H₂O

covalently bonded - relatively strong bonds
105^o angle separates the H atoms - causes most of the unique properties of water

polarity

the bent geometry gives a slight negative charge to the O atom and a slight positive charge to the H atom; the slight separation of charges give the molecule electrical polarity; water is bipolar

water molecules are interconnected to each other by H bonds; these are weaker bonds, but are strong enough to stick to one another and exhibit cohesion (surface tension - results from the bond between the outer most layer of water molecules and the underlying water molecules; highest surface tension with the exception of mercury)

solvent and solutes

bond with other polar compounds

e.g. NaCl - bonded by ionic bonds (electrostatic attraction); when NaCl is placed in water, the ionic bond is reduced by 80x; NaCl is separated into Na ions which are attracted to the negatively charged O and Cl ions which are attracted to the positively charged H and NaCl is dissolved; hydration - process by which water molecules completely surround ions

given enough time, water can dissolve more substances and in greater quantity than any other known substance; called the universal solvent; why the ocean contains so much dissolved material

hydrophobic vs. hydrophylic

water thermal properties

latent heat - heat released or absorbed during a change in state from gas to liquid to solid and solid to liquid to gas, respectively; heat energy to overcome is H bonds and van der Waals forces (attractive forces when molecules are close together; like ice and water)
- latent heat of melting
- latent heat of vaporization
- latent heat of evaporation
- latent heat of condensation
- latent heat of freezing

e.g.  latent heat of evaporation and condensation transfers the heat energy from the oceans to the atmosphere moderating the earth's climate
e.g. same principles used when ice is added to a cooler

heat capacity - amount of heat required to raise the temperature of 1 g of any substance by 1 degree Celsius; water has a high heat capacity (1 calorie per gram), while oil and metals have low heat capacities
- why water is used in home heating and cooling systems
- causes less temperature fluctuations at the coasts than inland

water density

the density of water is 1 g/ml

thermal contraction - as water cools its density increases (the amount of motion decreases so the water molecules occupy less space); from 4^o C to 1^o C however, its density increases because ice crystals form requiring more space (volume increases about 9%); result is that ice is less dense than water and floats; increasing the pressure or adding dissolved substances (inhibits the formation of H bonds) decreases the freezing temperature because the formation of bulky ice crystals is inhibited - reason most seawater never freezes, except at the poles
 

Seawater

salinity
total amount of material dissolved in water; does not include the fine particles held in suspension - turbidity; 3.5 % or 220x more saltier than freshwater; chlorine (55%), sodium (31%), sulfur (sulfate ion - 8%), magnesium (4%), calcium (1%) and potassium (1%) account for 99% of the salinity; at least 89 other chemical elements have been identified in trace amounts as part of the salinity

or give in ppt (parts per thousand); advantage of ppt is that avoids the decimal and values convert directly to grams of salt per kilogram of seawater
- 35 ppt

in open ocean salinity varies from 33-38 ppt; wide variations:
- hypersaline water: due to high evaporation rates (seasonal) and limited open ocean circulation; e.g. Red sea - averages 42 ppt; most found in inland lakes: e.g. Great Salt Lake - 280 ppt and Dead Sea - 330 ppt; so dense that one can easily float
- brackish water - produced when fresh water and seawater mix (seasonal); in coastal areas, salinity variation can be extreme; e.g. Baltic sea - averages 10 ppt
- tap water - less than 0.8 ppt
- bottled water - less than 0.3 ppt; often displayed as TDS (total dissolved solids)

dissolved components

input - volcanic eruptions (mostly anions; e.g. Cl^-, SO₄^2-); stream erosion (mostly cations; e.g. Ca²⁺, Na⁺, Mg ²⁺, K⁺)
^{output - release into atmosphere or over land in the form of salt spray; infiltration of freshwater; uptake by aquatic organisms; absorption to organic matter and settling}

^{acidity and alkalinity of seawater}

acid - H⁺
base - OH^-

H₂O <-> H⁺ + OH^-

dissociate ->
reform <-

carbonate buffering system

CaCO₃ comes from the sediment deposits and dead aquatic organisms