Chemical Bonding

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Chemical Bonding

• Chapter 12

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May the force be with you

• Chemical Bond The force that holds 2 or more
  atoms together and makes them function as a unit.
  (Intramolecular force)
• Bond Energy The energy required break a given
  chemical bond

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Types of Chemical Bonds

• Ionic Bonding Electrons are transferred from one
  atom to another. (Ions are formed)
• Metal Non Metal

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• Covalent Bonding Electrons are shared between
  atoms (NO ions)
• nonmetal nonmetal

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Some at ms dont like to share.

• Electronegativity Tendency of an atom to attract
  electrons in a chemical bond.

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If one atom in a bond has a greater
electronegativity

• Polar Covalent Bond Unequal sharing of
  electrons.
• The electrons still are not completely
  transferred!

Covalent
Polar Covalent
Ionic
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Determining Bond Polarity

• Look up the electronegativities of both atoms
  involved in the bond.
• If theres a difference, its a polar bond.
• The bigger the difference, the more polar.
• Polar bonds?
• O-H, S-H, P-S, F-S, N-O, H-H

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Representing Polar Bonds
A dipole is drawn with a plus sign on the
lower electronegative element with an arrow
going towards the more electronegative element.
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More dipoles
More on what polarity means to molecules to come
in later units.
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A closer look at ionic bonding

• A few observations

Plus, the noble gases dont react. What does it
all mean?
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Lets look at the e- configurations
See a pattern?!??!?
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The envy of the all the elements the noble gases

• When atoms become ions they want to have a noble
  gas electron configuration
• Metals lose electrons to reach noble gas
  configuration
• Nonmetals gain electrons to reach noble gas
  configuration
• But what do ionic compounds look like?

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LiF
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(No Transcript)
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What about nonmetals?

• A few things to remember
• ONLY THE VALENCE ELECTRONS ARE INVOVLVED IN
  CHEMICAL BONDING!!
• ATOMS WANT TO ACHIEVE A NOBLE GAS e-
  CONFIGURATION
• A Lewis Structure is a representation of a
  molecule that shows how the valence electrons are
  arranged among the atoms in the molecule

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Back to noble gases

• Neon 1s22s22p6 8 valence electrons
• Argon 1s22s22p63s23p6 8 valence e-
• Xenon 1s22s22p63s23p64s23d104p6 8 valence e-
• See a pattern?
• Octet Rule Atoms (except for hydrogen helium)
  want to be surrounded by 8 electrons in the
  valence principle energy level.
• Hydrogen and helium want to be surrounded by 2
  valence electrons, known as the duet rule

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Steps for writing Lewis Structures

• Obtain the sum of the valence electrons from all
  of the atoms. Do not worry about where the
  electrons come from, just find the sum.
• Use one pair of electrons (or a line) to form a
  bond between each pair of bound atoms.
• Arrange the remaining electrons to satisfy the
  octet (or duet) rule.
• Check to make sure you have the right number of
  electrons and that each atom as the octet rule
  satisfied.

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Your first Lewis StructureF2
Lone Pairs of e- -Nonbonding pairs -Not
involved with the bonding
Electrons
F
F
More lone pairs
Bonding Electron Pair Shared Between Both Atoms
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Often, a line will represent a bonding pair of
electrons

F
F
F F
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Lewis Structure for Water
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Atoms that really like to share

• Single bond covalent bond in which 1 pair of
  electrons is shared by 2 atoms
• Double bond covalent bond in which 2 pairs of
  electrons are shared by 2 atoms
• Triple bond covalent bond in which 3 pairs of
  electrons are shared by 2 atoms

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Resonance

• A molecule shows resonance when more than one
  Lewis structure can be drawn for the molecule

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What about polyatomic ions?

• Same rules apply as with molecules, only add or
  subtract the charge of the ion from the total
  valence electrons.
• Draw the Lewis Structure for CN-
• Hint There are 10 total valence electrons.

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C N -
NOTE The Lewis Structure is put in brackets
with the charge outside of it to indicate that
the structure is an ion.
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There are a few exceptions

• BF3
• NO
• NO2

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Were going 3D!

• What do these molecules look like?
• What is their shape?
• VSEPR Theory
• VSEPR Valence Shell Electron Pair Repulsion
• Electrons have the same charge, so they repel
  each other.
• VSEPR works on putting electron pairs (both
  bonding and lone pairs) as far apart from each
  other.

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Steps for VSEPR Theory

• Draw the Lewis Structure
• Count the electron pairs and arrange them so that
  they are as far apart from each other as possible
• Determine the positions of the atoms from where
  the bonding electron pairs are shared.
• Name the molecular structure based on the
  positions of the atoms

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Oh the possibilities
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Remember

• A double or triple bond acts as a single electron
  pair in VSEPR

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Polar Bond Polar Molecule?

• What is a polar bond?
• Nonpolar bonds never produce polar molecules
• Polar bonds usually produce polar molecules,
  unless the polar bonds cancel each other out.