NH

Molecular Geometry

Page 1:

  • Molecular shapes can be predicted using the VSEPR theory

  • Lewis structures are two-dimensional representations of molecules

  • Molecules are actually three-dimensional

  • The shape of a molecule determines its physical and chemical properties

Page 2:

  • The structures shown in the left-hand column of Model 1 are Lewis Structures

  • A solid line between two element symbols represents a covalent bond

  • The solid lines are made up of electrons

  • A pair of dots represents a lone pair of electrons

  • The dots are also made up of electrons

  • "Domain" means an area within something or someone's control

  • Molecules with four electron domains: H2O, NH3, CH4

  • Molecules with two electron domains: CO2, BeF2

  • Molecule with three electron domains: H2CO

  • When determining the number of electron domains, count bonds and lone pairs on the center atom

Page 3:

  • A bonding electron domain is a bond on the central atom

  • A nonbonding electron domain is a lone pair on the central atom

  • Pairs of electrons repel each other

  • Two bonds on the same atom try to get as far from each other as possible

  • A lone pair of electrons and a bonded pair of electrons push away from each other

  • VSEPR theory is based on the premise that electrons around a central atom repel each other

  • Valence shell electrons are the most critical for determining molecular shape

  • Electrons around the central atom repel each other in VSEPR theory

Page 4:

  • None of the molecular shapes in Model 1 have 90° bond angles

  • The bond angles in three-dimensional molecules are generally larger than those in Lewis structures

  • Three-dimensional molecules have larger angles because electrons have an additional dimension to move away in

  • Molecules with four electron domains: H2O, NH3, CH4

  • As the number of lone pairs on the central atom increases, the bond angle decreases

Page 5:

  • Lewis structure for H2S: H - S - H

  • 3-D drawing: Bent

  • Bond angle: 104.5°

  • Lewis structure for PH3: P - H

  • 3-D drawing: Pyramidal

  • Bond angle: 107°

  • Lewis structure for CCl4: C - Cl

  • 3-D drawing: Tetrahedral

  • Bond angle: 109.5°

  • Lewis structure for CS2: C = S

  • 3-D drawing: Linear

  • Bond angle: 180°

Page 6:

  • Lewis structure for ozone (O3): O = O - O

  • Ozone has a bent shape instead of a linear shape

  • Ozone's bond angle is larger than that of water (H2O) because it has three electron