W hat is it anyw ay?
▪ The specific three dimensional arrangement of atoms in molecules is referred to as molecular geometry.
• Molecular geometry can also be defined as the positions of the atomic nuclei in a molecule.
VSPER
▪ V: Valence
▪ S: Shell
▪ E : Electron
▪ P: Pair
▪ R: Repulsion theory
D iff erent bonds r a e Lin
Trigonal bipyramidal Squ pla are nar Pentagonal bipyramid al
Cubic
Tetrahedr al Tetragonal
Pyramidal
Octahedral
Trian gula r
▪These are molecules that only have paired electrons around the central atom!
Linear
• Z ero pai lone r (un s pai shared rs) ms o er t t a n e o c to
▪ Tw d e h attac point Bond angle = 180⁰
Type: AB2
Ex. : BeF2
Tetrahedral
Ze
(un ro lo sha ne p red air pa s irs )
s o m o a t hed t
4
▪ c atom a t t a ter cen Bond angle = 109.5⁰
Type: AB4
Ex. : CH4
TrigonalBipyram idal
Ze
(u ro p a n s lo irs ha ne
) red pa i s oa m o t t a d e ▪ 5 tach tom at ter a cen Bond angle = equatorial -> 120⁰ axial -> 90⁰
Type: AB5
Ex. : PF5
rs
O ctahedral
Ol
(un one p pai shar airs rs) ed
ed h ac m t t a a to s r m e o t t en a ▪ 6oac t Bond angle = 90⁰
Type: AB6
Ex. : SF6
▪These are molecules with both paired and unshared (lone) pairs of electrons around the central
Triangular d e h tac t a s om m t o a t r a ▪ 3 cente to 1 pa lon ir e
Bond angle = 107⁰
Type: AB3E
Ex. : NH3
Predicting the G eom etry of M olecules
• Lewis electron-pair approach predicts number and types of bonds between the atoms in a substance and indicates which atoms have lone pairs of electrons but gives no information about the actual arrangement of atoms in space
• Valence-shell electron-pair repulsion
(VSEPR) model predicts the shapes of many molecules and polyatomic ions but provides no information about bond lengths or the presence of multiple bonds
Lew is Structures
1) Count up total number of valence electrons
2) Connect all atoms with single bonds
- “multiple” atoms usually on outside
- “single” atoms usually in center;
C always in center,
H always on outside.
(not H, though)
3) Complete octets on
