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Chemical Foundations for Cells

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Properties of Water. Water has a high surface tension can also say, water is cohesive. ... Proteins function only at specific pHs. ... – PowerPoint PPT presentation

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Title: Chemical Foundations for Cells


1
Chapter 2
  • Chemical Foundations for Cells

2
Chapter Outline
  • Review of atomic structure
  • Chemical bonding
  • Ionic
  • Covalent nonpolar and polar
  • Hydrogen bonding
  • Properties of water
  • Acids, bases, and buffers

3
Atomic Structure
  • Nucleus contains ____________
  • Electrons are found outside of the nucleus
  • In an atom the of protons electrons
  • Some electron arrangements are more stable than
    others.

4
Chemical Bonding
  • Chemical bonding atoms gain, lose, or share
    electron(s) to obtain a stable number of electrons

5
Chemical Bonding
  • There are two types of bonds
  • Ionic bonds
  • Covalent bonds
  • May be polar or nonpolar

6
Chemical Bonding
  • Ionic Bond strong attractive force between
    oppositely charged ions
  • Atoms form ions by losing or gaining enough
    electron(s) to obtain a stable of electrons in
    their outer shell

7
Chemical Bonding
  • Terms
  • Cation Positive ion, formed when an atom ____
    electron(s)
  • Anion - Negative ion, formed when an atom ____
    electron(s)

8
Chemical Bonding
  • Covalent Bond bonded atoms share pair(s) of
    electrons.
  • Occurs between ___________
  • Examples
  • H2
  • O2
  • H2 O

9
Types of Covalent Bonds
  • Nonpolar covalent bonded atoms share the
    electrons equally
  • Examples
  • Polar Covalent unequal pull on shared electrons
    by the bonded atoms
  • Examples

10
Hydrogen Bonding
  • Hydrogen bond weak attractive force between a
    d hydrogen bonded to an O, N or F atom and a d-
    O, N, or F in a second polar bond
  • Examples
  • A hydrogen bond is not a true bond.

11
Properties of Water
  • Water is a polar molecule capable of hydrogen
    bonding.
  • Related Terms
  • Hydrophilic
  • Hydrophobic

12
Properties of Water
  • Water resists changes in temperature.
  • When heat is applied to an aqueous solution much
    of the heat (energy) is used to break hydrogen
    bonds, not increase the movement of the molecules.

13
Properties of Water
  • Water has a high surface tension can also say,
    water is cohesive.
  • Cohesion ability to resist rupturing when under
    tension

14
Properties of Water
  • Water is a good solvent for ionic compounds and
    small polar molecules.
  • Water hydrates ions
  • Water hydrogen bonds to polar molecules

15
Acids, Base, and Buffers
  • Many ions are dissolved in the fluids in/outside
    of cells
  • Na, Ca2, K,
  • H
  • Level of each is critical
  • Focus on H (hydrogen ions)

16
Acids, Base, and Buffers
  • Use the pH scale as a measure of the
    concentration of H in dilute solutions
  • See page 28
  • Classify substances as acid, base or neutral by
    their pH
  • Acids pH lt 7
  • Base pH gt 7
  • Neutral pH 7

17
Acids, Base, and Buffers
  • How the pH scale works
  • The lower the pH the more acidic
  • The higher the pH the more basic (alkaline)
  • A difference of 1 pH unit is a 10-fold difference
    in acidity or alkalinity

18
Acids, Base, and Buffers
  • Acid Substance that produces H when dissolved
    in water.
  • Properties of Acids
  • Corrosive
  • Sour if dilute enough to drink
  • Neutralize bases

19
Acids, Base, and Buffers
  • Classifying Acids
  • Strong acids ionize completely in water
  • Every acid molecule ionizes to form H
  • Example
  • Weak Acids ionize slightly in water
  • Very few acid molecules form H in water
  • Examples

20
Acids, Base, and Buffers
  • Base substance that produces OH-1 (hydroxide
    ion) in water
  • Examples
  • Properties of bases
  • Corrosive
  • Bitter if dilute enough to drink
  • Neutralize acids

21
Why is pH important?
  • Most cells require a pH near 7. Above or below
    this pH for too long and they die.

22
Why is pH important?
  • Proteins function only at specific pHs.
  • pH needed depends upon where the protein needs to
    function
  • In lab you will determine the optimal pH for a
    protein that acts as an enzyme.

23
Why is pH important?
  • Blood has a pH of 7.3 7.5
  • If the pH is above or below this range for more
    than a couple of days death occurs.

a little higher than most give for the pH of
blood
24
Acids, Base, and Buffers
  • Buffers solution that resists changes in pH
    even when acid or base is added
  • Buffers can both produce H and neutralize H
  • Most body solutions are buffered

25
Buffers
  • Buffers are key to maintaining pH homeostasis
  • Buffers are made from weak acids and the ions
    they form in water
  • Ions formed act as bases in that they can
    neutralize (bind) H

26
Buffers
  • Blood buffer system see board and page 29

27
Salts
  • Salts are ionic compounds that do not produce H
    or OH-1 when dissolved in water
  • Salt solutions are neutral
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