CREATE "In this tutorial we will investigate the shapes of simple covalent molecules Specifically, we will be learning about something called VSEPR theory and how it allows us to predict the shapes that covalently bonded molecules will have."

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Molecular Geometry H H H H o C Linear Trigonal planar Tetrahedral Trigonal pyramidal Bent o o o H 2 O CH 4 AsCl 3 AsF 5 BeH 2 BF 3 CO o

C o H H H H N 107 o H H H.. O o H H.. CH 4, methaneNH 3, ammoniaH 2 O, water.. O O O lone pair electrons O OO O 3, ozone

Molecular Shapes Three atoms (AB 2 )Four atoms (AB 3 ) Five atoms (AB 4 ) Six atoms (AB 5 ) Seven atoms (AB 6 ) Linear (180 o ) Bent Trigonal planar (120 o ) Trigonal pyramidal T-shaped Tetrahedral ( o ) Square planar Seesaw Trigonal bipyramidal (B e AB e, 120 o ) & (B e AB a, 90 o ) Square pyramidal Octahedral BBA B B A B lineartrigonal planar B A B B B tetrahedral A BeBe BeBe BeBe BaBa BaBa Trigonal bipyramidal B B B B B B A Bailar, Moeller, Kleinberg, Guss, Castellion, Metz, Chemistry, 1984, page 313.

Bonding and Shape of Molecules Number of Bonds Number of Unshared Pairs ShapeExamples Linear Trigonal planar Tetrahedral Pyramidal Bent BeCl 2 BF 3 CH 4, SiCl 4 NH 3, PCl 3 H 2 O, H 2 S, SCl 2 -Be- B C N : O : : Covalent Structure

Molecular Shapes AB 2 Linear AB 3 Trigonal planar AB 4 Tetrahedral AB 5 Trigonal bipyramidal AB 6 Octahedral AB 2 E Angular or Bent AB 3 E Trigonal pyramidal AB 2 E 2 Angular or Bent AB 4 E Irregular tetrahedral (see saw) AB 3 E 2 T-shaped AB 2 E 3 Linear AB 6 E Square pyramidal AB 5 E 2 Square planar

V alence S hell E lectron P air R epulsion Theory Planar triangular Tetrahedral Trigonal bipyramidal Octahedral

.. The VSEPR Model OO C Linear The Shapes of Some Simple AB n Molecules OO S Bent OO S O Trigonal planar F F F N Trigonal pyramidal T-shapedSquare planar FF Cl F F F Xe FF F F F P F F Trigonal bipyramidal Octahedral F F F S F F F SF 6 SO 2 Brown, LeMay, Bursten, Chemistry The Central Science, 2000, page 305

Molecular Shapes AB 2 Linear AB 3 Trigonal planar AB 4 Tetrahedral AB 5 Trigonal bipyramidal AB 6 Octahedral AB 2 E Angular or Bent AB 3 E Trigonal pyramidal AB 2 E 2 Angular or Bent AB 4 E Irregular tetrahedral (see saw) AB 3 E 2 T-shaped AB 2 E 3 Linear AB 5 E Square pyramidal AB 4 E 2 Square planar

Geometry of Covalent Molecules AB n, and AB n E m AB 2 AB 2 E AB 2 E 2 AB 2 E 3 AB 3 AB 3 E AB 3 E 2 AB 4 AB 4 E AB 4 E 2 AB 5 AB 5 E AB Linear Trigonal planar Tetrahedral Trigonal bipyramidal Trigonal planar Tetrahedral Triangular bipyramidal Tetrahedral Triangular bipyramidal Octahedral Triangular bipyramidal Octahedral Linear Angular, or bent Linear Trigonal planar Triangular pyramidal T-shaped Tetrahedral Irregular tetrahedral (or “see-saw”) Square planar Triangular bipyramidal Square pyramidal Octahedral CdBr 2 SnCl 2, PbI 2 OH 2, OF 2, SCl 2, TeI 2 XeF 2 BCl 3, BF 3, GaI 3 NH 3, NF 3, PCl 3, AsBr 3 ClF 3, BrF 3 CH 4, SiCl 4, SnBr 4, ZrI 4 SF 4, SeCl 4, TeBr 4 XeF 4 PF 5, PCl 5 (g), SbF 5 ClF 3, BrF 3, IF 5 SF 6, SeF 6, Te(OH) 6, MoF 6 Type Formula Shared Electron Pairs Unshared Electron Pairs Ideal Geometry Observed Molecular ShapeExamples Bailar, Moeller, Kleinberg, Guss, Castellion, Metz, Chemistry, 1984, page 317.

Predicting the Geometry of Molecules Lewis electron-pair approach predicts number and types of bonds between the atoms in a substance and indicates which atoms have lone pairs of electrons but gives no information about the actual arrangement of atoms in space Valence-shell electron-pair repulsion (VSEPR) model predicts the shapes of many molecules and polyatomic ions but provides no information about bond lengths or the presence of multiple bonds

Introduction to Lewis Structures Lewis dot symbols 1. Used for predicting the number of bonds formed by most elements in their compounds 2. Consists of the chemical symbol for an element surrounded by dots that represent its valence electrons 3. A single electron is represented as a single dot

Lewis Structures 1) Count up total number of valence electrons 2) Connect all atoms with single bonds - “multiple” atoms usually on outside - “single” atoms usually in center; C always in center, H always on outside. 3) Complete octets on exterior atoms (not H, though) 4) Check - valence electrons math with Step 1 - all atoms (except H) have an octet;if not, try multiple bonds - any extra electrons?Put on central atom