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Transcript 
Predicting Shapes of
Molecules
VSEPR
Valence Shell Electron Pair
Repulsion Theory
Why not the shape of
ionics?
Linear (straight line)
• Any 2 atom molecule is linear
• O2
• H2
• HCl . . . etc.
Steps to predicting shapes
1. Draw the dot structure
2. Count the electron domains
surrounding the central atom
• Single bonds count as one
• Double and triple bonds count as one
• lone electron pairs (unbonded) count
as one
3. Determine the category based on
regions of electron domains
•
•
•
•
•
2 domains - Linear
3 domains – trigonal planar
4 domains - tetrahedral
5 domains – trigonal bipyramidal
6 domains - octahedral
http://safeshare.tv/w/BUalxrqbEK
FINALLY
Name the shape of the molecule
based on the arrangement of the ATOMS
• Lone pairs are repulsive and
force the bonded electrons
together and reduce the bond
angles AND change the shape
Practice… Shape & bond angles?
• H2Se
– Bent w/ ~1050 angles
• CH2Cl2
– Tetrahedral w/ 109.5o angles
• PCl3
– Trigonal pyramidal w/ 107o angles
Types of Covalent
MOLECULES
POLAR vs. NON-POLAR
non-polar
• Have Symmetrical Shapes &
symmetrical electron distributions
Polar molecules
(a.k.a. Dipoles)
• Occurs because of a polar bond
between 2 atoms
δ+
C
O
δ
• Or uneven charge distribution
in the molecule
δ+
H Cl
δ
• or asymmetrical distribution of
electrons
Trigonal pyramidal & Bent
polarity
Water is asymmetrical
δ-
O
H
H
δ+
Water is a bent molecule
H
H
O
H
H
W-A-T-E-R
as bent as it can be!
Water’s polar MOLECULE!
Water’s polar MOLECULE!
The H is positive
The O is not - not - not - not
W-A-T-E-R
as bent as it can be!
Water’s polar MOLECULE!
Water’s polar MOLECULE!
The H‘s are the ears
The O’s the nose - nose - nose - nose
W-A-T-E-R
as bent as it can
be!
Making sense of the polar
non-polar thing
COVALENT
BONDS
or MOLECULES
non-polar are between
identical atoms or
very small e-neg
difference up to
~0.4
All other bonds with
e-neg difference up
to ~2.0 are polar
Polar
– asymmetrical
UNEVEN electron
distribution
Non-polar
– Even distribution of
electrons
– symmetrical shape
The End
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