Quantum Theory

1
Quantum Theory

• Objectives
• Compare the particle to wave model of light
• Analyze the path of the electron
• Contrast the spectra
• Identify the quantum numbers that lead to the
  locations of the electrons
• Write electron configurations and
• Define the parts of the configuration such as the
  valence

2
Facts

• So, we know what is in the nucleus.
• Protons and neutrons
• Most of the mass of the atom lies here
• How do the electrons exist outside the nucleus?
• How do electrons occupy the space surrounding the
  nucleus?
• How do they avoid the laws of physics? (repulsion)

3

• The electromagnetic spectrum (above) illustrates
  the visible light portion of electromagnetic
  radiation.
• What energy type comes after the violet?
• What energy type comes after the red?
• Which one has the most energy? Least?

4
Fact Sheet 2

• Electromagnetic waves can be described by their
  wavelengths, energy, and frequency.
• All three of these things describe a different
  property of light, yet they are related to each
  other mathematically.
• Wavelength is usually measured in meters (m).
• Frequency is the number of cycles of a wave to
  pass some point in a second. The units of
  frequency are thus cycles per second, or Hertz
  (Hz).

• All light travels at the same speed, but each
  color has a different wavelength and frequency.
  It is their different wavelengths that cause the
  different colors of light to separate and become
  visible when passing through a prism.

5
Lets analyze the wave
6

• Waves in the electromagnetic spectrum vary in
  size from very long radio waves the size of
  buildings, to very short gamma-rays smaller than
  the size of the nucleus of an atom

7
Illustration of frequency
Look at the illustration of the visible spectrum
above. Can you guess which color has the longest
wavelength?
8
Frequency vs. Wavelength

• Based on prior knowledge, just how do these two
  relate?
• Why can we use these terms to discuss anything on
  the electromagnetic spectrum?

9
Mathematical Relation
Speed Wavelength Frequency
10
LAB Obj You will construct a simplified model
of different light waves in order to determine a
constant relationship between wavelength and
frequency.

• Materials
• set of red, green and violet (purple) pencils
• manila folder meter stick or metric ruler 
• pair of scissors 
• 4 books 
• watch with second hand 
• one strip of masking tape 
• extra pencil

11

• We already know that light acts like a wave, but
  did you know that sometimes it acts like a
  particle? We call particles of light photons.
  Low-energy photons, like radio photons, tend to
  behave more like waves, while higher energy
  photons (i.e. X-rays) behave more like particles.
  That's another reason that we don't talk about
  X-ray waves very often. Instead we talk about
  individual X-rays and their energies.

12
Atomic Emission Spectra

• When matter is heated, it gives off light. For
  example, turning on an ordinary light bulb causes
  an electric current to flow through a metal
  filament which heats the filament and produces
  light
• The electrical energy absorbed by the filament
  excites the atoms' electrons causing them to
  'wiggle'. This absorbed energy is eventually
  released from the atoms in the form of light.

13
Neon line spectra

• Bohr knew that when pure elements were excited by
  heat or electricity, they gave off distinct
  colors rather than white light. This phenomenon
  is most commonly seen in modern day neon lights,
  tubes filled with gaseous elements (most commonly
  neon). When an electric current is passed through
  the gas, a distinct color (most commonly red) is
  given off by the element. When light from an
  excited element is passed through a prism, only
  specific lines (or wavelengths) of light can be
  seen. These lines of light are called line
  spectra.

                                                            
14

• When an atom is excited, such as during heating,
  electrons can jump to higher levels
• Bohr hypothesized that electrons occupy specific
  energy levels.
• When the electrons fall back to lower energy
  levels, precise quanta of energy are released as
  specific wavelengths (lines) of light.

15

• The comfy spot for an electron is on the ground
  state which is the lowest energy level in the
  atom
• Key to Bohr's theory was the fact that the
  electron could only 'jump' and 'fall' to precise
  energy levels, thus emitting a limited spectrum
  of light. These pockets of energy are called
  quanta.

16

• Bohr also predicted that those levels had limits
  to the number of electrons each could hold.
• This leads us to the Quantum Theory