1. WATER http://www.youtube.com/watch?v=HW5eBfZhE4M

2. • Water molecules form because neither the H or the O atom has a filled outer (valance) shell of electrons
• By sharing electrons via covalent bonds, all the atoms become stable.
• However, since oxygen has more positive particles in its atomic nucleus, the electrons are more attracted to; it is more electronegative than hydrogen
A Water Molecule

3. • This unequal distribution of electrons makes water a polar molecule
• Polar molecules have regions with a partial positive charge, and regions with a partial negative charge
• a water molecule thus behaves like a weak dipole magnet
640::480::/sites/dl/free/ /811313/Polarity.mov::Polarity

4. • These hydrogen bonds between molecules make water cohesive
• Because opposite charges attract, water molecules form bonds with other water molecules, positive H to negative O.
• These hydrogen bonds between molecules make water cohesive

5. Cohesion between adjacent molecules is strongest at the surface, creating surface tension

6. Water also forms H bonds with other charged molecules and ions
This is called adhesion; these substances are hydrophillic
creates the meniscus in a glass test tube
causes water to climb up small tubes in capillary action

7. Molecules that share electrons equally between atoms are not charged and do not form H bonds are non-polar
Non-polar substances are hydrophobic – they do not mix with water

8. Hydroxide ion OH- Hydrogen ion H+
• In pure H2O, a few water molecules will spontaneously break apart, creating charged particles, called ions
•the ‘free’ H donates its e- to the OH
• thus, a H ion is just a proton!
Anode +ve 6H2O(l)  > O2(g) + 4H3O+(aq) + 4e-(to anode)
Cathode -ve 4e-(from cathode) + 4H2O(l) >  2H2(g) + 4OH-(aq
Overall 2H2O(l) > 2H2(g) + O2(g)
Hydroxide ion
OH-
Hydrogen ion H+

9. • Pure water has a 1:1 ratio of H+:OH-, and so the pH is neutral at 7.
• The ratio of these charged particles determines a solutions pH (percent hydrogen)
• Pure water has a 1:1 ratio of H+:OH-, and so the pH is neutral at 7.
acidic sol’ns neutral basic sol’ns
more H equal H+/OH more OH- H+ H+ H+ H+ H+ H+ H+
H H+ H+ H+ H+ H+ H+ H+
OH- H+ H+ H+ H+
OH- H+ H+ H+ H+
OH- H+ H+ H+ H+ H+
OH- H+
OH-
OH-
OH- H+ H+
OH-
OH- H+
OH-
OH-
OH- H+
OH-
OH-
OH- OH-
OH-
OH-
OH-
OH- OH-
OH-
OH-
OH-

11. So….water is polar, therefore it is…
is Cohesive
forming hydrogen bonds with other water molecules
water drops, surface tension
is Adhesive
forms hydrogen bonds with other polar and charged molecules
absorption, test tube meniscus, glass plates stick together
Does NOT form bonds with non-polar molecules
‘balls up’ on plastic sheet, waxy surfaces, oily pans
SO WHAT?

12. 1. Water has a high specific heat
• Raising it’s temperature requires breaking lots of
H-bonds; lots of energy required
• Therefore water warms slowly, cools slowly
Brooks
Inst of Photo.
Claremont
Colleges
Univ. of
Redlands
70 F
80F
90F
100F
little coastal cooling
• example: relatively constant
ocean temperature
regulates coastal climate
USD

13. • example: high water content of organisms results in a stable internal temp
Water in cells doesn’t freeze! Water in cells doesn’t boil!

14. 2. Water has a high heat of vaporization
changing state from liquid to gas takes energy
example:
• heat from body evaporates sweat on skin; cooling effect

15. • ex: from the roots to leaves in plants
3. Water is transported via capillary action
• employs both cohesion & adhesion
• ex: from the roots to leaves in plants
for photosynthesis, transpiration
The researchers further found that those phalaropes with a ‘bumpier’ mouth terrain needed less ‘rachets’ to move the water/food up the beak
• ex: Phalarope beaks have a bumpy interior that allows for the quick uptake of a drop of food-containing water
MIT beak model

16. 4. Polar/charged molecules and ions dissolve in water, creating solutions
• Water is the solvent; charged solutes dissolve in it
• ex: in water, the hydrophillic NaCl molecule dissociates into the ions* Na+ and Cl-, creating a solution
NaCl salt crystal
*an atom with an unequal number of p+ and e- particles

17. Some solutes change the ratio of hydrogen (H)+ to hydroxide (OH-) ions when dissolved in water
• This changes waters pH
more H equal H+: OH more OH-

18. Acid solutes - like HCl – donate H+ to the solution
HCl molecules
water
Acid solutes - like HCl – donate H+ to the solution
• lowers the pH
• makes the sol’n acidic
• H+ is a hydrogen ion;
shorthand for H3O+

19. Basic solutes - like NaOH –donate OH- (hydroxide) ions
water
Basic solutes - like NaOH –donate OH- (hydroxide) ions
• raises the pH
• make the sol’n a base

20. So what?
pH changes disrupt molecules, affecting interactions within & between molecules
• example:
breaks down proteins breaks down fats

21. 5. Solid water - ice - is less dense than liquid form
• cold air at surface
• top freezes first; ice floats
• depth remains ice-free
(• high specific heat)
• aquatic life survives!
solid (ice) liquid (water)
a frozen Minnesota lake