The document discusses the valence shell electron pair repulsion (VSEPR) model, which uses the number of electron pairs around an atom to predict the geometry of molecules. It can be used to predict structure by considering the number of bonded atoms and lone pairs on the central atom. The model works well but is an oversimplification in some cases, failing to accurately describe resonant or planar structures.

1. Is based on the number of
regions of high electron density
around the central atom
Electron density: The
number of electrons in a unit
volume.
Can be used to predict the
structure of a molecule
model Does fail in some cases;
models are oversimplifications

2.  Electron pair: those electrons
 Valence electrons: the electrons in that are in the same orbital.
the last shell or energy level of an Bonds are also electron pairs.
atom. These are responsible for the
interactions made with other atoms › Both the electron pairs in
the formation of chemical bonds). chemical bonds and lone pairs
are considered to determine
 Lewis structure: A structural formula the structure of a molecule.
in which electrons are represented by
dots; two dots between atoms
represent a single bond, four dots
between atoms represent a double
bond, and six dots represent a triple
bond.
› A single bond is represented by one
line, a double bond by two lines, and a
triple bond by three lines each line
represents two electrons.

3. You may recall that electrons repel each
other because of their negative charge.
Electrons in lone pairs repel electrons
involved in bonding.
These repulsions determine the bond angles.

4.  Draw the Lewis Structure
 Count how many atoms have bonded to the
central atom.
› Name the central atom “A” and the surrounding
atoms “B”
 Count how many lone pairs the central atom
has
› Name these “E”
 Consult the VSEPR chart.
› When you consult the chart, remember that the

5. Linear
Bent
Trigonal
Planar

6. Tetrahedral Trigonal Bipyramidal
T-
shaped
Trigonal
Pyramidal Seesaw

7. Octahedral
Square
Pyramidal
Square
Planar

8. Total Electron Generic Bonded Lone Molecular Exampl
Domain Geometry Formula Atoms Pairs Shape e
s
1 Linear AB 1 0 Linear H2
AB2 2 0 Linear CO2
2
Linear
ABE 1 1 Linear CN-
B= Bonded Atoms
A= Central Atom
AB3 3 0 Trigonal BF3
E= Lone pairs
Planar
3 Trigonal
Planar AB2E 2 1 Bent O3
ABE2 1 2 Linear O2
AB4 4 0 Tetrahedral CH4
AB3E 3 1 Trigonal NH3
Tetrahedra pyramid
4
l
AB2E2 2 2 Bent H2O
ABE3 1 3 Linear Cl2

9. Total Electron Generic Bonded Lone Molecular Example
Domain Geometry Formula Atoms Pairs Shape
s
AB5 5 0 Trigonal PF5
Bipyramid
AB4E 4 1 See Saw SF4
Trigonal
B= Bonded Atoms
5
Bipyramid 3 2 T shape
A= Central Atom
AB3E2 ClF3
E= Lone pairs
AB2E3 2 3 Linear I3 -
AB6 6 0 Octahedral SF6
AB5E 5 1 Square IF5
6 Octahedral pyramidal
AB4E2 4 2 Square XeF4
planar
http://intro.chem.okstate.edu/1314f00/lecture/chapter10/vsepr.html
http://www.sciencegeek.net/Chemistry/Presentations/VSEPR/
http://www.sciencegeek.net/APchemistry/Presentations/8_VSEPR/inde

10.  STEP 1: Draw the Lewis structure
› Remember how many valence
electrons the central atom has (in
this example, H)
 One molecule can only have one
central atom.
› Remember the valence electrons the
bound atoms have (the other
hydrogen) just so you know how the
chemical bonds are being formed.
 The lone pairs of these B atoms don’t
determine the molecule’s structure in
this VSEPR model.

11. ONLY in diatomic
molecules, chose one or other
atom to be the central atom, as
both have the same
characteristics. You determine
which one is A and which one is B
 STEP 2: Count how just to keep track of the electrons
many atoms have in bonds and lone pairs.
bonded to the central No lone pairs in
atom. atom A (central
atom)
› ANSWER: 1
 STEP 3: Count how
many lone pairs the
central atom has
› ANSWER: 0 One B atom

12.  STEP 4: Check the
VSEPR chart:
› Total number of
domains (1+0=1)
› Bonded atoms: 1
› Lone pairs: 0
 ANSWER: LINEAR

13.  STEP 1: Draw the Lewis
structure
› Remember how many valence
electrons the central atom has
(in this example, C)
› Remember the valence
electrons the bound atoms have
(the two oxygens) just so you
know how the chemical bonds
are being formed.
 The lone pairs of these B atoms

14. No lone
 STEP 2: Count how many pairs in atom
A (central
atoms have bonded to the atom)
central atom.
› ANSWER: 2
 STEP 3: Count how many
lone pairs the central atom
Two B atoms
has

15. Remember the repulsion
between electrons: as each
electron pair repel each
other, they’ll try to be as far
as possible from each other.
 STEP 4: Check the  They can be as far as
VSEPR chart: 180ª from each other (the
largest bond angle being
› Total number of 180ª).
domains (2+0=2) As there are no lone pairs
› Bonded atoms: 2 impeding the formation of
this angle, the structure is
› Lone pairs: 0 then linear.
 ANSWER: LINEAR

16.  STEP 1: Draw the Lewis structure
› Remember how many valence electrons the central atom
has (in this example, O)
› Remember the valence electrons the bound atoms have
(the hydrogens) just so you know how the chemical bonds
are being formed.
 The lone pairs of these B atoms don’t determine the molecule’s
structure in this VSEPR model.

