Biology 107 Chemical Context of Life

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Biology 107Chemical Context of Life

• August 30, 2002

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Chemical Context of Life

• Student Objectives As a result of this lecture
  and the assigned reading, you should understand
  the following
• 1. The six (6) major elements in living systems
  are carbon, hydrogen, nitrogen, oxygen,
  phosphorus, and sulfur (CHNOPS).
• 2. The number of protons in a nucleus determines
  the atomic number, and it is different for each
  element. The total number of protons and
  neutrons is the atomic mass number.
• 3. It is mainly the electrons and the different
  energy levels of electrons in electron shells
  that determine how an atom behaves when it
  encounters other atoms. The number of electrons
  in the outermost shell determine the chemical
  properties of an atom.

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Chemical Context of Life

• 4. When electrons move from higher electron
  shells to lower shells they give off energy.
  Conversely, energy must be supplied to move
  electrons from lower to higher shells (e.g.,
  photosynthesis, where light energy raises
  electrons to higher shells).
• 5. Atoms with filled outer shells tend to be
  relatively inactive (inert), while atoms whose
  outer shell is not full tend to interact with
  other atoms by participating in chemical
  reactions that result in the filling or emptying
  of a shell. Atoms may share or transfer electrons
  of the outer shell. These interactions typically
  result in atoms staying close together, held
  together by attractions called chemical bonds.
• 6. Chemical bonds may be ionic or covalent (polar
  or non-polar).
• 7. Atoms and molecules may also interact through
  intermolecular forces that are not chemical bonds
  (e.g., hydrogen bonds).

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The number of electrons in the outermost shell
determine the chemical properties of an atom
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The number of electrons in the outermost shell
determine the chemical properties of an atom
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When electrons move from higher electron shells
to lower shells they give off energy
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When electrons move from higher electron shells
to lower shells they give off energy
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Atoms participate in chemical reactions by
sharing or transferring electrons of the outer
shell to result in the filling or emptying of a
shell
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Atoms participate in chemical reactions by
sharing or transferring electrons of the outer
shell to result in the filling or emptying of a
shell
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Ionic chemical bonds result from the transfer of
electrons - Video
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Covalent chemical bonds result from the sharing
of electrons
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Covalent chemical bonds result from the sharing
of electrons
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Covalent chemical bonds result from the sharing
of electrons - Video
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Covalent chemical bonds which share electrons
equally are non-polar
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Covalent chemical bonds which share electrons
unequally are polar
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Covalent bonding - Video