VESPR

VESPR

Molecules will adopt a shape that is lowest in energy

A low energy shape is one that minimizes the valence shell electron pair repulsion (VSEPR) between adjacent atoms

What does this mean?

atoms try to spread out to reduce the "like charge repulsion" between outer electrons.

Methane CH4

This causes less repulsion between bonding pairs of electrons because they are 109.5 degrees apart

5 main shapes of molecular geometry

linear: 180 degrees

Trigonal Planar: 120 degress

Tetrahedral: 109.5

Trigonal Bipyramid: 90, the 120

Octahedral: 90

Linear molecular geometry

Bond Angle: 180

Molecular Geometry: linear

Domain (electron pair sites): 2

Number of bonding sites: 2

Number of lone pair electrons: 0

Trigonal Planar

Bond angle: 120

Molecular Geometry: trigonal planar

Domain: 3

Bonding Sites: 3

Lone pair: 0

Trigonal Planar (Bent)

Bond angle: 120

Molecular Geometry: trigonal planar

Domain: 3

Bonding Sites: 2

Lone pair: 1

Tetahedral

Bond angle: 109.5

Molecular Geometry: tetrahedral

Domain: 4

Bonding Sites:4

Lone pair: 0

Tetrahedral (Bent)

Bond angle: 109.5

Molecular Geometry: tetrahedral

Domain: 4

Bonding Sites: 2

Lone pair: 2

Tetrahedral Trigonal Pyramidal

Bond angle: 109.5

Molecular Geometry: tetrahedral

Domain: 4

Bonding Sites: 3

Lone pair: 1

Trigonal Bipyramidal

Bond Angle: 120 +90

Molecular Geometry: Trigonal Bipyramidal

Domain: 5

Bonding Sites: 5

Lone pair: 0

Trigonal Bipyramidal (Seesaw)

Bond Angle: 117 +90

Molecular Geometry: Seesaw

Domain: 5

Bonding Sites: 4

Lone pair: 1

Trigonal Bipyramidal (T-Shaped)

Bond Angle: 90

Molecular Geometry: T-shaped

Domain: 5

Bonding Sites: 3

Lone pair: 2

Trigonal Bipyramidal (Linear)

Bond Angle: 120 +90

Molecular Geometry: Trigonal Bipyramidal

Domain: 5

Bonding Sites: 5

Lone pair: 0

Octahedral

Bond Angle: 90

Molecular geometry: Octahedral

Domain: 6

Bonding sites: 6

Lone Pair: 0

Square Pyramidal Octahedral

Bond Angle: 90

Molecular geometry: Square Pyramidal

Domain: 6

Bonding sites: 5

Lone Pair: 1

Square Planar Octahedral

Bond Angle: 90

Molecular geometry: square planar

Domain: 6

Bonding sites: 4

Lone Pair: 2

Steps for determining molecular geometry

1. draw Lewis dot structure

2. count number of bonds and lone pairs (domains)

Single,double, triple bonds and lone pair count as one domian

3. use chart to find shape

name of molecule is based on position of atoms (not domains)

Domain

region where electrons are likely to be, area of high electron concentration

bonds=bonding domains

lone pair=nonbonding domains

Domains (pt2)

negatively charged so they want to be as far apart. This minimizes :like charge repulsion" and is the lowest possible energy state

Lone pairs

take up more space than bonding pairs and thus push atoms farther away from each other

VESPR

"AXE"

A= central atom

X= number of atoms bonded to central atom (have subscript to state how many)

E= number of lone pair electrons on central atom (subscript)

Fisher Projections

a way to make your Lewis structures seem 3D on paper

polar covalent

two atoms don't share electrons equally. Electrons are pulled closer to the more electronegative atom which then one end of the molecule develops a partial negative charge b/c it has higher electron density

Dipole Moments

a molecule having an area of partial positive charge and area of partial negative

example: HCL

Dipole Moments (pt2)

ALL diatomic molecules with a polar bond have dipole moment

SOME polyatomic molecules with polar have dipole moment

(water does carbon dioxide doesn't it depends on molecular geometry)

Water

Polar (H-O bonds)

geometry is "bent"

molecule is polar (has a dipole)

BF3 is non-polar

Has polar B-F bonds

geometry is "trigonal planar"

So the molecule is no polar (it doesn't have a dipole and all flourines "cancel")

"Like dissolves like"

Polar molecules dissolve in polar solvents

Nonpolar molecules dissolve in nonpolar solvents

polar and nonpolar dont mix

(oil: nonpolar, water:polar)

Hydrogen Bonds

bonds with N, O, F

bonding occurs b/w adjacent molecule covalent polar molecules

Dipole-Dipole

attractive forms between 2 opposite poles of 2 polar molecules

Dispersion

Because 2 nonpolar molecules attractive forces caused by movement of electrons

Create a temporary dipole