Orbitals

1. Orbitals … and more orbitals

2. When atoms are close together… • Atomic orbitals on each atom are affected by the presence of other atoms. • Attraction of the other nuclei for the electrons in an atom pulls them into different volumes of space than they would be in, if the atom were isolated. • All atoms experience these changes. • We call this hybridization.

3. Let’s consider Carbon, without Hybridization • According to our energy level diagram, an isolated carbon atom has a full s, and two singlets in p orbitals, with one p orbital completely empty.

4. This means that only two covalent bonds can form: the singlets being attracted toward another nucleus, and an electron from that atom attracted toward the carbon.

5. The s orbital stays unshared. The two electrons in it repel all other electrons.

6. And, the last p stays empty UNLESS another atom (with an unshared pair) shares its own two electrons with carbon.

7. That’s not what happens • Carbon will pull an electron from another atom into the empty orbital • And that other atom will pull one of carbon’s paired electrons into that orbital. • Another electron will be pulled into the remaining orbital.

8. Hybridization • All of this pushing and pulling changes the orbitals. • The four valence atomic orbitals hybridize into new orbitals. • These orbitals are not s orbitals, not p orbitals, but something in-between. • These are the most stable orbitals when there are additional atoms nearby.

9. Atomic orbitals hybridize • The new orbitals are equivalent, and of equal energy. • The four electrons split. • Carbon bonds to four separate atoms, forming four single ( bonds.

10. 4 hybrid orbitals form • They all have the same energy and the same shape. They are fully equivalent. • Each of these orbitals has 1/4 s character and 3/4 p character. • Their energies are in-between those of the original s & p orbitals. • Their shapes are in-between those of the original s & p orbitals.

11. How to Visualize hybrid orbitals • They look like funny little lopsided p orbitals. • They point in 4 different directions, due to the repulsion between electron pairs. • They are called sp3 orbitals (from sppp) http://ww2.educarchile.cl/UserFiles/P0001/Image/Mod_2_contenidos_estudaintes_ciencias_quimica/Quimica_cambio_6.jpg

12. sp3 Hybrid orbitals • How do the orbitals fit together? • Tetrahedral arrangement http://wps.prenhall.com/wps/media/objects/724/741576/Instructor_Resources/Chapter_01/Text_Images/FG01_12.JPG

13. What about double & triple Bonds? • π bonds form from the overlap of perfectly parallel pure p orbitals. • Hybrid orbitals are not pure p orbitals • Hybrid orbitals do not form π bonds.

14. Double Bonds • One  bond and one π bond. •  bond forms when any two orbitals (including hybrid orbitals) overlap straight-on. • π bond only forms from pure p orbitals. • Atom hybridizes only 3 orbitals, not all 4. • The original s and two of the original p orbitals hybridize to form 3 identical orbitals.

15. 3 hybrid orbitals form • They all have the same energy and the same shape. They are fully equivalent. • Each of these orbitals has 1/3 s character and 2/3 p character. • Their energies are in-between those of the original s & p orbitals. • Their shapes are in-between those of the original s & p orbitals.

16. More hybrid orbitals to visualize • They still look like funny little lopsided p orbitals. • They point in 3 different directions, due to the repulsion between electron pairs. • They are called sp2 orbitals (from spp) • The remaining p orbital forms the π bond. Top view of 3 sp2 orbitals http://image.tutorvista.com/content/organic-chemistry/sp2-hybridization-carbon-orbital.gif

17. sp2 Hybrid orbitals • How do the orbitals fit together? • Trigonal planar arrangement

18. Triple Bonds • One  bond and two π bonds. •  bond forms when any two orbitals (including hybrid orbitals) overlap straight-on. • π bonds only form from pure p orbitals. • Atom hybridizes only 2 orbitals, not 3 or 4. • The original s and one of the original p orbitals hybridize to form 2 identical orbitals.

19. 2 hybrid orbitals form • They have the same energy and the same shape. They are fully equivalent. • Each of these orbitals has 1/2 s character and 1/2 p character. • Their energies are in-between those of the original s & p orbitals. • Their shapes are in-between those of the original s & p orbitals.

20. Still more hybrid orbitals to visualize • They still look like funny little lopsided p orbitals, but more s-like than the others. • They point in 2 different directions, due to the repulsion between electron pairs. • They are called sp orbitals • The remaining two p orbitals form 2 π bonds. sp orbitals formed from s & p orbitals http://www.cartage.org.lb/en/themes/Sciences/Physics/MolecularPhysics/ElectronicStructure/ChemicalBond/Moleculargeometry/fig6-17.jpg

21. sp Hybrid orbitals • How do the orbitals fit together? • Linear arrangement

22. Summary • When making only  bonds: atoms use sp3 hybridization • When making one π bond: atoms use sp2 hybridization • When making two π bonds: Atoms use sp hybridization