Download Light and Electrons!

Light and Electrons!
Shining “light” on light, electrons, and their
properties
Andy Berger
5/30/08
Periods 1 & 2
René Descartes
Historical Theories
Two major societies contributing to Light theory
Isaac Newton
Indians: (5th-6th Cent. BC)
• First theories about light made by Hindu schools of Samkhya and
Vaisheshika
• Believed that light was one of the five fundamental subtle “elements” of
nature
• Developed from Indian atomism
• Believed that rays of light from sun were fire atoms at high speed
Greeks: (5th-2nd Cent. BC)
-Empedocles concluded that the Earth is made of four elements: earth, air, fire,
and water
-Euclid hypothesized that a beam of light projects from the eye
-Also had theories about the refraction of light
Others:
-René Descartes (first one to assume light acted in waves)
-forerunner of light theory; believed light to be a disturbance of the plenum
Historical Theories (cont’d)
-Isaac Newton: proposed that light came from one source and emanated in all
directions as particles
-Robert Hooke: came up with Law of Elasticity
-All were equally important in their contributions to the understanding of light
Lots of Light!!!
Robert Hooke
The Basics
•
What is light?
Definition: Light is electromagnetic radiation, that is, a self-propagated wave, or
particle, depending on the viewpoint, with several properties that is
sometimes seen by the human eye depending on the wavelength.
Properties of light waves:
1. Amplitude
2. Wavelength(λ)-measured in nm
3. Frequency(υ)-measured in Hz
Wavelengths of Light
Types of light:
1.Radio Waves
2. Microwaves
3. Infrared Waves
4. Visible Light
5. Ultraviolet Light
6. X-Rays
7. Gamma Rays
Classical Mechanics vs. Quantum
Mechanics
Classical Mechanics
Quantum Mechanics
-Newtonian Mechanics
-Theoretical, not entirely proven
-Objects that can be seen
-Objects can not be seen
-Traveling at “ordinary” velocities
-Traveling near the speed of light
-Realistic
-have measurable wave-like properties
-The basis of physics
Light? Wave or Particle
-Big dispute about whether light acts in waved or particles
-Main contenders Einstein and Max Planck; Einstein for particles, Planck for
waves
-Both developed equations:
Einstein- E = MC2
Planck- h = E/υ
E = energy M = Mass C = Speed of light
h = Planck’s Constant E = energy
υ = frequency
-Some claimed that light had to be particles because there was evidence of it
going around objects; also Photoelectric Effect by Einstein helped the cause
-Photoelectric Effect theorized that light has photons, or “packets” of energy
-A man named Thomas Young proved, however, that light acts in waves
because of his diffraction experiment in 1800
-Later, Louis de Broglie united the both theories
Duality of Nature
1924- Louis de Broglie brought together the ideas of wave and particle
properties of light
-Came up with the equation: λ = h/mv
-Duality of Nature/Light
-The smaller the object, the more obvious the waves (i.e. electrons)
-Basically, every object has its own wavelength and emits energy while
traveling
Heisenberg’s Uncertainty Principle – impossible to know the exact momentum
and location of an electron in space simultaneously
De Broglie
Radial Probability
-Schrödinger comes up with a way to find probability of finding an electron in
space
-Said that electrons moved “in a blur”
-Potential energy increases as electrons move out to farther energy
-Made an equation:
Prob. Of position
Prob. Of
momentum
-Theorized that 90% of all electrons could be found within a line near the third
electron shell
-Believed that nodes got smaller and Smaller as
electrons moved farther away from nucleus
Schrödinger’s Quantum Numbers
-Four in total:
1st Quantum Number=n
-describes size of electron cloud; has values 1…infinity
2nd Quantum Number=l
-describes shape of electron region; has values 0…n-1, but depends on n
3rd Quantum Number=m
-tells the orientation in space; values depend on l, m=(-l…0…+l)
4th Quantum Number=s
-describes the spin; is either +1/2(clockwise) or -1/2(counter-clockwise)
Total Number of Electrons in a shell = 2n2
-Potential energy increases as electrons move out to farther energy
Bohr’s Model
-Each orbital has a
specific energy, and
each electron is in a
distinct energy region
Nodes-space in
between shells
-Works only for a 1
electron system
Lowest
orbital
Equation for “electron jumping”: E = (-2.18 x 10-18)(final 1/n2 – initial 1/n2)
Electron Configurations
-Idea here is showing the electrons for each shell using three rules:
Aufbau Principle=orbitals of the lowest energy must be filled first
Pauli Exclusion Principle=only two electrons are allowed for each orbital with opposite
spin
Hund’s Rule=When orbitals are equal in energy, one electron must be placed in each one
with same spin, before placing a second one in each orbital
-Different shells have different subshells:
Ex.
The p shell, where l=1, has three subshells, Px, Py, and Pz
E increases
Examples of Electron Configurations
1. Hydrogen 1s1
2. Boron 1s2 2s1 2Px1 2Py1
3. Zinc 1s2 2s2 2p6 3s2 3p6 4s2 3d10
4. Platinum 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6
6s2 4f14 5d8