Chemical Bonding Worksheets Page 15
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22MOLECULES WHERE CENTRAL ATOM HAS NO LONE PAIRS
– Consider a molecule composed of only two types of atoms, A and B
A=central atom
X=outer atoms
Table of Molecular Shapes and Bond Angles Part I
# of Outer
Bond
General formula
MOLECULAR GEOMETRY
NAME of SHAPE
Atoms
Angles
180°
AX
2
linear
180˚
2
AX
3
trigonal planar
120˚
3
120°
109.5°
AX
4
tetrahedral
109.5˚
4
When there are lone pairs of electrons around the central atom, knowing the steric number
for the central atoms can help determine the three-dimensional shape.
The steric number (number of electrons groups) on the central atom is determined as follows:
⎛
⎞
⎛
⎞
#
of
atoms
bonded
#
of
lone
pairs
+
Steric Number =
⎜
⎟
⎜
⎟
⎝
⎠
⎝
⎠
to
the
central
atom
on
the
central
atom
MOLECULES WHERE CENTRAL ATOM HAS ONE OR MORE LONE PAIRS
Lone pairs of electrons take up more space than bonded pairs of electrons because the
bonded pair are held by two atoms whereas the lone pair is held only by one atom.
A=central atom
X=outer atoms
E=lone pairs
CHEM 121 Tro Chapter 10 F2012
page 15 of 22
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