules, which are often bonded covalently!
Occurs when the shared electrons are attracted more strongly to one atom than to the other
As a result, one end, or pole, of the molecule has a partial negative charge while the opposite side has a partial positive charge
These types of molecules are POLAR

5. Polarity Negative Pole Positive Pole
The pole with more electrons is more NEGATIVE
The pole with fewer electrons is more POSITIVE
Which pole is which in this diagram?
Positive Pole

6. Hydrogen Bonds
Polarity allows water molecules to be bonded together by hydrogen bonds
A hydrogen bond is when a slightly positive hydrogen bonds to a slightly negative oxygen (or nitrogen or fluorine)

7. Solubility
The partially charged ends of polar molecules attract opposite charges
Because of this, water can dissolve other polar substances (like sugar and salt)
Non-polar substances (like oil) don’t dissolve in water!
LIKE DISSOLVES LIKE!

8. Properties of Water 1. Water is less dense as a solid than as a liquid
When water freezes, hydrogen bonds lock water molecules into a crystal structure that has empty spaces, so ice floats!
Why is this beneficial?
Floating ice prevents rivers, lakes, and oceans from freezing solid, so life can exist in the water under the ice.

9. Properties of Water 2. Water absorbs and retains heat well
It takes a lot of energy to heat or cool water
Why is this beneficial?
Large bodies of water can help keep temperatures on Earth from changing too fast.

10. Properties of Water 3. Water molecules stick to each other
Hydrogen bonds hold water molecules together, so that small drops are pulled into a ball shape (aka surface tension)
Cohesion is when particles of the same substance are attracted to each other
Why is this beneficial?
Prevents massive evaporation

11. Properties of Water 4. Water molecules stick to other substances
Adhesion is when particles of different substances are attracted to each other
Why is this beneficial?

12. Solutions
Many substances are transported through living things as solutions of water
A solution is a mixture in which one substance is evenly distributed in another substance
A solute dissolves in a solvent to make a solution