Electronic Structure of an atom refers to the number and distribution of electrons around the nucleus.

Wave-Particle Nature of Light

Quotation: "Anyone who is not shocked by quantum theory has not understood it."

-Niels Bohr

The Delayed Choice Experiment (Scientific American Jan. 1988, p. 46)

Experimental setup.

Procedure:

1. The laser is fired and one photon is sent into the beam splitter.

2. If the photon behaves like a particle it will take either path A or A' as it leaves the beam splitter.

3. If the photon behaves like a wave it will "split" in two and take both paths and interfere with itself.

4. After the photon leaves the beam splitter the switch is triggered.

5. If the switch is turned to the "on" position the photon either takes path A or path A' and is detected by the photodetector. It behaves as a particle with a definite path.

6. If the switch is turned to the "off" position the photon takes both paths and produces an interference pattern. It behaves as a wave.

How does the photon decide how to behave?

Possible Explanations

1. The photon knows how the switch will be turned in advance and makes a decision before leaving the beam splitter.

(New Age)

2. The nature of the photon is indeterminate until the switch is turned and an observation is made: the photon becomes a wave or becomes a particle.

The observation makes the photon a wave or a particle.

(accepted by Bohr and most physists)

(Is reality objective? Do we create reality by observations?)

3. God controls both the "decision" of the photon and the experimenter.

Thought experiment with quasar.

DeBroglie (1924) proposed that matter has ____________ properties.

l = h/(mv) = wavelength associated with a particle

The smaller the particle, the smaller m is, the greater l is, and the more important wave properties are.

Evidence for Wave Properties of Matter

Davisson and Germer (1927): Showed that electrons can be diffracted by a nickel crystal. This indicates that _____________________

Wave Mechanical Model of the Atom

Schrodinger (1926)

Assumption: Electrons in an atom behave as _______________.

Guitar string analogy

(transparency/chalkboard)

Only certain wavelengths are possible for standing waves.

Schrodinger Wave Equation

HY = EY (analogous to eq. for mechanical waves)

H is an operator.

E is the energy of the electron.

Y is the wave function of the electron and describes the properties of the electron.

Hydrogen atom

solutions: Y₁, Y₂, Y₃, ..., Y_n

1. Only certain 3-d "waveforms" possible for the electron in H atom.

2. Each "waveform" is called an orbital and describes the possible energy states of the electron. It also tells us where the electron can usually be found when in a given energy state. (orbitals have _________________________)

Y²(x,y,z) a electron density at (x,y,z)

3. Each orbital can be specified by 3 quantum numbers which describe the various properties of the orbital.

n, principal quantum number:__________________________________

n = 1, 2, 3,..., 7

l, orbital angular momentum quantum no.:_______________________________

l = 0, 1, 2,..., n - 1

l........designation of orbital

0.......s

1.......p

2.......d

3.......f

s orbital:

p orbital:

d_xy:

d_z2:

Sign of wave function does not affect electron density.

Sign of wave function is important for _____________________

m_l, magnetic quantum number: ________________________________

m_l = -l, -l + 1, ..., 0, ...,l - 1, l

There are 2l + l orbitals with quantum number l, each with a different orientation.

n, l, & m_l determine the orbital.

m_s, spin quantum number: within an orbital the electron can have one of two possible "spins" corresponding to m_s = +1/2 or -1/2

(table of orbitals)