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Trigonal planar electron-group arrangement with one lone pair. →Two atoms attached to the central atom + one lone pair (AX2E) → Bent shape.
Typology: Lecture notes
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Two
atoms attached to the central atom +
one
lone
pair (
Bent shape
The
lone pair is bulkier
and repels the bonding
pairs stronger
bond angle is less than 120
2
Three
atoms attached to the central atom +
one
lone
pair (
Trigonal pyramidal shape
The
lone pair is bulkier
and repels the bonding
pairs stronger
bond angles are less than 109.
3
Two
atoms attached to the central atom +
two
lone
pairs (
2
Bent shape
The
two lone pairs
have even greater repelling
effect
bond angles are less than 109.
2
3
lone pair-lone pair > lone pair-bonding pair >bonding pair-bonding pair^ ⇒
In the electron arrangement, lone pairs occupypositions as far from one another and frombonding pairs as possible
2
and
3
lone pairs occupy
equatorial
positions
(provides more space for the lone pairs andminimizes the repulsion)
, and
2
lone pairs occupy positions opposite to
each other
(provides the lowest repulsion)
Bent
Trigonal pyramidal
See-saw
Square pyramidal
~
o
~
o
~
o (^) ~
o
~
o
~
o
Bent
~
o
T-shaped
~
o
Linear
Square planar# e-groups = 6# lone pairs = 2
90
o
Summary of molecular shapes for central atomswith lone pairs
bond angles and VSEPR class
appropriate positions around the central atom andpredict any deviations from the ideal bond angles
not cancel each other
is a polar
molecule because thebond dipoles of theO-H bonds do notcancel due to the bentmolecular shape
6
4
2
B.p. 180
oC
Very soluble
in EtOH
Cl
Cl
Cl
Cl
B.p. 174
o^ C
Slightly soluble
in EtOH
δ−
δ−
δ−
δ−
Polar
Non-polar
n
molecules (n=2, 3, 4, 5, 6) where
are
atoms of the same element
pairs (
2
3
3
2
2
(bent), ... 2
2
3
The Lewis structure is similar to
PCl
5
(five atoms
bonded to the
atom, no lone pairs)
trigonal bipyramidal shape
The
Cl
atoms are larger and take two of the
equatorial positions; the
atoms are smaller and
take the two axial and one of the equatorial positions
The
dipoles are larger than the
P–Cl
dipoles (
is larger for
and
The molecule is
polar
dipoles don’t cancel (asymmetricarrangement)
Linear (non-polar)
Trigonal planar
(non-polar)
Tetrahedral(non-polar)
Trigonal bipyramidal
(non-polar)
Octahedral(non-polar)
180
o
120
o
o
90
o^120
o^
90
o
90
o
Summary of molecular polarities for moleculeshaving central atoms without lone pairs
Bent(polar)
Trigonal pyramidal
(polar)
See-saw(polar)
Square pyramidal
(polar)
~
o
~
o
~
o (^) ~
o
~
o
~
o
Bent(polar)
~
o
~90 T-shaped(polar)
o
Linear (non-polar)
Square planar (non-polar)
90
o
Summary of molecular polarities for moleculeshaving central atoms with lone pairs