Answers: Molecular Orbital Theory
- A molecular orbital is a Schrodinger's orbital which can include several but usually only 2 nuclei.
- An orbital is the region where there is a 95% probability of locating an electron in a free atom.
- There are mainly 4 types of orbitals (s,p,d and f) and each orbital can hold a maximum of 2 electrons.
- State the 3 main rules in this theory
1. The molecular orbitals are filled in a way that yields the lowest potential energy for the molecule. In other words the electrons must fill up 1s before 2s and 2s before 2p.
2. Each orbital can only contain 2 electrons
3. Orbitals of equal energy are half filled with parallel spin before they begin to pair up which means that electrons are half-filled(the arrow pointing up) before they can pair up with the other electron(the arrow pointing down). ------------------------------------------------------------------------------------------------
- A bonding order is basically the number of bonds formed
- The bonding order tells us the stability of the molecule and whether it is diamagnetic or paramagnetic.
- Diamagnetic basically means that all of the electrons that are being shared forms a pair and is basically stable.
- Paramagnetic means that one or more electrons is unpaired and the molecule is unstable.
- bonding order of molecules is calculated by :
1/2(number of bonding molecular orbitals - number of anti-bonding molecular orbitals)
· Draw the molecular orbital diagram of H2.
The bond order is 1/2(2 - 0) = 1
· Draw the molecular orbital diagram of O2
The bond order is 1/2(10 - 6) = 2
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- Where the atomic orbitals overlap, the in-phase interaction leads to an increase in the intensity of the negative charge in the region where they overlap.
- This creates an increase in negative charge between the nuclei and an increase in the attraction between the electron and the nuclei for the atoms.
- The greater attraction leads to lower potential energy and because electrons in the molecular orbital are of lower potential energy than in separate atomic orbitals, energy would be required to shift the electrons back into the 1s orbitals of separate atoms.
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- Where the atomic orbitals overlap, the out-phase interaction leads to a decrease in the intensity of the negative charge.
- This creates a decrease in negative charge between the nuclei and a decrease in the attraction between the electron charge and the nuclei for the atoms in the bond.
- The lesser attraction leads to lower potential energy and the electrons are more stable in the 1s atomic orbital of separate atoms, so electrons in this type of molecular orbital destabilizes the bond between atoms.
Answers: MCQ
Q1) 4
Q2) 2
Q3) 2
Q4) 1
Q5) 3
