9 - Molecular Structures - Chapter 9: Molecular Structures...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 9: Molecular Structures 9.1 Using Molecular Models space-filling model are scaled according to experimental values for atom sizes solid wedges are used to represent bonds extending in front of page dashed lines or dashed wedges are used to represent bonds behind the page 9.2 Predicting Molecular Shapes: VSEPR valence-shell electron-pair repulsion (VSEPR) model – predict shapes of molecules and polyatomic ions; repulsions occur among regions of electron density (i.e., bonding pairs, lone pair electrons) and control angles between bonds electron pairs move as far apart as possible to minimize repulsion Central Atoms with Only Bonding Pairs o electron-pair geometry – number and arrangement of electron pairs around central atom o molecular geometry – arrangement of atoms in space o if molecules whose central atoms have no lone pairs, then electron-pair geometry and molecular geometry are the same o bond angles – angles between bonds of two atoms that are bonded to the same third atom Type Electron-Pair Geometry Molecular Geometry Example AX 2 E 0 Linear Linear CO 2 AX 2 E 1 Triangular planar Angular (bent) SnCl 2 AX 2 E 2 Tetrahedral Angular (bent) H 2 O AX 2 E 3 Triangular bipyramidal Linear XeF 2 AX 3 E 0 Triangular planar Triangular planar BCl 3 AX 3 E 1 Tetrahedral Triangular pyramidal NCl 3 AX 3 E 2 Triangular bipyramidal T-shaped ClF 3 AX 4 E 0 Tetrahedral Tetrahedral CH 4 AX 4 E 1 Triangular bipyramidal Seesaw SF 4 AX 4 E 2 Octahedral Square planar XeF 4 AX 5 E 0 Triangular bipyramidal Triangular bipyramidal PF 5 AX 5 E 1 Octahedral Square pyramidal BrF 5 AX 6 E 0 Octahedral Octahedral SF 6 Multiple Bonds and Molecular Geometry o double and triple bonds are shorter and stronger but don’t affect molecular shape because they are shared between the same atoms and occupy the same region of space as a single bond would Central Atoms with Bonding Pairs and Lone Pairs o 1) draw Lewis structure o 2) determine number of bonds and number of lone pairs around each atom o 3) pick appropriate electron-pair geometry around each central atom and then choose molecular shape that matches total number of bonds and lone pairs o 4) predict bond angles, lone pairs occupy more volume than bonding pairs; lone pair-lone pair > lone pair-bonding pair > bonding pair-bonding pair Expanded Octets: Central Atoms with Five or Six Electron Pairs o triangular bipyramidal does not have equal bond angles; 90 degrees in axial positions (north and south), and 120 degrees in equatorial positions (triangular plane) axial positions are next to three electron pairs at 90 degrees while equatorial positions are next to two axial electron pairs at 90 degrees which means that lone pairs will occupy equatorial positions
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/28/2009 for the course CHEM 1A taught by Professor Nitsche during the Fall '08 term at University of California, Berkeley.

Page1 / 4

9 - Molecular Structures - Chapter 9: Molecular Structures...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online