Bonds

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Bonds

• The eternal mystery of the world is its
  comprehensibility
• - Albert Einstein

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Chemical Bonds

• Chemical compounds are formed by the joining of
  two or more atoms.
• This point of union is called a bond.
• The bond means there is an attractive force
  between the atoms.
• Bonds are more like springs then sticks. Some
  atom movement is possible.
• There are 3 main types of bonds, Ionic, Metallic
  and Covalent.

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Ionic Bonds

• Ionic bonds are formed by a transfer of
  electrons.
• One of the atoms gains the electron(s) that the
  other lost.
• Both end up with full outer energy levels and
  opposite charges.
• The oppositely charged ions are attracted to each
  other.
• Many ions bond together forming networks.
• This is shown in the diagram of NaCl to the
  right.
• In the diagram, Na is red and Cl is green.
• In this situation there really is no single
  molecule but there is a simplest formula..

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Ionic Bonds

• Ionic bonds are formed by a transfer of
  electrons.
• One of the atoms gains the electron(s) that the
  other lost.
• Both end up with full outer energy levels and
  opposite charges.

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Ionic compounds and conduction

• Electric current is moving charges.
• Solid ionic compounds do not conduct electricity
  because the charged ions are locked in place.
• When dissolved, ionic compounds disassociate or
  separate into their ions.
• The solution can now conduct electricity because
  the ions are free to move.
• A solid block of salt and a beaker of distilled
  water will not conduct electricity, but a beaker
  of salty water will!

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Metallic Bonds

• The attraction between a metal atoms nucleus and
  a neighboring atoms electrons is strong and packs
  the atoms closely together.
• This causes the outermost energy levels of the
  atoms to overlap.
• These outermost electrons are free to move from
  atom to atom.
• This explains why metals are good conductors and
  why they are so flexible and malleable when
  compared to the non-metals.

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Covalent Bonds

• A covalent bond forms when two or more atoms
  share valence electrons.
• This occurs most often between elements in groups
  IVA, VA, VIA and VIIA.
• The sharing of electrons allows each atom in the
  molecule to have a stable octet in its outermost
  energy level.

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Methane (CH4)

• The methane molecule illustrated has 4 covalent
  bonds.
• The bonds are between each hydrogen atom and the
  carbon atom.
• The sharing of electrons means sometimes they are
  going around the carbon and sometimes they are
  going around the hydrogens.
• In this way each element gets to have a full
  outer energy orbital.

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Polar Covalent bonds

• The shared electrons in a covalent bond may not
  be shared equally.
• Electrons are strongly attracted to atoms located
  to the upper right of the periodic table.
• In the water molecule, the oxygen atom has a much
  stronger attraction for the electrons then either
  hydrogen.
• This means that the electrons from the two
  hydrogens spend most of their time orbiting the
  oxygen atom.
• Because of this unequal sharing a molecule of
  water has a negative and a positive end (poles).

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Water is Special!

• Because of the polar nature of the water molecule
  it is attracted to itself!
• Water molecules are attracted to each other and
  this is the main reason that such a small
  molecule is a liquid at room temperature!

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Many water molecules showing hydrogen bonding
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Ice Structure - note similarities to snowflakes!
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Glacial Blue ice - ice that is formed by the
recrystallization of snow that is compacted in a
glacier.
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Huge tabular iceberg from Antarctica
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Blue ice berg, Antarctica
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Carbon dioxide, polar covalent but with a twist!

• In the CO2 molecule the oxygen atoms have the
  electrons more often than the carbon atoms.
• This makes the oxygen ends of the molecule
  negative and the area between the oxygen and the
  carbon positive.
• How does this explain the fact the CO2 is a gas
  at room temperature even though it is a much
  bigger molecule than water?

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Dry Ice

• Dry ice is the solid form of the gas carbon
  dioxide. 
• A full block, measuring about 10 inches square,
  weighs 50 lbs. 
• The temperature of dry ice is 110 below zero. 
• When handling dry ice, wear work gloves as the
  extremely low temperature will cause frostbite. 
• Dry ice has many uses, chief among them as a
  refrigerant to prevent food form perishing and to
  ship blood products.

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