1 the nature of molecules chapter 3. 2 water chemistry water consists of an oxygen atom bound to two...
TRANSCRIPT
1
The Nature of Molecules
Chapter 3
2
Water Chemistry
• Water consists of an oxygen atom bound to two hydrogen atoms by two single covalent bonds.
– stable atom with no electrical charge most outstanding property is its ability to
form weak chemical associations
3
Hydrogen Bonding
• In a water molecule, both the oxygen and hydrogen atoms attract the shared electrons in the covalent bond
– Oxygen atom is more negative than the hydrogen atoms.
distinct ends with partial charge (polar)hydrogen bonds
4
Water Chemistry
• Water clings to polar molecules.– Cohesion refers to attraction
to other water molecules. responsible for surface
tension: water strider leaves can pull water up
the stem Seeds swell to germinate
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–Adhesion refers to attraction to other substances.
Water is adhesive to any other substance with which it can form hydrogen bonds.
Capillary action on glass
6
Water Chemistry
•Water is an effective solvent as it can form hydrogen bonds.
–Water clings to polar molecules causing them to be soluble in water.
Hydrophilic - attracted to water( sugar/salt)
–Water tends to exclude nonpolar molecules.
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WatermoleculesSalt
crystal
Na+
Cl–
Cl–
Na+
Na+
Na+
Cl–
Cl–
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Hydrophobic - repelled by water-form their own layer
Water and oil do not mix !
9
pH
• pH scale expresses hydrogen ion (H+) concentration in a solution.
– logarithmic scale ranging from 0-14 neutral = 7
10
pH
• Acids dissociate in water to increase the concentration of H+.
– pH values lower than 7
• Bases combine with H+ ions when dissolved in water, thus decreasing H+ concentration.
– pH values above 7
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pH
Neutral
MoreH ion
LessH ion OH
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How Acid and bases affect the homeostasis of our bodies
CO 2 is acidic: high levels in blood will send message back to brain to breathe faster: remove CO2 and return to normal pH
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