Ch 10 - Ch. 10: Chemical Bonding II: Molecular Shapes,...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
Ch. 10: Chemical Bonding II: Molecular Shapes, Valence Bond Theory, Molecular Orbital Theory A. Electronic Geometry a. electronic geometry = 3D arrangement of electron regions around central atom; a.i. 2 = linear (180°) a.ii. 3 = trigonal planar (piece-sign, but in lewis structure: straight line with 3 rd atom on top of central atom) a.iii. 4 = tetrahedral (lewis: equally into 4) a.iv. 5 = trigonal bipyramidal (Lewis structure: pentagonal) a.v. 6 = octahedral (lewis structure: hexagonal) b. VSEPR: Valence Shell Electron-Pair Repulsion b.i. VSEPR theory : electron pairs around central atom repel each other, affecting geometrics/shapes of molecules b.i.1. ex. CH 4 : tetrahedral—4 outer H-atoms spaced 109.5° from each other b.i.2. NH 3 : 3 outer atoms, oen lone pair; bond angles are 107°; magnitude of repulsion b/w lone pair + bonded pair = greater than repulsion b/w bonded pair and bonded pair b.i.3. H 2 O = two outer atoms + 2 lone pairs, has tetrahedral electronic geometry too with 105° b/w bond angles b.i.3.a. thus, magnitude of repulsion: Lone pairs – lone pairs > lone pairs – bond pairs > bond pairs – bond pairs b.ii. shape/bond angles of a molecule can be predicted by VSEPR; Outer atoms Lone pairs Charge clouds Shape 2 0 2 linear 3 0 3 trigonal planar 2 1 3 bent 4 0 4 tetrahedral 3 1 4 trigonal pyramidal 2 2 4 bent 5 0 5 trigonal bipyramidal 4 1 5 seesaw 3 2 5 T-shaped 2 3 5 linear 6 0 6 octahedral 5 1 6 square pyramidal 4 2 6 square planar c. 10.3 Applying VSEPR Model c.i. Draw Lewis structure c.ii. Count the # of electron groups that central atom has to find electron geometry (e- groups being any lone pairs, and any electrons bonded to other atoms)
Background image of page 1

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

View Full DocumentRight Arrow Icon
c.ii.1. 2= linear, 3 = trigonal planar, 4= tetrahedral, 5 = trigonal bipyramidal, 6= octahedral) c.ii.2. if no lone pairs, then electron geometry = molecular geometry c.iii. Arrange lone pairs as far apart as possible c.iv. Molecular geometry (p. 408) is given by positions of atoms only, so ignore lone pairs c.v. Some examples: c.v.1. SF 4 –5 electron groups trigonal bipyramidal c.v.1.a. the planes that are flat (latitude) = equatorial; longitude = axial (think of the earth) c.v.1.b. there’s one lone pair on S; put it on equatorial for trigonal bipyramidal b/c there’s a 120° diff vs. 90° on axial… c.v.1.b.i. 3 90° angles on axial, only 2 on equatorial c.v.1.c. see-saw shape c.v.2. XeF 2 c.v.2.a. 3 lone pairs, they go around equator, and F are on top and bottom c.v.3. BrF 5 c.v.3.a. 1 lone pair on Br, actually doesn’t matter where u put the lone pair b/c wherever you put it, it’d be the same 90°; (for octahedrals ) c.v.3.b. molecular geometry = square pyramidal c.v.3.c. for octahedrals, always have either 0, 1, or 2 lone pairs only c.v.4. XeF 4 c.v.4.a.
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 02/17/2012 for the course CHEM 105ALg taught by Professor Bau during the Spring '07 term at USC.

Page1 / 6

Ch 10 - Ch. 10: Chemical Bonding II: Molecular Shapes,...

This preview shows document pages 1 - 3. Sign up to view the full document.

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