1 / 15

Molecular Orbitals

Explore the molecular orbital model, electron distributions, and bond strengths in molecules like H2. Learn the differences between bonding and anti-bonding orbitals, electron probability distributions, and bond order calculations.

felipek
Download Presentation

Molecular Orbitals

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Molecular Orbitals Chapter 9

  2. Molecular Orbital model • This model examines unpaired electrons, bond energies and excited state electrons. • Examine the H2 molecule. • When 2 atomic orbitals overlap, two molecular orbitals form. • One low energy bonding orbital and one high energy anti-bonding orbital

  3. Electron Probability Distribution • The electron probability of both MO and MO* is centered along the line passing between the nuclei. • In the MO, the greatest e- probability is between the nuclei. • In MO* the greatest e- probability is on either side of the nuclei

  4. Describing the bonding • The molecular orbitals are constructed from the atomic 1s orbitals of the H atoms. • The resulting molecular orbital may be represented as : • MO1 = 1sa +1sb • MO* = 1sa – 1sb

  5. Important points • The e- probability is centered along the line passing between the two nuclei.. • This type of electron distribution is described as sigma (σ). MO1 & MO* are sigma molecular orbitals. • In this model only molecular orbitals are available for occupation by electrons. Atomic orbitals no longer exist because the molecule , a new entity, has its own set of new orbitals.

  6. Bonding & Anti-bonding

  7. More points • MO1 is lower in energy than 1s of the free H atom. • This is the driving force behind molecular formation, and stability. • If the electrons are forced to occupy the higher energy MO*, or anti-bonding orbitals, that reduces the stability of the molecule. • Bonding MO’s are lower energy than individual atomic orbitals. • Anti-bonding MO’s are higher energy than individual atomic orbitals.

  8. Last points • Molecular orbitals may be written like electron configurations. σ 1s2 etc. • Each molecular orbitals holds up to 2 electrons with opposite spin. • Orbitals are conserved. The number of molecular orbitals will always be the same as the number of atomic orbitals used to construct them.

  9. Examples

  10. Bond Order • Bond order is defined as bond order = ½ [(# of bonding e-) - (# of anti-bonding e-)]

  11. More examples • Oxygen has a bond order of 2, but it also shows two unpaired electrons. • ½(10-6)=2 • The larger the bond order, the greater the bond strength.

  12. Still other examples

  13. Try it • Which is stable, He2 or Li2? • With a bond order of 0 versus 1, Lithium is more stable. • Which is more stable, O2, O2+ or O2- ? • 2, 2.5 and 1.5 indicate that O2+ is the most stable.

  14. Paramagnetism • Unpaired electrons exhibit paramagnetism. • In this picture liquid oxygen is held in a magnetic field until it boils away.

More Related