6/25/2015 One Point Quiz  One quiz per table, list everyone’s name  Agree on an answer  You have two minutes

Molecular Orbital Theory Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

6/25/2015 Bonding Theories  Ionic Model  Skeleton Diagrams  Lewis Dot Diagrams Formal Charge, Resonance  Molecular Orbital Theory Extends atomic orbitals concepts to molecules

6/25/2015 Bonding in Diatomic Molecules B A+A+ Ionic bonding Diatomic: molecule contains two atoms large difference in electronegativity Covalent bonding D C small difference in electronegativity Give an example of a compound with ionic bonding.

6/25/2015 Homodiatomic Molecules The best example of covalent bonding involves homodiatomic molecules. Contains two of the same type of atom. e.g., H 2, O 2, F 2, N 2 WhyWhy are these molecules the best examples of covalent bonding? A A

6/25/2015 Homodiatomic Molecules The best example of covalent bonding involves homodiatomic molecules. Contains two of the same type of atom. e.g., H 2, O 2, F 2, N 2 Why are these molecules the best examples of covalent bonding? Bonding electrons are exactly shared because both atoms have the same electronegativity. A A

6/25/2015 Heterodiatomic Molecules H - F positive endnegative end HF, BN and CO are heterodiatomic molecules. Contain two different atoms. These molecules are polar covalent. What factors might help predict the positive and negative ends of the molecule?

A Little Review What is an orbital? What is the maximum number of electrons that can be in one orbital? What is the name of the mathematical function that determines the shape of an orbital? Give an example of an atomic orbital?

6/25/2015 Molecular Orbitals When two atoms come close to each other, what happens to the orbitals of each atom? a bond forms 1s atomic orbital 1s atomic orbital  s b molecular orbital sigma s bonding molecular orbital

6/25/2015 Molecular Orbitals Orbital wave functions can add & subtract to give new wave functions and corresponding molecular orbitals (mo). Atoms bond together when the wave functions constructively overlap.

6/25/2015 SIGMA BOND (  ) A bond between two atoms in which the electron density of the molecular orbital is between the two nuclei is called a sigma bond. (  s b ) 2 molecular orbital nuclei

6/25/2015 Molecular Orbitals (mo)  Obey many of the same rules as atomic orbitals (ao). two electrons per molecular orbital. specific regions of space. one molecular orbital formed for each atomic orbital used.

6/25/2015 Wave Functions The amplitude (height) of each wavefunction can either be positive or negative.

6/25/2015 Wavefunctions Bonding & Antibonding Orbitals bb Constructively interfere in certain regions of space. ** Destructively interfere in certain regions of space.

6/25/2015 Bonding & Antibonding Orbitals HH sbsb s*s* When a bonding molecular orbital forms, an antibonding molecular orbital also forms. Bonds form where orbitals overlap and electrons are.

6/25/2015 Atomic and Molecular Orbitals x y z 1s 2p y 3d z 2 Atomic orbitals include

6/25/2015 Atomic and Molecular Orbitals sbsb z z*z* x*x* x y Molecular orbitals include

6/25/2015 Atomic and Molecular Orbitals This represents an orbital

6/25/2015 Atomic and Molecular Orbitals energy An orbital can be empty or can contain 1 or 2 electrons. Orbitals can have different energies carbon: 1s 2 2s 2 2p 2

6/25/2015 Molecular Orbital Diagrams  Examples dihydrogen dihelium dihelium(I) ion dilithium dilithium(I) ion dilithate ion

6/25/2015 Dihydrogen, H 2 1s 1 hydrogen orbital of two hydrogen atoms Two 1s 1 hydrogen orbitals overlap to form a  s b bonding molecular orbital HH sbsb energy s*s* The branch lines indicate which atomic orbitals are involved in generating the molecular orbitals. HH

6/25/2015 moao Dihydrogen, H 2 sbsb energy s*s* Dihydrogen is diamagnetic and contains one bond (one pair of bonding electrons). HH What advantage can an orbital gain in forming a molecular orbital from an atomic orbital? electronic configuration of the hydrogen molecule. (sb)2(sb)2 Why is dihydrogen diamagnetic?

6/25/2015 Each helium atom has the electronic configuration 1s 2 (each contributes 2 electrons to the helium molecular orbitals) Dihelium, He 2 energy atomic orbital of one He atom atomic orbital of the other He atom sbsb s*s* Two electrons occupy the highest molecular orbital forming a  s * Two electrons occupy the lowest molecular orbital forming a  s b

6/25/2015 Dihelium, He 2 The electronic configuration of the dihelium molecule is (  s b ) 2 (  s *) 2 energy sbsb s*s* WhyWhy doesn’t He 2 exist as a stable molecule?

