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Atoms, Molecules, and Life

Atoms, Molecules, and Life

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Ap Bio Ch2 PowerPoint Ap Bio Ch2 PowerPoint Presentation Transcript

  • Atoms, Molecules, and Life
    • Covalent bond — electrons shared
      • Shared unequally — polar
      • Shared equally — nonpolar
    • Ionic bond — electron transfers total #
      • Both atoms ionized
      • May dissociate in water
    Chemical Bonding
  • Bonding Involves Electrons
    • One pair electrons per bond
    • Outer electrons form bonds
    • Behave using “ octet rule ”
    • If nearly eight in outer shell
      • Desires more electrons
      • Oxidizer
    • If less than four in outer shell
      • Desires fewer electrons
      • Reducer
  • Most Elements Molecular (a) In hydrogen gas, one electron from each hydrogen atom is shared, forming a single covalent bond. The resulting molecule of hydrogen gas is represented as H–H or H 2 . (b) In oxygen gas, two oxygen atoms share four electrons, forming a double bond (O=O or O 2 ).
  • Ionic Bonding in NaCl Sodium ion #e=#p-1 Chlorine ion #e=#p+1 Negative charge Positive charge ± + – ± + ± + ± + ± + ± + ± + ± + – – – – – – ± + – – – ± + – ± + ± + ± + ± + ± + ± + ± + – – – – – – ± + – – – – – – – – – – ± + – ± + ± + ± + ± + ± + ± + ± + – – – – – – ± + – – – – Sodium #e=2+8+1=#p ± + – ± + ± + ± + ± + ± + ± + ± + – – – – – – ± + – – – – – – – – – – Chlorine #e=2+8+7=#p – – – Electron Completely Transferred
  • Ionic Bonding in NaCl
    • Opposites attract.
    • Sodiums nestle between chlorines.
    • Perfectly cubical crystals.
    Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Cl - Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na + Na +
  • Water Is Covalent
    • Electron pair forms covalent bond
    Each spends some time w/one, then the other atom Less time w/H, more time w/O Causes polarity of H 2 O molecule
  • Water Molecule H 2 O Oxygen Hydrogens H H O
  • Polar vs. Nonpolar Bonds
    • Distribution of charge on molecule
    • Polar — charged surface
      • Prefer other charged molecules
      • Soluble in water
    • Nonpolar — no residual charge
      • Prefer uncharged molecules
      • Soluble in oils
  • Bonding Patterns of Common Atoms       Sulfur Phosphorus Oxygen Nitrogen Carbon Hydrogen
  • Free Radicals
    • Some cellular reactions produce free radicals
      • Free radical : a molecule whose atoms have one or more unpaired electrons in their outer shells
    • Free radicals are highly unstable and reactive
      • Free radicals steal electrons, destroying other molecules
      • Cell death can occur from free radical attack
  • Free Radicals
    • Free radicals are involved in causing heart disease, Alzheimer’s, cancer, and aging
    • Antioxidants like vitamins C and E render free radicals harmless
  • Hydrogen Bonds O O H H H H + + + – – + + Hydrogen Bonds Water molecules carry slight charges Electrons favor O over H Hydrogen bonds form between O of one and H of another Not a “REAL” bond!!! No transfer of electrons!
  • Hydrogen Bonds Hydrogen bonds are like two children holding very-slippery hands. The bonds constantly break and reform
  • NaCl Dissolved by Water NaCl is ionicly bonded Water is polar and charged O sticks to Na + H sticks to Cl -
  • Dissociation + Water Hydroxide ion Hydrogen ion A few water molecules naturally dissociate
    • Hydroxide ion is negative and basic
    • Hydrogen ion is positive and acidic
    Makes water a good solvent H 2 O Glucose H 2 O H 2 O H 2 O H 2 O – + Hydrogen Bond
  • Cohesion among Water Molecules
  • The pH Scale Neutral pH + = pOH – Increasingly Acidic pH + > pOH – Increasingly Basic pH + < pOH – 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 -14 Lemon Juice Lime Juice Stomach Acid Coffee Urine Water Blood Sea Water Baking Soda Bleach Ammonia Oven Cleaner
  • Water Stabilizes Temperature
    • Very low or very high temperatures may damage enzymes or slow down important chemical reactions
    • Water moderates the effect of temperature change
      • Temperature reflects the speed of molecular motion
      • It requires 1 calorie of energy to raise the temperature of 1g of water 1 o C (the specific heat of water), so it heats up very slowly
  • Water Stabilizes Temperature
    • Water requires a lot of energy to turn from liquid into a gas ( heat of vaporization )
      • Evaporating water uses up heat from its surroundings, cooling the nearby environment (as occurs during sweating)
      • Because the human body is mostly water, a sunbather can absorb a lot of heat energy without sending her/his body temperature soaring
  •  
  • Water Stabilizes Temperature
    • Water requires a lot of energy to be withdrawn in order to freeze ( heat of fusion )
    • Water freezes more slowly than other liquids
    • Most substances become denser when they solidify from a liquid
    • Ice is unusual because it is less dense than liquid water
  • Water molecules spread apart slightly during the freezing process
  •  
  • Water Forms an Unusual Solid
    • Ice floats in liquid water
    • Ponds and lakes freeze from the top down and never freeze completely to the bottom
      • Many plants and fish therefore are not frozen
  • The End