Emeltingpointboilingpointandsolubilityofacompound

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Unformatted text preview: on
density
or
are
 negative.

These
region
would
tend
to
attract
positively
charged
species.

Parts
of
the
 molecule
which
are
blue
have
relatively
less
electron
density
or
are
positive.

These
region
 would
tend
to
attract
negatively
charged
species.
 The
MEP
is
plotted
at
the
van
Der
Waals
surface
of
a
molecule.

This
is
the
farthest
extent
 of
a
molecule’s
electron
cloud
and
therefore
indicates
the
shape
of
the
molecule.
 The
MEP
of
hydrogen
chloride
clearly
indicates
that
the
negative
charge
is
concentrated
 near
chlorine.

The
overall
shape
of
the
molecule

is
also
represented
as
follows:
 The
Dipole
Moments
of
Representative
Molecules
 In
diatomic
molecules
a
dipole
exists
if
the
two
atoms
are
of
different
electronegativity.
 In
more
complicated
molecules
the
molecular
dipole
moment
is
the
sum
of
the
bond
 dipoles.

A
bond
dipole
or
bond
moment
is
a
vector;
it
has
both
direction
and
magnitude.
 Some
molecules
with
very
polar
bonds
will
have
no
net
molecular
dipole
because
the
 bond
dipoles
cancel
out.

The
center
of
positive
charge
and
negative
charge
coincide
in
 these
molecules
 Examples:
 In
carbon
tetrachloride
the
bond
dipoles
cancel
and
the
overall
molecular
dipole
moment
 is
0
Debye.
 In
chloromethane
the
C‐H
bonds
have
only
small
bond
dipoles
but
the
C‐Cl
bond
has
a
 large
dipole;
the
result
is
that
the
molecule
is
quite
polar.
 An
unshared
pair
of
electrons
on
atoms
such
as
oxygen
and
nitrogen
contribute
a
great
 deal
to
the
dipole
moment
of
a
molecule.

Water
and
ammonia
are
examples.
 Water
and
ammonia
have
very
large
net
dipoles
 Some
cis‐trans
isomers
differ
markedly
in
their
dipole
moment.

In
trans
1,2‐ dichloroethene
the
two
carbon‐chlorine
dipoles
are
pointing
in
opposite
directions
and
 cancel
each
other
out;
the
molecular
dipole
is
0
Debye.

In
the
cis
isomer
the
carbon‐ chlorine
dipoles
reinforce
each
other
resulting
in
a
large
molecular
dipole
moment.
 In
Class
Problems:
 Write
the
symbol
δ+
and
δ‐
by
the
appropriate
atoms
and,
where
appropriate,
 draw
a
resultant
dipole
moment
vector
for
each
of
the
following
molecules.
 (1)  Tetrafluoromethane:
CF4
 (2)  Trifluoromethane:
CHF3
 Functional
Groups
 Functional
groups
are
characterized
by
the
presence
of
a
certain
arrangement
of
 similar
or
di...
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This note was uploaded on 06/19/2009 for the course CHEM 2311 taught by Professor Tyson during the Fall '07 term at Georgia Institute of Technology.

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