6/25/2015 Dihelium, He 2 The electronic configuration of the dihelium molecule is (  s b ) 2 (  s *) 2 energy sbsb s*s* Why doesn’t He 2 exist as a stable molecule? Antibonding implies there is a “negative” bond 1 bond + 1 antibond = zero net bonds

6/25/2015 Dihelium(I) Ion, He 2 + energy How many valence electrons must be considered in the dihelium(I) ion? He He + Complete the molecular orbital diagram using the available electrons. sbsb s*s* He

6/25/2015 Dihelium(I) Ion, He 2 + energy Lined means 1 He He + These represent the atomic orbitals. Shaded means 2 electrons sbsb s*s*

6/25/2015 Dihelium(I) Ion, He 2 + energy Draw an outline of the molecular orbitals. Fill-in Fill-in the molecular orbitals, shaded for 2 electrons, lined for 1. He He + sbsb s*s*

6/25/2015 Dihelium(I) Ion, He 2 + The sigma bonding orbital contains two electrons, the sigma antibonding orbital contains one electron. What is the electronic configuration of the dihelium(I) ion? (  s b ) 2 (  s *) 1 energy sbsb s*s*

6/25/2015 What physical properties are predicted for the dihelium(I) ion? energy sbsb s*s* (magnetic and bond order) Dihelium(I) Ion, He 2 +

6/25/2015 Dihelium(I) Ion, He 2 + What physical properties are predicted for the dihelium(I) ion? energy sbsb s*s* Dihelium(I) ion is paramagnetic (one unpaired electron) and has a bond order of 1/2. (magnetic and bond order)

Dilithium Molecule “Beam me up, Scotty” “I can’t sir, it’s …the dilithium crystals …”

6/25/2015 Dilithium Molecule, Li 2  Each lithium atom has the electronic configuration 1s 2 2s 1. The 2s orbitals of the lithium atoms overlap well.

6/25/2015 Dilithium Molecule, Li 2  The 1s orbitals are much smaller (r  n 2 ) and do not overlap well. These orbitals do not substantially contribute to the bonding in this molecule.

6/25/2015 Dilithium, Li 2 energy 2s 1s There is no gain in stability or lowering of energy. These are nonbonding orbitals (  1s n )

6/25/2015 Dilithium, Li 2 energy The 2s orbitals constructively overlap and form a sigma bonding molecular orbital (  s b ). 2s 1s sbsb

6/25/2015 Dilithium, Li 2 energy The 2s orbitals destructively overlap and form a sigma antibonding molecular orbital (  s *). 2s 1s s*s*

6/25/2015 Dilithium, Li 2 energy (  s n ) 4 (  s b ) 2 or (  s b ) 2 2s 1s (sn)4(sn)4 Often the inner shell nonbonding electrons are not listed for the molecular orbital. Generally, only outer shell (valence) electrons are involved in bonding. (sb)2(sb)2

6/25/2015 Dilithium, Li 2 energy What physical propertiesphysical properties are predicted for dilithium?

6/25/2015 Dilithium, Li 2 energy What physical properties are predicted for dilithium? diamagnetic bond order of one

6/25/2015 Dilithium(I) Ion, Li 2 + energy one valence electron 2s 1s Only orbitals which overlap are considered electronic configuration sbsb (sb)1(sb)1 bond order? 1/2 magnetic property? one unpaired electron paramagnetic

6/25/2015 Dilithium(I) Ion, Li 2 + energy 2s sbsb atomic orbitals overlap molecular orbitals

6/25/2015 s*s* sbsb 2s LiLi 2 – Li – 1s Dilithate Ion, Li 2 – energy (sb)2 (s*)1(sb)2 (s*)1 magnetic property? 1 unpaired electron paramagnetic bonding electronic configuration? bond order? 4 nonbonding e – 2 bonding e – 1 antibonding e – bond order 0.5

6/25/2015 Dilithate Ion, Li 2 –  Draw the molecular orbitals involved in bonding. Shaded orbital for two electrons. Lined orbital for one electron. Open orbital for no electrons.

6/25/2015 Dilithate Ion, Li 2 – (sb)2 (s*)1(sb)2 (s*)1

6/25/2015 Compare and Contrast How would the bond lengths of the various dilithium species be expected to vary? dilithium, Li 2 dilithium(I) ion, Li 2 + dilithate ion, Li 2 –  bond order 1  bond order 0.5 Li 2 < Li 2 +  Li 2 –

Lithium Hydride What would the orbital overlap and molecular orbital diagram look like for lithium hydride?

6/25/2015

Unknown Dues Dates  Unknown AFriday, Week 5  Unknown BFriday, Week 7  Unknown CFriday, Week 9  Unknown DFriday, Week 10

6/25/2015 Extra Period Laboratory Monday, April 27 1:35 - 4:15 pm Especially For Those Who Cannot Attend Any Other Extra Period No Sign Up Needed First Come Basis