Shapes of Molecules, Valence Bond Theory, Hybridization, MO Theory, IMF

Chem 110

Why do we care about molecular geometry?

molecular polarity/dipole moments, IMFs, binding, and reactivity

VSEPR

Valence Shell Electron Pair Repulsion Theory: maximize the space between valence ELECTRON GROUPS around an atom

What can be considered an electron group?

ONE electron can be a: lone pair, single bond, double/triple bond, or a single unpaired electron

How do electrons arrange themselves?

electron groups arrange themselves to minimize repulsion from the regions of concentrated negative charges

What are the steps for VSEPR

1. write the lewis structure

2. count the # of regions of electron density around central atom

3. identify geometry based on # of regions of electron density

4. use the number of lone pairs to determine molecular structure

Molecule AX₂

Linear Geometry: 2 EG = 2 BG + 0 LP

Bond Angle XAX: 180

Molecule AX₃

Trigonal Planar: 3 EG= 3 BG + 0 LP

Bond Angle XAX: 120

Molecule AX₂E

Bent: 3 EG= 2 BG + 1 LP

Bond Angle XAX: <120

wedge

the nucleus/electron is coming out of the page

dash

the nucleus/electron is going into the page

Molecule AX₄

tetrahedral: 4 EG = 4 BG + 0 LP

Bond Angle XAX: 109.5

molecule AX₃E

trigonal pyramidal: 4 EG — 3 BG + 1

Bond Angle XAX: <109.5

molecule AX₂E₂

bent: 4 EG = 2 BG + 2 LP

bond angle XAX: < 109.5

moleculeAX₅

trigonal bipyramidal: 5 EG = 5 BG + 0 LP

Bond Angles XAX: Axial = 90 and Equatorial = 120

molecule AX₄E

see-saw: 5 EG = 4 BG + 1 LP

Bond Angles XAX: <120 and <90

molecule AX₃E₂

t-shaped: 5 EG = 3 BG + 2 LP

bond angle XAX: < 90

molecule AX₂E₃

linear: 5 EG = 2 BG + 3 LP

bond angle XAX: 180

molecule AX₆

octahedral: 6 EG = 6 BG + 0 LP

molecule AX₅E

square pyramidal: 6 EG = 5 BG + 1 LP

bond angle XAX: < 90

molecule AX₄E₂

sqaure planar: 6 EG = 4 BG + 2 LP

bond angles XAX: 90

what is the polar range for polar covalent bonds?

0.5 - 1.9

sigma bond

the bond formed from the overlap of two orbitals that is cylindrically symmetrical around the bond axis

pi bond

the bond formed from the overlap of two orbitals that is not symmetrical around the bond axis

What is a limitation of valence bond theory?

valence bond theory cannot predict the geometry for all molecules