12a - The chemical bond Why do some combinations of atoms...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon
1 The chemical bond •Why do some combinations of atoms form stable molecules? •Why other combinations of atoms do not form stable molecules? •What determines the bond strength? •What determines the molecular geometry? •What determines if a chemical reaction will take place? •What determines the properties of molecules (optical, electrical, magnetic, etc). Lewis model, Octet rule, VSEPR (Valence Shell Electron Pair Repulsion) Quantum Chemistry Fundamental, Quantitative, Demanding (But – commercial software packages are available and commonly used nowadays) Phenomenological, Qualitative, Easy to apply
Background image of page 1

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

View Full DocumentRight Arrow Icon
2 The electrons are much lighter than the nuclei: 1836 1. The electrons move much faster than the nuclei! p e m m = ± The Born-Oppenheimer approximation (1927) 1. Solve the for different frozen configuraions of the nuclei. 2. Electronic Schrodinger equation electronic potential surfac "Connect-the-dot" to form . 3. Sol es Nuclear Schrodinger eq ve the uation for each of the electronic surfaces. 4. The corresponds to the Minimum of the electronic po molecular geometry tential surface. Strategy E(R) R R eq R
Background image of page 2
3 + 2 The H molecule The molecular orbitals (MO's) at R= . eq R E n e r g y g "Gerade" (Symmetrical with respect to inversion through Angular momentum component along bond axis = the center of the molecule): 1 1s The atomic Ground s (- ,- ,- ) ( tat , e , or . 0. ). g xyz s σ ψψ = 2 + R ++ no "*" Bonding: energy lower than H(1s)+H , bital in the dissociated molecule (when R ): high electronic density in H ( 1 ) the region H(1s)+H . between nuclei, well g s →∞ →∞ ⎯⎯⎯→ -shaped potential. * u "Ungerade" (anti-symmetrical with respect to in Angular momentum com version through First excited the center ponent alon of the mole state cule): g bon (- 1 1 d axis = 0. ,- ,- ) ( , , :. s u s ψ =− + + + * R 2 * Anti-bonding The atomic orbital i : energy higher than n the dissociated molecule (when R ): H(1s)+H , low electronic den H ( 1 ) si H(1s)+H . ty in the region between nucle u s →∞ ⎯⎯→ i, repulsive potential surface.
Background image of page 3

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

View Full DocumentRight Arrow Icon
4 g "Gerade" (Symmetrical with respect to inversion thro Angular momentum component ugh the center of 2 2s The ato the mo along lecul 2-nd excited e): (- ,- bond axis = , s - tate .
Background image of page 4
Image of page 5
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 06/13/2009 for the course CHEM 260 taught by Professor Staff during the Spring '08 term at University of Michigan.

Page1 / 10

12a - The chemical bond Why do some combinations of atoms...

This preview shows document pages 1 - 5. Sign up to view the full document.

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