Friday - June 18, 1999 - Molecular Geometries
2 types of bonding
Ionic- bonding between + or - ions,
electron transfer
example:
Oxygen forms a stable octet
due to the TRANSFER.
Covalent - Bonding between similarly
charged elements, usually -, electrons are shared.
example:
Both Chlorines have stable
octets.
All negative ions must have stable octets.
Double Bonds(Covalent - neagtive ions only)
example:
1 -
represents 2 e-
Since we have 4e- shared we used 2 dashed lines(=)
Lone Pair- pair of electrons which are not involved in bonding
In the example above, each oxygen has 2 lone pairs.
Triple Bonds(Covalent)
example:
In every case, the negative ion has a stable octet.
Coordinate Covalent Bond - When 1 element bonates BOTH
electrons in a covalent bond.
Carbon can't donate his lone pair because it would still be deficient.
Resonance- When a pair of electrons shift from one bond to another
quickly to make the compound seem stable.
O3 -Ozone
At "A" we
see 3 Oxygens that all need 2e-
At "B" Oxygen #1 donates 2e- to Oxygen #2 and Oxygen #2 donates
2e- to Oxygen #3.
Oxygen #2 and #3 are stable , but Oxygen #1 only has 6e-. A lone
pair from Oxygen #2 moves down to stabalize Oxygen #1.
At "C" we see that this lone pair movement creates a Double Bond.
At "D" we see that the double bond could be on either side of Oxygen
#2, so we have to show both structures.
Sigma(s) Bonds-
Single Bonds
Pi(p) Bonds
- Double Bonds
In this example we have
2 pi bonds and 9 sigma
VSEPR- Valence Shell
Electron Pair Repulsion
-as electron pairs repel, molecules adjust their
shape so that the pairs are as far apart from each other as possible.
CH4 - Methane
The 2 solid lines in the 3-d Molecular Geometry mean the hydrogens
are "IN THE PLANE"
The dashed line means the hydrogen is "OUT OF THE PLANE-above"
The black triangle means"OUT OF THE PLANE-below"
Hybridization- When atomic orbitals mix to form hybrid orbitals.
Male Donkey + Female Horse = mule(hybrid)
example: NaCl
Na - has e-'s that are in the s-block
Cl - has e-'s that are in the p-block
Since the are in different sub blocks they form a hybrid link.
Use S(holds 2e-), P(holds 6e), D(holds 10 e-)
1 bond(2e-) - S
2 bonds(4e-) - SP
3 bonds(6e-)- SP2
4 bonds(8e-)- SP3
5 bonds(10e-)-SP3D
6 bonds(12e-)- SP3D2
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Name(formula)
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Electron Dot
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Structural Formula
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3-D Geometry
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Shape
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Bond Angle
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Hybrid
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NaCl
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MgCl2
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BF3
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CH4
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PCl5
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SI6
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Exceptions(Special Cases) - Compounds in which the central atom has
lone pairs
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Name(formula)
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Electron Dot
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Structural Formula
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3-D Geometry
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Shape
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Bond Angle
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Hybrid
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H2O
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NH3
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Polar/Nonpolar Molecules- used to determine if substances will
mix or not in solution
Polar
-Has a dipole- a collection of
charge going from + to -
Assign the negative based on the most electronegative element
Example: HCl
-electronegativity differences
- not symmetrical(lone pairs)
Nonpolar
-Does not have a dipole
-electronegativity differences
-symmetrical
Note: 2 out of the three must fit
example: CH4
Isomers-same formula, different structure
example: C4H8