Chapter 2 The Chemical Basis of Life

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Chapter 2 The Chemical Basis of Life

• Please take the following notes Cornell style.

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Chapter 2.1 Living organisms are composed of
about 25 elements-

• Chemical composition of the human body
• Major elements - O, C, H, N, Ca, P, K, S, Na, Cl,
  Mg
• Trace elements - B, Cr, Co, Cu, F, I, Fe, Mn, Mo,
  Se, Si, Sn, V, Zn

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Chapter 2.2 Trace elements are common additives
to food and water-

• Why is it important to
• our health and well
• being that trace
• elements are added to
• our food and water?
• Dietary deficiencies
• in trace elements can
• cause various
• physiological
• conditions.

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Chapter 2.3 Elements can combine to form
compounds-

• Most chemical compounds in living organisms
  contain at least three or four different elements
  mainly C, H, O, and N.
• Why are sodium chloride and vitamin A both
  classified as compounds?
• ? They contain two or more elements.

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Chapter 2.4 Atoms consist of protons, neutrons
and electrons-

• The smallest particle of matter that still
  retains the properties of an element is an atom
• An atom is made up of protons and neutrons
  located in a central nucleus
• The nucleus is surrounded by electrons arranged
  in electron shells
• Atoms of the same element always have the same
  number of protons (atomic number)
• Be sure you review your Chapter 2 Vocabulary
  atomic number, mass number, atomic mass, etc.

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Chapter 2.4 Atoms consist of protons, neutrons
and electrons-

• B. All elements have the same characteristics,
  but can have different number of neutrons. These
  are called isotopes. Some isotopes are
  radioactive.

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Chapter 2.5 Radioactive isotopes can help or harm
us-

• Basic research and medical diagnosis
• Radioactive tracers help track molecules in
  living organisms and can be used to help
  track/locate disorders and diseases.
• Dangers
• Radioactive isotopes can damage cells, especially
  DNA, by breaking important chemical bonds

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Chapter 2.6 Electron arrangement determines the
chemical properties of an atom-

• Electrons in an atom are arranged in shells,
  which may contain different numbers of electrons.

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Chapter 2.6 Electron arrangement determines the
chemical properties of an atom-

• Atoms whose shells are not full tend to interact
  with other atoms and gain, lose, or share
  electrons
• These interactions form chemical bonds

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Chapter 2.7 and 2.8 Ionic and Covalent bonds-

• Ionic bonds are attractions between ions of
  opposite charge
• When atoms gain or lose electrons, charged atoms
  called ions are created

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Chapter 2.7 and 2.8 Ionic and Covalent bonds-

• In covalent bonds two atoms share one or more
  pairs of outer shell electrons, forming molecules

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Checkpoint

• Fill-in your summary.
• Look over notes and place a star next to anything
  that is unclear or anything that you want to look
  up in your textbook.
• Ask Mrs. Green if you need clarification on any
  topic covered today.
• Daydream about how awesome your biology teacher
  is.

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Chapter 2.9 Unequal electron sharing creates
polar molecules

• The more electronegative (attraction for
  electrons) an atom is, the stronger its pull on
  the electrons are in a covalent bond.
• Non polar molecules have electrons that are
  shared equally between atoms.
• Polar covalent bonds have electrons that are
  shared unequally.
• Which would have a higher electronegativity an
  oxygen atom or a hydrogen atom?

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• Example In water (H2O), the oxygen is more
  electronegative, so the electrons are pulled more
  toward it, thus creating a slight negative charge
  at the oxygen end and a slight positive charge on
  the hydrogen end of the molecule.

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Chapter 2.10 Hydrogen bonds are weak bonds
important in the chemistry of life.

• Hydrogen bonds are the weak interaction between
  the slightly positive hydrogen end and slightly
  negative oxygen end of a molecule.
• What allows neighboring water molecules to
  hydrogen bond to one another?

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Waters Life Supporting Properties

• Chapter 2.11 Hydrogen bonds make liquid water
  more cohesive
• Cohesion (waters ability to stick to itself and
  other things) is due to hydrogen bonding.
• Water has a high surface tension because hydrogen
  bonding keeps the surface of water together.

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Surface tension
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Capillary action
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adhesion
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Waters Life Supporting Properties

• Chapter 2.12 Waters hydrogen bonds moderate
  temperature
• Hydrogen bonding allows water to better resist
  temperature change by allowing water to store
  great amounts of energy and slowly release it.

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Waters Life Supporting Properties

• Chapter 2.13 Ice is less dense than liquid water
• As water freezes, hydrogen bonds become more
  stable creating a crystal structure that has more
  open space than liquid water.
• This makes ice less dense than liquid water,
  where the hydrogen bonds are more tightly packed
  together.
• If ice sank, then eventually all ponds, lakes and
  even oceans would freeze solid.

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Waters Life Supporting Properties

• Chapter 2.14 Water is the solvent of life
• Water is able to dissolve many ionic, polar
  molecules and compounds because of its own slight
  polarity.

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Water true/false Are you a water expert??

• Condensation is water coming out of the air.
• Rainwater is the purest form of water.
• If you filled a glass full of water from the
  Great Salt Lake, when it evaporated there would
  be 1 inch of salt left.
• Raindrops are tear-shaped.
• Water boils quicker in Denver, Co. than at the
  beach.

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1. Condensation is water coming out of the air.

• TRUE
• Water that forms on the outside of a cold glass
  is liquid water condensing from water vapor in
  the air. In cold air, water vapor condenses
  faster than it evaporates. So, when the warm air
  touches the outside of your cold glass, the air
  next to the glass gets chilled, and some of the
  water in that air turns from water vapor to tiny
  liquid water droplets.

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2. Rainwater is the purest form of water.

• False
• Actually, distilled water is "purer."
• Rainwater contains tiny particles of dust and
  dissolved gasses, such as carbon dioxide and
  sulfur dioxide (yep, acid rain).

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3. If you filled a glass full of water from the
Great Salt Lake, when it evaporated there would
be 1 inch of salt left.

• True
• They don't call it the Great SALT Lake for
  nothing. About one-fifth (20) of the weight of
  the water comes from salt.
• Seawater only has a salt concentration of about 3
  1/2 . 

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4. Raindrops are tear-shaped.

• False. A falling raindrop looks more like a small
  hamburger bun!
• As rain falls, the air below the drop pushes up
  from the bottom, causing the drop to flatten out
  somewhat. The strong surface tension of water
  holds the drop together, resulting in a bun shape
  (minus the sesame seeds).

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5. Water boils quicker in Denver, Co. than at the
beach.

• TRUE! The boiling point of water gets lower as
  you go up in altitude. At beach level, water
  boils at 100C. But at 5,000 feet, about where
  Denver is located, water boils at 94 C.
• This is because as the altitude gets higher, the
  air pressure (the weight of all that air above
  you) becomes less. Since there is less pressure
  pushing on a pot of water at a higher altitude,
  it is easier for the water molecules to break
  their bonds and boil.