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AP Biology�Unit 1 Notes: �Biochemistry & �Properties of Water

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(1) Matter

  • Atoms are the basic units of matter:�
    • Protons 🡪 Positively Charged ; Located in Nucleus ; 1amu�
    • Neutrons 🡪 Neutral (No Charge) ; Located in Nucleus ; 1amu�
    • Electrons 🡪 Negatively Charged ; In Orbitals Around Nucleus ; 0amu

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  • Atomic Number = # of Protons
  • Atomic Mass = #Protons + # Neutrons
  • Average Atomic Weight = Average of the element’s isotopes’ masses

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  • Ions are charged atoms:�
    • Atoms will naturally gain / lose valence electrons in their outer orbital in order to gain stability.�
    • Cations 🡪 Positively Charged Atoms (due to LOSS of electron/s)�
    • Anions 🡪 Negatively Charged Ions (due to GAIN of electron/s)�
    • The interaction of valence electrons between atoms, determines chemical reactivity.

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  • Isotopes are atoms of an element with a different number of Neutrons:�
    • Same element�
    • Different # of Neutrons ; Different Mass ; �Chemically the same (Electrons do not change)�
    • Some Isotopes Decay (break down through nuclear fusion), not all.

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(2) Bonds

  • A Chemical Bond is the interaction between the valence electrons of different atoms:�
    • Ionic Bond 🡪 Valence electrons are TRANSFERRED from one atom to another.�
    • Covalent Bond 🡪 Valence electrons SHARED between atoms (only in MOLECULES).�
      • Single Covalent Bond = 2 Valence Electrons / 1 Pair Shared
      • Double Covalent Bond = 4 Valence Electrons / 2 Pairs Shared
      • Triple Covalent Bond = 6 Valence Electrons / 3 Pairs Shared

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  • Types of Covalent Bonds:�
    • Polar Covalent 🡪 When electrons are shared unequally, in the bond, between atoms. (The O and C bonds in CO2)�
    • Nonpolar Covalent 🡪 When electrons are shared equally, in the bond, between atoms. (Diatomic Molecules like H2, O2, N2, Cl2)���
  • An Intermolecular Bond exists between molecules/compounds, and results from natural attractive forces between compounds.

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(3) Polarity

  • Polar: When electrons are unevenly shared between atoms, resulting in an uneven distribution of charge across a molecule.�
    • One end of the MOLECULE is more positively charged than the other. �
    • Larger Atoms = Stronger Electronegativity = Greater Pull on Electrons �= More Negatively Charged�
    • Smaller Atoms = Weaker Electronegativity = Barely Pulls on Electrons �= More Positively Charged

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(4) Water Chemistry

  • Water = H2O = 2 Hs + 1 O�
    • Polar Covalent Chemical Bonds�
    • Hydrogen Intermolecular Bonds (Opposing Charges Attracted)�
    • Polar Molecule = Polar Substance�
    • Oxygen Atom is larger 🡪 Pulls on Electrons = Negatively charged�
    • Hydrogen Atoms are smaller = Positively charged

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  • Hydrophilic = Water Loving�
  • Hydrophobic = Water Fearing�
  • Only Polar + Ionic Substances will dissolve in water.

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(5) Properties of Water

  • High Specific Heat:�
    • Specific Heat 🡪 Amount of heat energy a substance must absorb to increase 1 gram of a substance by 1 degree Celsius.�
    • Water resists changes in temperature.�
    • Makes water a more stable environment.

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  • High Heat of Vaporization:�
    • Heat of Vaporization 🡪 Amount of heat energy a substance must absorb before evaporating.�
    • Water transfers a large amount of heat when changing states. ��
  • Universal Solvent.���
  • Less Dense as a Solid than Liquid �(Assists with nutrient cycling in aquatic environments).

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  • Strong Cohesion Tension:�
    • Cohesion 🡪 Water molecules are attracted to each other, and pull on each other. �
    • Capillary Action 🡪 Water naturally spreads/flows due to cohesion + adhesion.�
    • High Surface Tension 🡪 Strong surface interlocking of water molecules due to cohesion.�
    • Adhesion 🡪 Water molecules are attracted to unlike substances (known for forming meniscus in glassware).

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(6) pH

  • Measure of acidity and alkalinity of a solution.�
  • Acid = pH of 0-6.9 = High concentration of H+ ions in solution.�
  • Neutral = pH of 7�
  • Base = Alkaline = pH of 7.1-14 = Low concentration of H+ ions / �High Concentration of OH- ions in solution�

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  • What does pH mean?�
    • pH = # = 1 x 10-# Moles of Hydrogen Ions / Liter of Solution�
    • Each pH level going “down” is 10x more acidic than the last.�
    • Each pH level going “up” is 10x more basic / alkaline than the last.

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(7) pH in Living Systems

  • Common pH Measurements:
    • Stomach Acid = 2
    • Human Blood = 7.4
    • Acid Rain = 1.5-5.4
    • Saliva = 6.5
    • Intestine = 8.3�

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  • Bicarbonate & Buffers:�
    • Buffer 🡪 A substance that resists changes to pH by absorbing excessive H+ ions, or releasing H+ ions.�
    • Bicarbonate is a buffer in our cells and aquatic systems. �
      • pH too HIGH (Alkaline) = Carbonic Acid releases H+ 🡪 Become Bicarbonate�
      • pH too LOW (Acidic) = Bicarbonate absorbs H+ 🡪 Becomes Carbonic Acid

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