VSEPR THEORY
VSEPR Theory: (Valence Shell Electron
Pair Repulsion)
valence electrons in an atom will orient themselves to be as far apart as
possible
* CLASSES OF MOLECULES
A = central atom
B = surrounding atoms
E = unshared electron pairs on central atom
*** subscript tells how many of each you have ***
EXAMPLE: CH4
H
..
H : C : H
..
H
1 central atom,
4 surrounding atoms, no unshared e- prs. on central
atom
CLASS = AB4
EXAMPLE 2:
NH3 ..
H : N : H
..
H
1 central atom, 3 surrounding
atoms, 1 unshared e- pr. on central atom
CLASS = AB3E
* SHAPES OF MOLECULES
CLASS
SHAPE
AB2
linear
AB2E
bent
AB2E2
bent
AB3
trigonal planar
AB3E
trigonal pyramid
AB4
tetrahedral
* POLARITY OF MOLECULES (symmetry of molecules) – different from bond polarity
A MOLECULE is nonpolar if...
- there are no unshared e- pairs around the central atom
AND
- the surrounding atoms are all the same element
A BOND
is nonpolar (covalent) if…
- it occurs between two atoms of the
same element
IT
IS POSSIBLE, EVEN LIKELY, THAT A NONPOLAR MOLECULE HAS POLAR COVALENT BONDS!