1. Water
© 2016 Paul Billiet ODWS

2. Formula H2O Structure Slightly () negative at the oxygen end and slightly positive at the hydrogen end. - + O H
© 2016 Paul Billiet ODWS

3. The association between the polar water molecules
Weak hydrogen bonds
© 2016 Paul Billiet ODWS

4. Comparing molecules
Boiling point
/ °C
Melting point
Molecular mass
Formula
Molecule
-161
-184 16
CH4
Methane
-33
-78 17
NH3
Ammonia
+100 18
H2O
Water
+19
-92 20 HF
Hydrogen fluoride
-61
-86 34
H2S
Hydrogen sulphide
Compared to molecules of similar size and properties water has a very high melting point and boiling point.
© 2016 Paul Billiet ODWS

5. Polar properties of water and methaneC H - + O H
© 2016 Paul Billiet ODWS

6. Thermal properties
The molecules of water can absorb a lot of heat energy
Water has a very high thermal capacity (4.2 J°C-1 g-1)
The hydrogen bonding forms a lattice which does not easily fall apart as the temperature rises.
© 2016 Paul Billiet ODWS

7. Thermal properties of water and life
Very thermally stable medium
Helps living organisms resist changes in their environment
To make water change from a liquid to a vapour requires a lot of energy
Evaporation of water on the surface of a body cools it down significantly.
© 2016 Paul Billiet ODWS

8. Indian elephant (Elephas maximus indicus) bathing
© 2016 Paul Billiet ODWS

9. Solvent properties
The polar properties of water make it a good solvent for:
Polar molecules (e.g. sugars and alcohols)
form hydrogen bonds with the water molecules
Ionic compounds (e.g. salts. acids and bases)
dissociate into their component ions e.g. NaCl Na+ + Cl-
© 2016 Paul Billiet ODWS

10. Solvent properties of water and life
A very important transport medium for living organisms
because of its solvent properties and…
because it remains a liquid over a large range of temperatures
Also an important medium for biochemical reactions.
© 2016 Paul Billiet ODWS

11. webvision.med.utah.edu/imageswv/FlorretBV.jpg
© 2016 Paul Billiet ODWS

12. Cohesion The cohesion (stickiness) between water molecules
Water molecules are also attracted to wettable surfaces
Very tall thin columns of water can be supported before they break
The tallest are at the physical limits of water trees (sequoia and eucalyptus are 100m tall).
© 2016 Paul Billiet ODWS

13. Giant red wood Sequoiadendron giganteum
California USA
Eucalyptus grandis
NSW Australia
homepage.mac.com/.../Redwood/rw-002.jpg
© 2016 Paul Billiet ODWS

14. Surface tension
Water molecules hold together forming a skin at the surface
This is strong enough for some organisms to be supported.
Raft spider
Dolomedes fimbriatus
i1.treknature.com/photos/12/p a_nibts1.jpg
© 2016 Paul Billiet ODWS