Quantum Mechanics 2
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When atoms combine to form molecules:
They attempt to achieve the lowest energy level
In covalent binding:
Two single atomic orbitals combine to become a molecular orbital
S-s-sigma bonding
When two s orbitals combine to create a. Ew orbital that contains both electrons
p-p-sigma Bonding
Crates a lower energy orbital energy than the single p orbital as well as a higher energy sigma orbital; occurs when two p orbitals overlap; plus and minus wavefunction only combine with the like signs
s-p-sigma bonding
When s and p orbitals combine; s can only have a positive wave function to combine with the positive part of the p orbital
p-p-pi bonding
Not rotation symmetric: but symmetric about a plane; when two of the orbitals like pz and py approach each other along the x axis
There are a maximum of three covalent bonds that are allowed between two atoms:
One p-p-sigma bonds (px-px-sigma) Two p-p-pi bonds (py-py-pi;pz-pz-pi)
Bond order
Bond order = (# of e- in bonding MO- # of e- in antibonding MO)/2
Molecules with paired electrons are:
Diamagnetic and do not interact with a magnetic field
Molecules with unpaired electrons are:
Paramagnetic and interact with a magnetic field
Two properties of electromagnetic radiation
Amplitude Periodicity They are described by wavelength, wave number, and frequency
Frequency (v)
Number of waves that pass a given point in time; v = c/wavelength; c = 3.0x10^8 m/s
Wavelength
The distance from crest to crest on adjacent waves
Wave number
The number of waves per unit distance, so it has the units reciprocal to distance cm^-1 Wave number = 1/wavelength
Energy of a photon
Ep = hv
Amount of energy absorbed or emitted by a molecules
dEm = Ep = hv
Adsorption
If Em is positive, the photon is absorbed by the molecule
Emission
If Em is negative, the photon is emitted by the molecule
Doppler effect
An o next approaching an observer with speed v, while emitting radiation of wavelength y, seems to be emitting from [1-(v/c)]y rather than from y
Zeeman effect
The presence of a magnetic field will shift the energy levels between which transition occurs
Stark effect
An electrical field can shift spectral bands