# Molecular Geometry  3-D arrangement of molecules.

## Presentation on theme: "Molecular Geometry  3-D arrangement of molecules."— Presentation transcript:

Molecular Geometry  3-D arrangement of molecules

VSEPR Theory  Valence-shell, electron-pair repulsion  Def: repulsion b/ valence e - pairs around atom causes them to be as far apart as possible

Shapes  NO lone pairs on CENTRAL atom  Symmetrical  Linear  Trigonal-Planar  Tetrahedral  Trigonal- bipyramidal  Octahedral  WITH lone pairs on CENTRAL atom  Non- symmetrical  Trigonal-pyramidal  Bent (angular)

Shapes – NO lone pairs on central atom 1. Linear (AB 2 ): A – central atom B-bonded atoms - 3 atom molecules CO 2 - 2 atom molecules, O 2, HCl, etc. - bond angles: 180 o

Shapes – NO lone pairs on central atom 2. Trigonal Planar (AB 3 ): - BCl 3 - bond angles: 120 o

Shapes – NO lone pairs on central atom 3. Tetrahedral (AB 4 ): - CCl 4 - bond angles: 109.5 o

Shapes – NO lone pairs on central atom 4. Trigonal-bipyramidal (AB 5 ): - PCl 5 - bond angles: 120 o and 90 o

Shapes – NO lone pairs on central atom 5. Octahedral (AB 6 ): - SF 6 - bond angles: 90 o

Shapes – WITH lone pairs on central atom 6. Trigonal-Pyramidal (AB 3 E): A – central atom B – bonded atoms E – lone pair - NH 3 - triangular sides - bond angles: 107 o

Shapes – WITH lone pairs on central atom 7. Bent or Angular (AB 2 E 2 ): - H 2 O - bond angles: 105 o

Molecular Polarity  Polarity of each bond  Molecular polarity

Molecular Polarity 1. Has ALL bonds NONPOLAR  nonpolar molecule 2. Has bonds nonpolar AND polar  polar molecule 3. Has ALL bonds POLAR  depends on shape Symmetrical shape (linear - octahedral)  NONPOLAR Non-symmetrical shape (bent & trigonal pyramidal)  POLAR

Molecular Polarity Examples  CCl 4  PH 3  CBr 3 H

Intermolecular Forces

 “between molecule” forces  Generally weaker than bonds b/ atoms  Boiling point – good to measure intermolecular forces

Dipole-Dipole Forces  Dipole- equal but opposite charges separated by a short distance  Video 124

Dipole-Dipole Forces  Induced Dipole: polar molecule makes a dipole on a nonpolar molecule  Ex: O 2 dissolved in H 2 O  Weaker than regular dipole forces

Hydrogen Bonding  Type of dipole-dipole force  Def: H-atom bonded to highly e - neg atom is attracted to lone pair of the e - neg atom in nearby molecule  Ex: HF, H 2 O, NH 3

Hydrogen Bonding

London Dispersion Forces  Def: constant motion of e - s and creation instantaneous dipoles  Video 133