Molecular Geometry and 3D Structures of Molecules

Methane Lewis Dot Structure H H C H H

Sites on an atom • A site is something that takes up space around the atom.

• Attached atoms • Unshared pairs of electrons • Total sites = attached atoms + unshared pairs

H H C Sites in Methane H • Carbon is central atom • 4 atoms (H) attached • no unshared pairs • sites = 4 + 0 = 4 • 4 sites H

VSEPR Theory • Electrons repel • Will move as far apart as possible in 3 dimensions • Actually electron clouds that repel.

• Attached atoms positioned by repulsion of electrons clouds bonded to.

Methane Summary • clouds arrange tetrahedrally • clouds 109.5

o apart • Shape is tetrahedral

Methane ball and stick

3D representation of methane • Wedge is coming out of plane of paper • dash behind • compare to ball and stick

Comparison of Methane Structures

Space filling model of methane

Summary sheet Ex. att. atoms unsh. pairs sites clouds shape angle CH 4 4 0 4 tet.

tet. 109.5

Ammonia Lewis Dot Structure H N H H

H Sites in Ammonia N H • 3 attached atoms • 1 unshared pair • total of 4 sites • Clouds tetrahedral H

Ammonia Ball and Stick

3D Representation of Ammonia • Clouds still tetrahedral • one cloud has unshared pair – invisible cloud – repels more strongly than bonds – pushes bonds together • bond angle 107.7

• trigonal pyramidal

Comparison of Ammonia Structures

Ammonia space fill

Summary sheet Ex. att. atoms unsh. pairs sites clouds shape angle CH 4 4 0 4 tet tet 109.5 NH 3 3 1 4 tet trig. pyr 107.7

Water Lewis Dot Structure H O H

H O Sites in Water • 2 attached atoms • 2 unshared pairs • 4 sites • Clouds tetrahedral H

Water Ball and Stick

H 3D Representation of Water O H • Clouds still tetrahedral • two clouds have unshared pairs – invisible clouds – repel more strongly than bonds – push bonds together • bond angle 105 • bent

Comparison of Water Structures H O H

Water Space Fill

Summary sheet Ex. CH 4 NH 3 att. atoms 4 unsh. pairs 0 3 1 sites 4 4 H 2 O 2 2 4 clouds shape angle tet tet tet tet trig. pyr bent 109.5 107.7 105

HCl Lewis Dot Structure H Cl

H Sites in HCl Cl • 1 attached atom • 3 unshared pairs • 4 sites • Clouds tetrahedral

HCl Ball and Stick

H 3D Representation of HCl Cl • Clouds still tetrahedral • three clouds have unshared pairs – invisible clouds • bond angle 180 • linear

Comparison of HCl Structures H Cl

HCl Space Fill

Ex. CH 4 NH 3 H 2 O HCl 3 2 1 Summary sheet sites att. atoms 4 unsh. pairs 0 4 clouds shape angle tet tet 109.5 1 2 3 4 4 4 tet tet tet trig. pyr 107.7 bent 105 linear 180

CH 2 O Lewis Dot Structure O H C H

Sites in CH 2 O H O C H • 3 attached atoms • 0 unshared pairs • 3 sites • Clouds trigonal planar

CH 2 O Ball and Stick

H 3D Representation of CH 2 O O • clouds go to corners of equilateral triangle • bond angle 120 • trigonal planar C H

Comparison of CH 2 O Structures O H C H Since planar, both structures are the same.

CH 2 O Space Fill

Ex. CH 4 NH 3 H 2 O HCl 2 1 CH 2 O 3 Summary sheet att. atoms 4 unsh. pairs 0 3 1 sites 4 4 2 3 0 4 4 3 clouds shape angle tet tet 109.5 tet tet tet trig. planar trig. pyr 107.7 bent 105 linear 180 trig. planar 120

SO 2 Lewis Dot Structure O S + O

Sites in SO 2 O S + O • 2 attached atoms • 1 unshared pairs • 3 sites • Clouds trigonal planar

SO 2 Ball and Stick

O 3D Representation of SO 2 S + • Clouds go to corners of equilateral triangle – unshared pair is invisible cloud • bond angle between 105 and 120 • bent O

Comparison of SO 2 Structures O S + O Since bent, both structures are the same.

SO 2 Space Fill

Ex. CH 4 NH 3 H 2 O HCl 2 1 CH 2 O 3 SO 2 2 Summary sheet clouds shape angle att. atoms 4 unsh. pairs 0 3 1 sites 4 4 2 3 0 1 4 4 3 3 tet tet tet tet trig trig tet 109.5 trig. pyr 107.7 bent 105 linear 180 trig. planar 120 bent <120

SO 2 Lewis Dot Structure…Double bonded oxygen O S + O

Sites on O in SO 2 O S + O • 1 attached atoms • 2 unshared pairs • 3 sites • Clouds trigonal planar

O 3D Representation of SO 2 S + • Clouds go to corners of equilateral triangle – unshared pairs are invisible clouds • bond angle 180 • linear around double bound oxygen O

Comparison of SO 2 Structures O S + O Linear around double bonded O

Ex. CH 4 NH 3 SO 2 O in SO 2 Summary sheet clouds shape angle att. atoms 4 unsh. pairs 0 3 1 sites 4 4 H 2 O HCl 2 1 CH 2 O 3 2 1 2 3 0 1 2 4 4 3 3 3 tet tet tet tet trig trig trig tet 109.5 trig. pyr 107.7 bent 105 linear 180 trig. planar 120 bent <120 linear 180

CO 2 Lewis Dot Structure O C O

Sites in CO 2 O C O • 2 attached atoms • 0 unshared pairs • 2 sites • Clouds linear

CO 2 Ball and Stick

O 3D Representation of CO 2 • Clouds linearly arranged.

• bond angle 180 • linear C O

Comparison of CO 2 Structures O C O Since linear, both structures are the same.

CO 2 Space Fill

Ex. CH 4 NH 3 H 2 O HCl 2 1 CH 2 O 3 SO 2 O in SO 2 CO 2 2 1 2 Summary sheet clouds shape angle att. atoms 4 unsh. pairs 0 3 1 sites 4 4 2 3 0 1 2 0 4 4 3 3 3 2 tet tet tet tet trig trig trig tet 109.5 trig. pyr 107.7 bent 105 linear 180 trig. planar 120 bent <120 linear 180 linear linear 180

N 2 Lewis Dot Structure N N

N Sites in N 2 N • 1 attached atom • 1 unshared pair • 2 sites • Clouds linear

N 2 Ball and Stick

N 3D Representation of N 2 • Clouds linearly arranged.

• bond angle 180 • linear N

Comparison of N 2 Structures N N Since linear, both structures are the same.

N 2 Space Fill

Ex. CH 4 NH 3 H 2 O HCl 2 1 CH 2 O 3 SO 2 O in SO 2 CO 2 N 2 2 1 2 1 Summary sheet clouds shape angle att. atoms 4 unsh. pairs 0 3 1 sites 4 4 2 3 0 1 2 0 1 4 4 3 3 3 2 2 tet tet tet tet trig trig trig tet 109.5 trig. pyr 107.7 bent 105 linear 180 trig. planar 120 bent <120 linear 180 linear linear 180 linear linear 180