Introduction to Water

Created by Dr. Michael Pidwirny, Department of Geography, Okanagan University College, BC, CA evaporation Soil and Water

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 % of the human body

105 0 Oxygen Hydrogen Electro positive Negative Polarity Symmetrical (e.g., CO2) H-O : 0.97 A H-H : 1.54 A angstroms

H+H+ H+H+ O -- = + - H2OH2O Hydrogen bond 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

O= H+H+ H+H+ Polymer type of grouping Cations: Na +, K +, Ca 2+ 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), (2004).

Does water swell and shrink with Temperature? Density (g cm -3 ) Temperature ( 0 C) 40C40C

www-ssrl.slac.stanford.edu/.../structure_ice.jpg purves6/figure02-15a.jpg

Representation of Ice Melting

periods groups Dimitri Mendeleev

Temperature range in liquid phase for H 2 x compounds Molecular Weight Temperature ( 0 C) 100 H2OH2O H2SH2S H 2 Se H 2 Te Boiling point Freezing point Hydrogen sulfide Hydrogen selenide Hydrogen telluride (2+16=18) (2+32=34) (80) (130) 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?

www2.mcdaniel.edu/.../botf99/nutrition/soils.htm

Clay minerals as sources of ions

Typical ion concentrations (can be much higher in arid regions due to high evapotranspiration (ET) and concentrating effects) K (mg/L) Na Ca Mg Si SO Cl

Solutes exist in solution as: Free hydrated ions Complexes with ligands organic or inorganic (H 2 O, NH 3 +, F -, OH -, Cl -, CN - or EDTA, citric acid, DTPA, NTA,…)

“Free” hydrated ions

Metal-ligand complexes

Ligand Exchange Mechanisms [ ML 6 + Y -  ML 5 Y + L - ]