VSEPR: covalent structure
The COVALENT BOND
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Electrons are NOT transferred.
Electrons are shared between the nuclei of the two atoms in a bond
A single covalent bond is a PAIR of shared electrons between two
nuclei.
A double covalent bond is 2 PAIR of shared valence electrons.
Non-polar covalent bonds have an ionic character of 0.0.
Ionic character of above 0.0 to about 0.4 are so weakly polar that
their polarity is negligible.
Compounds with an ionic character of 0.4 to 1.7 are polar, UNEQUAL
sharing of the electron pairs.
Covalent boding is the only type of bonding that creates molecules,
these molecules have definite geometry.
VSEPR: valence shell electron pair repulsion theory
OBJECTIVES: -To Construct Lewis Dot Structures for Covalent
Compounds AND ACCOUNT FOR EACH VALENCE
ELECTRON IN THE STRUCTURE..
-To calculate molecular geometry
-To assess symmetry of the molecules.
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THE VSEPR METHOD AND PROCESS.
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STEP ONE: CALCULATE THE VALENCE ELECTRONS
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STEP TWO; DRAW WITH SINGLE BONDS ONLY
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PLACE THE LEAST ELECTRONEGATIVE ATOM IN THE CENTER.
H CANNOT BE IN THE CENTER EVEN IF LEAST ELECTRONEGATIVE.
SINGLE BOND IT TO THE SURROUNDING ATOMS (LIGANDS)
STEP THREE:
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MULTIPLY EACH BOND BY 2 TO GET THE ELECTRONS THAT ARE INVOLVED IN
BONDING.
SUBTRACT THE BONDING ELECTRONS FROM THE VALENCE ELECTRONS.
STEP FOUR-A:
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ADD THE GROUND STATE VALENCE ELECTRONS OF EACH ATOM IN THE
SUBSTANCE.
DRAW ELECTRONS AS DOTS TO COMPLETE THE OCTET OF EACH ATOM
(EXCEPT H), SUBTRACT THOSE ELECTRONS FROM THE TOTAL THAT REMAIN
IN STEP THREE.
STEP FOUR-B: PLACE ANY REMAINIG ELECTRONS ON THE CENTRAL ATOM
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Example one, ammonia, NH3
STEP ONE – ADD VALENCE ELECTRONS
( first use ionic character to verify covalent bonding).
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N has 5 valence electrons ( 2-5)
: 5
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Each of the 3 H atoms has one electron : 3
8 electrons total
STEP TWO – DRAW, here N must be central as H cannot
2 bonding e-
H
H
N
H
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Example one, ammonia, NH3
STEP ONE – ADD VALENCE ELECTRONS.
–
N has 5 valence electrons ( 2-5)
: 5
–
Each of the 3 H atoms has one electron : 3
8 electrons total
STEP TWO – DRAW, here N must be central as H cannot
4 bonding e-
H
H
N
H
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•
•
Example one, ammonia, NH3
STEP ONE – ADD VALENCE ELECTRONS.
–
N has 5 valence electrons ( 2-5)
: 5
–
Each of the 3 H has one electron
: 3
8 electrons total
STEP TWO – DRAW, here N must be central as H cannot
6 bonding e-
H
H
N
H
•
•
•
Example one, ammonia, NH3
STEP ONE – ADD VALENCE ELECTRONS.
–
N has 5 valence electrons ( 2-5)
: 5
–
Each of the 3 H has one electron
: 3
8 electrons total
STEP TWO – DRAW, here N must be central as H cannot
( 8 total electrons ) – ( 6 bonding e- ) = 2 remain, place on central atom (N)
H
H
N
H
H N H
H
1. The ammonia molecule has ONE UNBONDED PAIR of electrons and
THREE COVALENT BONDS: one pair and three bonds.
2. This pattern indicates a TRIGONAL PYRAMIDAL GEOMETRY.