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!

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