Water and Diffusion Sect. 6.2

1. Water and DiffusionSect. 6.2 1. ---Water and it’s importance 2. ---Diffusion

2. Polar covalent bonds – covalent bond • when electrons are shared unequally. • Polar Molecule - having slight positive • and negative charges on the molecule • Ex. Water or

3. --all of water’s properties are due to water molecules being polar. Water and Its Importance 1. each Oxygen atom has a slight negative charge(-) 2. each Hydrogen atom has a slight positive charge (+) --the charges can attract other charged particles that are in the water!!!

4. Oxygen (blue) – slight negative charge Hydrogens (red) – slight positive charges

5. --A Polar water molecule can form weak, short lived Hydrogen Bonds with other water molecules that break quickly and reform quickly. --Hydrogen Bonds can also form between water and other charged compounds!!

6. Hydrogen bonding in water animation!!

7. Special Properties of Water (due to hydrogen bonds!!) 1. Water dissolves substances with ionic bonds ex. -- Sugar, salt and other polar liquids The water molecules form water cages around the charged ions.

8. 2. Water molecules have cohesion (stick together): -surface tension – hydrogen bonds between water molecules allow the surface molecules to support weight ex. – water bugs or forming drops on glass Surface Tension Movie

9. -Capillary action – ability of moving water molecules to pull other waters along 1. Evaporating water from plant leaves pulls water up from the soil (transpiration). 2. Meniscus formation when measuring water in a glass graduated cylinder.

10. 3. Water resists temperature change Ex. --cooling effect of sweating --As a coolant in combustion engines --water to evaporate or boil --moderates the climate a. absorbs heat in summer b. releases heat when it cools

11. 4. Water expands when it freezes --Hydrogen bonds between water molecules do not break and hold the molecules in place forming crystals Normal water forming and breaking hydrogen bonds Water in a frozen crystal shape. --hydrogen bonds form but do not break --Note the increased space between the molecules

12. Diffusion – net movement of particles from an area of higherconcentration. to an area of lowerconcentration. -the movement is due to the random movement of molecules called Brownian movement. -diffusion does not cost the cell any energy

13. Result of diffusion : Dynamic Equilibrium: -equal concentration of materials has occurred -continuous movement occurs but no net change Rate of diffusion: depends on and can be changed by: 1. Temperature 2. Concentration gradient 3. Pressure