Exercise III: Molecular Orbital Theory
* Valence bond theory would predict all electrons are paired with opposite spins; and hence all molecules should not have unpaired spins. However, O2 molecule at ground state has unpaired spin; it is a paramagnetic molecule.
* One needs a better theory to understand the bonding in molecule. Hence the development of molecular orbital theory
* We will only study the molecular orbital theory applied to treat the diatomic molecules. Important concepts you need to grasp on is the âmolecular orbitalsâ, bonding and antibonding; and bond order of the formed molecules.
1. (a) Take two H atoms; each has 1s atomic orbital; Sketch to show how the two 1s atomic orbitals form bonding and antibonding molecular orbitals.
(b) In H2 molecule, how many valence electrons it has? Which molecular orbitals these electrons would go? What is the final resulting âbond orderâ in this molecule.
(c) Take He2, how many valence electrons this molecule has in total?Which molecular orbitals these electrons would occupy? What is the final bond order you find for this molecule?
(d) What would be bond order you will find for He2+ ion?
2 (a) Consider F2 molecule. How many valence electrons F atom has? What atomic orbitals they are in?
(b ) Sketch to draw formation of molecular orbitals that could be formed using 2s and 2p atomic orbitals. Make sure you show the relative energies of these formed molecular orbitals and write their names and labels correctly.
(c ) Place all valence electrons in F2 molecule in these molecular orbitals. Calculate the bond order you find for F2 molecules. Does the molecule contain any unpaired electrons?
(d) Write the molecular orbital configuration for F2 molecule (molecular orbital configuration is similar to electron configuration for atom, except you will show how many electrons are found in each molecular orbitals).
(e) Do the same for O2 molecule. What is the bond order you find? Does it contain any unpaired electrons?
(f ) Write the molecular orbital configuration for O2 molecule.
(g) For N2 molecule, the relative order of molecular orbitals differs from that applicable to O2 molecule. Sketch to show how the molecular orbitals are arranged for N2 molecules.
(h) Use the above correct order, write molecular orbital diagram for N2 molecule; calculate the bond order and indicate the molecule is diamagnetic or paramagnetic.
(i) Do that for N2- ion; again and calculate the bond order and indicate if it is diamagnetic or paramagnetic.
Exercise III: Molecular Orbital Theory
* Valence bond theory would predict all electrons are paired with opposite spins; and hence all molecules should not have unpaired spins. However, O2 molecule at ground state has unpaired spin; it is a paramagnetic molecule.
* One needs a better theory to understand the bonding in molecule. Hence the development of molecular orbital theory
* We will only study the molecular orbital theory applied to treat the diatomic molecules. Important concepts you need to grasp on is the âmolecular orbitalsâ, bonding and antibonding; and bond order of the formed molecules.
1. (a) Take two H atoms; each has 1s atomic orbital; Sketch to show how the two 1s atomic orbitals form bonding and antibonding molecular orbitals.
(b) In H2 molecule, how many valence electrons it has? Which molecular orbitals these electrons would go? What is the final resulting âbond orderâ in this molecule.
(c) Take He2, how many valence electrons this molecule has in total?Which molecular orbitals these electrons would occupy? What is the final bond order you find for this molecule?
(d) What would be bond order you will find for He2+ ion?
2 (a) Consider F2 molecule. How many valence electrons F atom has? What atomic orbitals they are in?
(b ) Sketch to draw formation of molecular orbitals that could be formed using 2s and 2p atomic orbitals. Make sure you show the relative energies of these formed molecular orbitals and write their names and labels correctly.
(c ) Place all valence electrons in F2 molecule in these molecular orbitals. Calculate the bond order you find for F2 molecules. Does the molecule contain any unpaired electrons?
(d) Write the molecular orbital configuration for F2 molecule (molecular orbital configuration is similar to electron configuration for atom, except you will show how many electrons are found in each molecular orbitals).
(e) Do the same for O2 molecule. What is the bond order you find? Does it contain any unpaired electrons?
(f ) Write the molecular orbital configuration for O2 molecule.
(g) For N2 molecule, the relative order of molecular orbitals differs from that applicable to O2 molecule. Sketch to show how the molecular orbitals are arranged for N2 molecules.
(h) Use the above correct order, write molecular orbital diagram for N2 molecule; calculate the bond order and indicate the molecule is diamagnetic or paramagnetic.
(i) Do that for N2- ion; again and calculate the bond order and indicate if it is diamagnetic or paramagnetic.
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