VSEPR T HEORY Valence Shell Electron Pair Repulsion

VSEPR T HEORY Predicts the molecular shape of a bonded molecule Electrons around the central atom arrange themselves as far apart from each other as possible Unshared pairs of electrons (lone pairs) on the central atom repel the most So only look at what is connected to the central atom

6 T YPES OF M OLECULES WITH NO U NSHARED P AIRS OF E LECTRONS

L INEAR 2 atoms attached to central atom 0 unshared pairs (lone pairs) Bond angle = 180 o Type: AB 2 Ex. : BeF 2

3 EXCEPTIONS TO THE OCTET RULE Molecules with an odd number of electrons Molecules with atoms near the boundary between metals and nonmetals will tend to have less than an octet on the central atom. (i.e. B, Be, Al, Ga) Molecules with a central atom with electrons in the 3 rd period and beyond will sometimes have more than an octet on the central atom, up to 12, called an extended or expanded octet.

L INEAR Carbon dioxide CO 2

T RIGONAL P LANAR 3 atoms attached to central atom 0 lone pairs Bond angle = 120 o Type: AB 3 Ex. : AlF 3

T RIGONAL P LANAR Boron Trifluoride BF 3

T ETRAHEDRAL 4 atoms attached to central atom 0 lone pairs Bond angle = o Type: AB 4 Ex. : CH 4

T ETRAHEDRAL Carbon tetrachloride CCl 4

T RIGONAL B IPYRAMIDAL 5 atoms attached to central atom 0 lone pairs Bond angle = equatorial -> 120 o axial -> 90 o Type: AB 5 Ex. : PF 5

T RIGONAL B IPYRAMIDAL Antimony Pentafluoride SbF 5

O CTAHEDRAL 6 atoms attached to central atom 0 lone pairs Bond angle = 90 o Type: AB 6 Ex. : SF 6

O CTAHEDRAL Sulfur hexafluoride SF 6

E XAMPLES OF M OLECULES WITH B OTH P AIRED AND U NSHARED ( LONE ) P AIRS OF E LECTRONS AROUND THE C ENTRAL A TOM.

T ETRAHEDRAL Carbon tetrachloride CCl 4

T RIGONAL P YRAMIDAL Tetrahedral variation #1 3 atoms attached to central atom 1 lone pair Bond angle = 107 o Type: AB 3 E Ex. : NH 3

T RIGONAL P YRAMIDAL Nitrogen trifluoride NF 3

B ENT Tetrahedral variation #2 2 atoms attached to central atom 2 lone pairs Bond angle = o Type: AB 2 E 2 Ex. : H 2 O

B ENT Chlorine difluoride ion ClF 2 +

T RIGONAL B IPYRAMIDAL Antimony Pentafluoride SbF 5

S EE S AW Trigonal Bipyrimid Variation #1 Sulfur tetrafluoride SF 4

T-S HAPED Trigonal Bipyramid Variation #2 Chlorine tribromide

L INEAR Trigonal Bipyramid Variation #3 Xenon difluoride XeF 2

O CTAHEDRAL Sulfur hexafluoride SF 6

S QUARE P YRAMIDAL Octahedral Variation #1 Chlorine pentafluoride ClF 5

S QUARE P LANAR Octahedral Variation #2 Xenon tetrafluoride XeF 4

O CTAHEDRAL Do not need to know: T-shape Linear

B ENT Nitrogen dioxide NO 2