Water and its Properties

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Water and its Properties

• Chapter 2
• Section 2.3

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Life requires 25 chemical elements

• Four elements make up 96 of living matter
• _______________ ______________
• _______________ ______________
• Four elements make up most of remaining 4
• phosphorus (P) calcium (Ca)
• sulfur (S) potassium (K)

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Bonding properties

• Effect of electrons
• electrons determine chemical behavior of atom
• depends on numberof electrons in atoms
  outermost shell
• valence shell

How does this atom behave?
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How do these atoms behave?
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Chemical reactivity

• Atoms tend to
• complete a partially filled valence shell
• or
• empty a partially filled valence shell

This tendency drives chemical reactions
and creates bonds
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Important Bonds in Biology
Hydrogen bond

• Weak bonds
• hydrogen bonds
• attraction between and
• hydrophobic hydrophilic interactions
• interaction with H2O
• van derWaals forces
• Strong bonds
• ionic
• covalent bonds

H2O
H2O
Covalent bond
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Polarity

• Highly electronegative molecules (O, F, N) have
  the ability to pull electrons toward them

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Polarity of Water
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Hydrogen Bonding of H2O

• How many hydrogen bonds can water make?

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Emergent Properties of Water due to H-bonding

• High heat capacity
• Requires lots of energy to raise temp
• High heat of vaporization
• Requires lots of energy to evaporate
• Good solvent

• Ability for adhesion
• Ability for cohesion
• High surface tension
• Requires lots of energy to break molecules apart

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Adhesion vs. Cohesion

• ADHESION
• H bonding between H2O other substances

• COHESION
• H bonding between H2O molecules

Identify the adhesion and cohesion appearing in
the following image.
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Solutions

• Water is a great SOLVENT (dissolver)
• Its polarity attracts charged atoms and breaks
  them into their smallest parts

WHY?
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Solutions

• Water ionizes (breaks down) as shown below
• Solutions with many hydronium (H30 or H) are
  ACIDIC
• Solutions with many hydroxide (OH-) are BASIC

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Solutions

• pH is a measurement of how many hydrogen ions are
  in the solution

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pH Scale
tenfold changein H ions pH1 ? pH2 10-1 ?
10-2 10 times less H pH8 ? pH7 10-8 ? 10-7 10
times more H pH10 ? pH8 10-10 ? 10-8 100 times
more H
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Buffers cellular regulation

• pH of cells must be kept 7
• pH affects shape of molecules
• shape of molecules affect function
• pH affects cellular function
• Control pH by buffers
• reservoir of H
• donate H when H falls
• absorb H when H rises

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Buffer Example

• Blood
• Must stay around 7.4 or body may go into a state
  of acidosis or alkalosis
• Has bicarbonate (H2CO3) in it
• H2CO3 lt-----gt H HCO3-
• If blood is too acidic, HCO3- absorbs H
• Too basic H2CO3 breaks down