17. Two lone
pairs (E) in
atom A
 STEP 2: Count how many (central
atoms have bonded to the atom)
central atom.
› ANSWER: 2
 STEP 3: Count how many
lone pairs the central atom
has Two B atoms

18. Remember the repulsion
between electrons: as each
electron pair repel each
other, they’ll try to be as far
as possible from each other.
 STEP 4: Check the  The two lone pair
VSEPR chart: electrons of the central atom
push the electrons from the
› Total number of bonds; the 180ª degree can
domains (2+2=4) no longer be achieved.
› Bonded atoms: 2
› Lone pairs: 2
 ANSWER: BENT

19.  STEP 1: Draw the Lewis structure
› Remember how many valence electrons the central atom has (in
this example, O)
› Remember the valence electrons the bound atoms have (the other
two oxygens) just so you know how the chemical bonds are being
formed.
 The lone pairs of these B atoms don’t determine the molecule’s
structure in this VSEPR model.
This is a
resonant
molecule

20. One lone
pair (E) in
atom A
 STEP 2: Count how many (central
atoms have bonded to the atom)
central atom.
› ANSWER: 2
 STEP 3: Count how many
lone pairs the central atom
Two B atoms
has

21. Actually, this is a trick
questions:
It has been previously
stated that this is a resonant
molecule
 STEP 4: Check the One can’t
VSEPR chart: successfully draw a
VSEPR model for a
› Total number of resonant molecule.
domains (2+1=3) REAL ANSWER: NO MODEL
› Bonded atoms: 2
› Lone pairs: 1
 ANSWER: BENT?

22.  STEP 1: Draw the Lewis
structure
› Remember how many valence
electrons the central atom has (in
this example, N)
› Remember the valence electrons
the bound atoms have (the
hydrogens) just so you know how
the chemical bonds are being
formed.
 The lone pairs of these B atoms

23. One lone
pair (E) in
atom A
 STEP 2: Count how many (central
atoms have bonded to the atom)
central atom.
› ANSWER: 3
 STEP 3: Count how many
lone pairs the central atom
has Three B
atoms

24. This would be a trigonal
planar with bond angles of 120ª
between each hydrogen if it
weren’t for the nitrogen’s lone
 STEP 4: Check the pair that pushes hydrogen
away. Remember that lone
VSEPR chart: pairs repel bonds as well.
› Total number of
domains (3+1=4)
› Bonded atoms: 3
› Lone pairs: 1
 ANSWER: TRIGONAL
PYRAMID

25.  STEP 1: Draw the Lewis structure
› Remember how many valence
electrons the central atom has (in
this example, C)
› Remember the valence electrons the
bound atoms have (the hydrogens)
just so you know how the chemical
bonds are being formed.
 The lone pairs of these B atoms don’t
determine the molecule’s structure in
this VSEPR model.

26. No lone
pairs in atom
A (central
 STEP 2: Count how many atom)
atoms have bonded to the
central atom.
› ANSWER: 4
 STEP 3: Count how many
lone pairs the central atom
has Four B
atoms

27.  STEP 4: Check the
VSEPR chart:
› Total number of
domains (4+0=4)
› Bonded atoms: 4
› Lone pairs: 0
 ANSWER:
TETRAHEDRAL

28.  STEP 1: Draw the Lewis
structure
› Remember how many valence
electrons the central atom has
(in this example, P)
› Remember the valence
electrons the bound atoms have
(the fluorines) just so you know
how the chemical bonds are
being formed.
 The lone pairs of these B atoms

29. No lone
pairs in atom
A (central
 STEP 2: Count how many atom)
atoms have bonded to the
central atom.
› ANSWER: 5
 STEP 3: Count how many
lone pairs the central atom
has Five B
atoms

30.  STEP 4: Check the
VSEPR chart:
› Total number of
domains (5+0=4)
› Bonded atoms:5
› Lone pairs: 0
 ANSWER: TRIGONAL
BIPYRAMIDAL

31.  STEP 1: Draw the Lewis
structure
› Remember how many valence
electrons the central atom has (in
this example, Cl)
› Remember the valence electrons
the bound atoms have (fluorines)
just so you know how the
chemical bonds are being formed.
 The lone pairs of these B atoms
don’t determine the molecule’s

32. Two lone
pairs (E) in
atom A
 STEP 2: Count how many (central
atom)
atoms have bonded to the
central atom.
› ANSWER: 3
 STEP 3: Count how many
lone pairs the central atom
has Three B
atoms

33. The two lone pairs push the
fluorines away.
NOTE: notice that both
chlorine and fluorine are
halogens. Bonds between
 STEP 4: Check the halogens and noble gases
VSEPR chart: tend to form planar structures.
› Total number of
domains (3+2=5)
› Bonded atoms: 3
› Lone pairs: 2
 ANSWER: T-SHAPED