1. Chemistry of Water Chapter 2.4
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2. Outline Chemistry of Water Properties of Water pH Scale
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3. Living Things are Mostly Water
Each cell is approximately 70% water
Water is essential to life because of its unique properties
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4. Structure of Water The water molecule is simple and stable
Covalent bonds
Octet rule satisfied
One oxygen atom bound to two hydrogen atoms by two single covalent bonds.
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5. Properties of Water
Most important quality is ability to form weak chemical associations due to polarity
Oxygen is more electronegative than Hydrogen and pulls electrons more strongly
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6. Polar Molecule - Has distinct ends, each with a partial charge.
Hydrogen Bonds
In a water molecule, both oxygen and hydrogen atoms attract shared electrons in the covalent bonds (electronegativity).
Shared electrons are thus more likely to be found near the oxygen nucleus than near the hydrogen nuclei.
Polar Molecule - Has distinct ends, each with a partial charge.
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7. Properties of Water
Polarity of water causes it to be attracted to other polar molecules.
Cohesion - Attraction to other water molecules.
Responsible for surface tension.
Reason why water is a liquid at Earth’s temperatures
Ex: As transpiration occurs from leaf surface, water is pulled up the xylem from the roots.
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8. Properties of Water
Polarity of water causes it to be attracted to other polar molecules.
Adhesion - Attraction to other substance.
Capillary action also helps water move up the xylem
More narrow tube, the greater the electrostatic forces between water and the wall of the tube
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9. Water Moderates Temperature
Heat Storage - Because of the large number of hydrogen bonds, a large input of thermal energy is necessary to break apart water molecules.
High Specific Heat -amount of energy needed to allow molecules to break free (break H-bonds) & increase in temperature
Amount of energy required to raise 1g of a substance by 1oC
Water = 1calorie/g/oC
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10. Water Moderates Temperature
High Heat of Vaporization (energy required to change liquid water to gas)
Water = 586 cal/g
Because energy is required to break H-bonds to cause vaporization, evaporation of water has a cooling effect on the surface from which it evaporates
Ex: sweating cools your body
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11. Ice is less dense than liquid water due to the lattice
Properties of Water
At low temperatures, water molecules form a crystal-like lattice of H-bonds forming ice
Ice is less dense than liquid water due to the lattice
Thus, ice floats.
Otherwise, inland bodies of water far from equator may stay solid year-round
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12. Ex: NaCl forms ions as it dissolves (quickly)
Properties of Water
Solvent - Water is an effective solvent because of its ability to form hydrogen bonds.
Water molecules gather around any substance bearing an electrical charge.
Ex: NaCl forms ions as it dissolves (quickly)
Ex: sugar has polar –OH groups (doesn’t dissolve as fast as salt)
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14. Hydrophobic - Nonpolar molecules shrink from contact with water.
Properties of Water
Organization of Nonpolar Molecules - Water molecules act to exclude nonpolar molecules.
Hydrophobic - Nonpolar molecules shrink from contact with water.
(Water Hating)
Hydrophilic - Polar molecules readily form hydrogen bonds with water.
(Water Loving)
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15. Ionization - Spontaneous ion formation.
Water Ionizes
Ionization - Spontaneous ion formation.
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16. Bases - Substances that combines with H+ ions when dissolved in water.
Water Ionizes
pH Scale - Measures negative logarithm of hydrogen ion concentration in the solution.
Acids - Substances that dissociate in water to increase concentration of H+ ions.
pH values below 7.
Bases - Substances that combines with H+ ions when dissolved in water.
pH values above 7.
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17. Raven - Johnson - Biology: 6th Ed
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18. Water Ionizes Ex: Carbonic acid and bicarbonate (base)
Buffer - A substance that acts as a reservoir for hydrogen atoms.
Donates hydrogen atoms to solution when concentration falls, and removes them from the solution when concentration rises.
Minimize change in pH.
Ex: Carbonic acid and bicarbonate (base)
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19. Review Atoms Basic Structure Chemical Behavior Ionic Bonds
Covalent Bonds
Hydrogen Bonds
Chemistry of Water
Properties of Water
pH Scale
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20. Copyright © McGraw-Hill Companies Permission required for reproduction or display
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