Chemistry of Life

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Chemistry of Life
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Whats the Matter?

• Atom The most basic unit of matter
• Not all atoms are the same
• Elements a pure substance that consists of one
  type of atom.
• Represented by a one or two letter symbol
• 90 naturally occurring, 22 synthetic
• Of the 90 naturally occuring, only 25 are needed
  by life.
• CHON makes up 96 of these 25.
• The different elements are determined by amount
  and arrangement of sub- atomic particles.

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Subatomic Particles

• Nucleus Center of Atom ( Charge)
• Protons ( charge)
• Neutrons (0 charge)
• Cloud around the nucleus
• Electrons (- charge)

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The Electron Cloud

• Electrons are moving around the nucleus at
  distinct energy levels (shells, or orbitals)
• Each energy level has a limited capacity of
  electrons.
• 1st (closest to nucleus) 2 electron max
• 2nd and higher 8 electron max
• In their most isolated state, atoms have equal
  numbers of electrons and protons so that they
  have no overall charge

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Atomic Properties

• Atomic Number The number of protons in the
  nucleus.
• Determines which element is which
• Also indicates how many electrons will be found
  in the cloud for that element.
• Mass Number (Atomic Mass) The overall mass of
  the atom of that element
• Sum of the number of protons and the number of
  neutrons.

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• Knowing the atomic number and the mass number,
  how could you determine the number of neutrons in
  the nucleus of an atom?
• Mass - Atomic number of neutrons
• Isotopes

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The Octet Rule

• Atoms interact with each other in order to fill
  their outer most energy level with electrons.
  (usually eight)
• Most atoms do not have full outer shells
• Does CHON?
• This causes atoms to react with other atoms (by
  forming bonds) to form compounds.

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Chemical Bonds

• The emergent properties of a compound.  The metal
  sodium combines with the poisonous gas chlorine
  to form the edible compound sodium chloride, or
  table salt.

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Compounds

• A substance formed by the chemical combination of
  two or more elements in definite proportions.
• Formed due to the needs of atoms to have outer
  shells that are full with electrons.
• Nearly all matter on this planet exists in the
  form of compounds
• What are the exceptions? ( hint look at the
  periodic table)

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Types of bonds

• 1)Ionic Bonds A bond that forms when electrons
  are transferred from one atom to another.
• When atoms gain or lose electrons they become
  charged atoms called ions.
• The opposing charges of ions cause the bond to
  form.
• How does sodium (Na) and chlorine (Cl) interact?
  (hint draw bhor models)

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Mostly abiotic factors form and break
Ionic bonds Ca Cl (hint think of quantity of
atoms needed)
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Types of Bonds

• 2) Covalent Bonds A bond that forms between
  atoms when electrons are shared.
• The electrons actually travel in the orbitals of
  both atoms aka shared.
• Ex. H O, C H, N H, O O
• Can have single covalent bonds (2 e-), double
  covalent bonds (4 e-) or Triple(6e-)
• Molecules Compounds that are held together by
  covalent bonds.
• Typically biotic factors form and break covalent
  bonds.

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Water as a Molecule
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Water is a polar molecule

• Polarity When the sharing of electrons in a
  molecule is uneven.
• This results in the molecule having a slight
  negatively charged side and a slight positively
  charged side

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Hydrogen Bonds

• Because of their differing charges on either
  side, polar molecules (like water) can form
  hydrogen bonds.
• Week bond between the hydrogen of one polar
  molecule and the oxygen from another polar
  molecule
• Venn Diagram

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Hydrogen bonds between water molecules.  The
charged regions of a polar water molecule are
attracted to oppositely charged parts of
neighboring molecules. Each molecule can
hydrogenbond to multiple partners, and these
associations are constantly changing. At any
instant in liquid water at 37ºC (human body
temperature), about 15 of the molecules are
bonded to four partners in shortlived clusters.
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Ice crystalline structure and floating barrier. 
In ice, each molecule is hydrogenbonded to four
neighbors in a threedimensional crystal. Because
the crystal is spacious, ice has fewer molecules
than an equal volume of liquid water. In other
words, ice is less dense than liquid water.
Floating ice becomes a barrier that protects the
liquid water below from the colder air. The
marine organism shown here is called a euphausid
shrimp it was photographed beneath the Antarctic
ice.
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Cohesion and Adhesion

• Cohesion The attraction between molecules of the
  same substance
• Due to hydrogen bonding
• Results in the high surface tension of water
• Adhesion The attraction between molecules of
  different substances.
• Meniscus in a graduated cylinder.

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Walking on water.  The high surface tension of
water, resulting from the collective strength of
its hydrogen bonds, allows the water strider to
walk on the surface of a pond. Due to what
property of water?
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• Why is it unlikely that two neighboring water
  molecules would be arranged like this?

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Copy this chart down on a separate sheet of paper
Demonstration Observation of water drop(s) Conclusion
Wax paper
Notebook paper
Coin
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Acids, Bases, and pH

• Acids any compound that forms H ions in a
  solution.
• Bases any compound that forms OH- ions in a
  solution.
• The pH scale A measurement system that uses the
  concentrations of H ions and OH- ions in a
  solution

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