Unit 9: Molecular Geometry and Bonding Theories

the properties of a molecule depend on…

the shape and nature of the bonds

a model for the geometry of molecules

valence-shell electron-pair repulsion (VSEPR) theory

a model about WHY molecules form bonds and WHY they have the shape they do

valence-bond theory

a model of chemical bonding that deals with the electronic structure of molecules

why they look the way they do

molecular orbital (MO) theory

bond angles

the angles made by the lines joining the nuclei of a molecule’s atoms

connects nucleus between lines

electron domain

a region in which at least two electrons are found

bonds = 1

why do electron domains repel each other?

because they’re negatively charged (optimizes space)

bonding domain

2-6 e- that are shared by TWO atoms, this forms a COVALENT BOND

nonbonding domain

2 e- that are located on a single atom; aka a LONE PAIR

VSEPR for NH3

(ammonia); 3 bonding domains, 1 nonbonding domain = 4 e- domains

how do domains arrange themselves?

so as to minimize their repulsions—they’re always pushing(b/c they’re all negative)

electron-domain geometry

one of five basic arrangements of domains

depends only on the total # of e- domains not the kind of domain

overall # of domains

molecular geometry

describes the orientation of the atoms in space

depends on how many of each kind of e- domain

depends on TYPES of domains

to find the EDG and/or MG….

draw the LS

multiple bonds count as single domain

total number of domains:

electron-domain geometry:

possible Molecular geometries:

2; linear; linear (e.g: CO2)

molecules with more than one central atom…. (predicting the EDG and MG)

apply the VSEPR model to each individual/part

nonbonding domains are attracted to…

only ONE nucleus

are more spread out

i.e. “lone pairs”

COMPRESS bond angles—pushes on other bonds because its not really bonded, causes fluctuation in IBA

bonding domains are…

less spread out

a molecules polarity is determined by…

its overall dipole, which is the vector sum of the dipoles of each of the molecule’s bonds

total # of domains: 3

electron-domain geometry:

possible Molecular Geometries:

IBA:

trigonal planar;

all 3 bonding: trigonal planar (e.g BF3)

1 nonbonding: bent (e.g. NO2)

120

total # of domains: 4

EDG:

possible MG:

IBA:

tetrahedral

all 4 bonding: tetrahedral (e.g CH4)

2 non bonding