Molecular orbital theory

Chemical Engineering Organic&Inorganic chemistry lecture

1. Molecular Orbital Theory BY Zameer Ahmed18CH19 QUEST NAWABSHAH

2. Referances of our presentation Knowbee Mastering Organic chemistry. Parveen Jhambre . O&I Cemistry of SINDH and PUNJAB Board. Professor Davi Explains. Lectures of Sir Mehmmod Nabi Abbasi .

3. Some websites http ://www.chemguide.co.uk/atoms/properties/atomorbs.html http://www.ch.ic.ac.uk/vchemlib/course/mo_theory/main.html http://en.wikipedia.org/wiki/Molecular_orbital_theory http://library.thinkquest.org/27819/ch2_2.shtml

4. Aslam0Alaikum to my respectable teacher and my class fellows and GOOD MORNING. Today My presentation on topic “MOT”. First off all, I want to tell you about defination,procedure and structure of MOT of some molecules .

5. In 1927 hietler and london proposed the valance Bond theory .Valence Bond Theory fails to answer certain questions like Why He 2  molecule does not exist and why O 2  is paramagnetic? Therefore in 1932 F. Hood and Robert S . Mulliken came up with theory known as  Molecular Orbital Theory  to explain questions like above. According to Molecular Orbital Theory individual atomic orbitals combine to form molecular orbitals, as the electrons of an atom are present in various atomic orbitals and are associated with several nuclei.

6. MOT means molecular orbital theory When two atoms are combine to form a molecule then Each atoms of atomic orbital combine to form molecular orbital, Molecular orbitals are classified on the basis of energy, 1) Bonding Orbital 2) Anti Bonding Orbital The orbital having lowest energy is called Bonding Orbital, The orbital having high energy is called AntiBonding orbital

7. When addition of wave function takes place, the type of molecular orbitals formed are called Bonding Molecular orbitals and is represented by  Ψ MO  = Ψ A  + Ψ B . They have lower energy than atomic orbitals involved. It is similar to  constructive interference occurring in phase because of which electron probability density increases resulting in formation of bonding orbital.

8. Anti-Bonding Molecular Orbitals When molecular orbital is formed by subtraction of wave function, the type of molecular orbitals formed are called  Antibonding Molecular Orbitals  and is represented by Ψ MO   = Ψ A  - Ψ B . They have higher energy than atomic orbitals. It is similar to  destructive interference  occurring out of phase resulting in formation of antibonding orbitals. Molecular Orbital formed by subtraction of overlapping of two s orbitals.  

9. It is represented by s* (*) is used to represent antibonding molecular orbital) called Sigma Antibonding . Combination of two atomic orbitals results in formation of two molecular orbitals, bonding molecular orbital (BMO) whereas other is anti-bonding molecular orbital (ABMO). BMO has lower energy and hence greater stability than ABMO . First BMO are filled then ABMO  starts filling because BMO has lower energy than that of ABMO.

10. Rules for Filling of Molecular Orbitals Certain rules are to be followed while filling up molecular orbitals with electrons in order to write correct molecular configurations: Aufbau Principle  – This principle states that those molecular orbital which have the lowest energy are filled first. Pauli’s Exclusion Principle  – According to this principle each molecular orbital can accommodate maximum of two electrons having opposite spins. Hund’s Rule  – This rule states that in two molecular orbitals of the same energy, the pairing of electrons will occur when each orbital of same energy consist one electron

11. Bond Order It may be defined as the half of difference between the number of electrons present in the bonding orbitals and the antibonding orbitals  that is, Bond order (B.O.) = (No. of electrons in BMO - No. of electrons in ABMO)/ 2. Those with positive bonding order are considered stable molecule while those with negative bond order or zero bond order are unstable molecule .

12. Magnetic Behavior : If all the molecular orbitals in species are spin paired, the substance is diamagneti . But if one or more molecular orbitals are singly occupied it is paramagnetic .  For Example , if we look at  CO Molecule ,  it is diamagnetic  as all the electron in CO are paired.

13. When we discuss about MOT of hydrogen molecule then we know that in valance shell of hydrogen atom have one one electron, When they combine together they form sigma bond. There is no any electrons are in Antibonding molecular orbital. Both two electrons are occupy bonding molecular orbital. Hydrogen molecule is formed sigma bond by combination of S-S orbital

14. MOT of Hydrogen H2 1S 1 1S 1

15. Mot of oxygen molecule

16. Mot of carbon mono oxide

17. MOT OF NITRICOXIDE