AP Chem: VSEPR Theory: Valence Shell Electron Pair Repulsion Theory : Determines the shape of
molecules using the number of electron groups around a central atom. (A Double or Triple bond counts
as 1 bonding group in this chart).
Total e– Electron Pair
groups Geometry
2
Linear
–X–
Bonding Nonbond. Molecular
e– groups e– groups Geometry
Example
Hybridization of
Central Atom
O=C=O
2 sp
hybrids
2
0
Linear
2
1
Bent
3
0
Trigonal
Planar
F
|
B
/ \
F" F
2
2
Bent
˙˙
O
/ ˙˙ \
180° angle
3
Trigonal
planar
|
X
/\
120° angles
4
Tetrahedral
|
X
/|\
H
1
Trigonal
Pyramidal
4
0
Tetrahedral
2
3
Linear
˙˙
F–" ˙˙
Xe–F
..
Trigonal
Bipyramidal
3
2
T shaped
\ /
–X– 90°
|
120°
4
1
Seesaw
F–˙˙Cl˙˙–F
!|
F
F
\ ..
F– S –F
|
F
5
0
Cl Cl
Trigonal
\/
Bipyramidal Cl –P–Cl
|
Cl
4
2
Square
Planar
|/
–X–
/|
(All 90°)
like xyz
" axes
5
1
Square
Pyramidal
6
0
Octahedral
3 sp2 1 double bond
possible
hybrids (1 ! bond)
no double or
4 sp3
hybrids triple bonds
possible
˙˙
N
/|\
H H H
H
|
C
/ | \
H H H
3
Octahedral
6
// \
O O
H
109° angles
5
˙˙
N –
1 triple or 2
double bonds
possible
(2 ! bonds)
F"
|..
F– Xe –F
˙˙|
F
F F
|/
F– Br –F
/!˙˙
F
F F
|/
F– S –F
/|
F F"
double or
5 sp3d no
triple bonds
hybrids possible
double or
6 sp3d2 no
triple bonds
hybrids possible
Energies for Born Haber cycle calculations (Ionic compounds)
Ionization Energy (kJ/mol)
"
1st"
2nd" 3rd
Li"
520" 7297" 11810
Na" 496" 4560" 6912
K"
419" 3050" 4420
Mg" 738" 1450" 7733
Ca"
590" 1145" 4912
Cr"
653" 1592" 2987
Cu" 745" 1958" 3555
Fe"
792" 1561" 2957
Hg" 1000" 1809" 3300
Ni"
737" 1756" 3397
Ti"
658" 1312" 2654
Zn"
906" 1733" 3833
Electron Affinities
(First electron)
"
(kJ/mol)
F"
–332
Cl"
–349
Br"
–325
I"
–295
O"
–142
S"
–202
Approx Lattice energy"
(kJ/mol)
LiF"
1024"
NaF"
911
LiCl"
853"
NaCl "
788
LiBr"
807"
NaBr"
747
LiI"
757"
NaI"
704
KF"
815"
MgF2"
2910
KCl"
715"
MgCl2 "
2526
KBr"
682"
CaCl2 "
2200
KI"
649"
SrCl2 "
2130
Na2O"
2481"
MgO"
3791
The following are estimated
CrCl3"
5500"
HgCl3"
5000
CrF3"
6000"
NiI3"
5100
CuF3"
5600"
TiBr3"
5000
FeBr3"
5300"
ZnI3 "
5200
NaCl2 " 2500"
KI2"
1900
Bond Energies (kJoule/mol of bonds) (Gaseous molecules only)
Bond
Energy
Bond
Energy
Bond
Energy
H–H"
436
C – C"
348
H – C"
413
O – O"
146
C = C"
614
H – N"
391
O = O"
495
C ≡ C"
839
H – O"
463
F – F"
155
N – N"
163
H – F"
567
Cl – Cl"
242
N = N"
418
H – Cl "
431
Br – Br "
193
N ≡ N"
941
H – Br"
366
I – I"
151
H – I"
299
N ≡ C"
891
N–Cl"
193
Bond
C–F"
C – Cl"
C – Br"
C – I"
C = N"
C – O"
C = O"
C ≡ O"
Energy
485
328
276
240
615
358
799
1072
Breaking bonds between atoms always absorbs energy. Making bonds between atoms always releases energy.
Endothermic = + ∆H (bonds in products are “less stable” than bonds in reactants)
" "
or... the reaction absorbs more energy to break bonds than it releases to make new bonds
Exothermic = – ∆H (bonds in products are “more stable” than bonds in reactants)
" "
or... the reaction releases more energy making new bonds than it absorbs to break bonds
Determining ∆H for a reaction using Bond energies:
∆Hreaction = Bonds broken – Bonds made (Estimate, gaseous reactions only)
Molecular Polarity:
Non-Polar = “all alike”: no + or – end: same elements, same element around a symmetrical shape, all
C’s and H’s, or with N’s or O’s in the middle of a hydrocarbon chain. (tetrahedral, linear, trig. planar)
Polar = “Different”: has a + end and a – end: different elements around center, even if symmetrical
shape or non-symmetrical shape, O’s or N’s “sticking out” of a hdrocarbon chain. (bent, trig pyramid)