Introduction to Water
Soil and Water
evaporation
Created by Dr. Michael Pidwirny, Department of
Geography, Okanagan University College, BC, CA
What is Soil?
The interface between the atmosphere,
hydrosphere, biosphere and lithosphere
naturally occurring layers of mineral and
organic constituents that differ from the
underlying parent material in their physical,
chemical, and mineralogical properties
Rock
What is Water?
A binary compound that occurs at room temperature as a
clear colorless, odorless, tasteless liquid
Freezes into ice below 0 C and boils above 100 C
Necessary for life on earth (human, animals and plants)
Constitutes 60-70 % of the human body
www.atpm.com
Hydrogen
Electro positive
Hydrogen
H-O : 0.97 A
1050
H-H : 1.54 A
Polarity
Oxygen
angstroms
Negative
Symmetrical
(e.g., CO2)
Hydrogen bond
H+
H2O
=
O--
+
-
H+
Gives structural strength
Bond depends on temperature:
Bonds are weaker at higher temperature
Positive end attraction with neg. end of other water molecules
Dipolar nature of water due to
unevenly distributed charges
http://www.chem1.com/acad/sci/aboutwater.html
Polymer type of grouping
H+
H+
O=
Cations: Na+, K+, Ca2+ become hydrated through their
attraction to the negative end of water (Oxygen side)
Anions or negatively charged clay surfaces attract water
through positive hydrogen side
J. L. Fulton, Y. Chen, S. M. Heald, and M. Balasubramanian,
Rev. Sci. Instruments., 75(12), 5228-5231 (2004).
http://www.pnl.gov/cmsd/highlights/images/20050727water.jpg
http://courses.cm.utexas.edu/jrobertus/ch339k/overheads-1/water-structure.jpg
Does water swell and shrink with Temperature?
1
0.998
40 C
0.996
Density (g cm-3)
0.994
0.992
0.990
Temperature (0C)
-10
0
10
20
30
40
50
http://www.columbia.edu/cu/biology/courses/c2005/
purves6/figure02-15a.jpg
www-ssrl.slac.stanford.edu/.../structure_ice.jpg
Representation of Ice Melting
www.cscs.ch/.../representations/index.html
groups
periods
Dimitri Mendeleev
Temperature range in liquid phase for H2x compounds
100
Boiling point
Freezing point
H2O (2+16=18)
Temperature (0C)
50
Hydrogen telluride
0
H2Te
Hydrogen sulfide
-50
H 2S
H2Se
(130)
(80)
Hydrogen selenide
(2+32=34)
-100
0
50
100
Molecular Weight
The sum of the atomic weights of all atoms in a molecule
If water were an ordinary compound whose molecules are
subject to weak forces, its boiling and freezing points
would fall below hydrogen sulfide
Strong hydrogen bonding between water molecules
prevents this so that liquid water acts more like a gel,
cluster, or polymer
Water occurs in all three states (solid, liquid, and gaseous)
at prevailing temperatures on the earth’s surface
Example: Ice cubes in a glass at room temperature
Soil Solution
aqueous liquid phase of the soil
and its solutes
Hydrogen Bonding
Water is a powerful solvent
How salt dissolves in water
nutrition.jbpub.com/.../chemistryreview6.cfm
How do plants obtain the
nutrients in the soil?
http://www2.mcdaniel.edu/Biology/botf99/nutrition/catex.jpg
www2.mcdaniel.edu/.../botf99/nutrition/soils.htm
Clay minerals as sources of ions
http://www.ca.uky.edu/agc/pubs/agr/agr11/fff00003.gif
Typical ion concentrations
(can be much higher in arid regions due to high
evapotranspiration (ET) and concentrating effects)
K+ 1-10 (mg/L)
Na+ 1-5
Ca+2 20-200
Mg+2 2-50
Si+4 10-50
SO4-2 60-300
Cl- 50-500
Solutes exist in solution as:
• Free hydrated ions
• Complexes with ligands
organic or inorganic
(H2O, NH3+, F-, OH-, Cl-, CN- or
EDTA, citric acid, DTPA, NTA,…)
“Free” hydrated ions
Metal-ligand complexes
http://www.freepatentsonline.com/7115549-0-large.jpg
http://journals.iucr.org/e/issues/2006/11/00/ng2089/ng2089scheme1.gif
Ligand Exchange Mechanisms
[ ML6 + Y-  ML5Y + L- ]
www.meta-synthesis.com/.../mechanism.html