later contributors to atomic theory pg. 90-94 2 nd note taking sheet ©2011 university of illinois...

Later Contributors to Atomic Theory

Pg. 90-94

2nd Note Taking Sheet

©2011 University of Illinois Board of Trustees • http://islcs.ncsa.illinois.edu/copyright

Interaction of Light and Matter

• In order to understand the contributions of the next scientist, it is important to understand the characteristics of light and how it can interact with matter.

• Other names for light are radiant energy or electromagnetic radiation (emr for short).

• In the early 1900s there were observable phenomena involving light and its interaction with matter that could not be explained.


Electromagnetic Radiation

• Light consists of an oscillating electric field at right angles to an oscillating magnetic field, thus its name (emr).


Characteristics of Light (p.92-93)

• In order to understand the contributions of the next scientist, it is important to understand the characteristics of light and how it can interact with matter.

• At this time in history scientists thought of light as waves that propagated (moved) outward perpendicular from the source.

• In a vacuum scientists knew that light in a vacuum traveled at 2.998 x 108 m/s.

• This maximum limit on the speed of light is a universal constant represented by the letter “c”.

• All types of light travel at this speed in a vacuum.• If light travels through a denser material it will slow down

and different energies of light will be bent differently.


Characteristics of Light Continued• The electromagnetic radiation spectrum is

all the possible energies of light.– Note that humans can see only a very small portion of

emr called the visible range.


Characteristics of Light ContinuedWavelength

• Light of a certain energy has a characteristic frequency and wavelength.

• A wavelength is the distance from

peak to peak or

trough to trough.

• It is a length

measurement.


Characteristics of Light ContinuedFrequency

• The frequency of light is the number of wavelengths that can pass through a point in a second.

• Frequency has units of 1/s or s-1 or Hertz (Hz)

• The higher the

frequency the

higher the energy

of the light©2011 University of Illinois Board of

Trustees • http://islcs.ncsa.illinois.edu/copyright

Characteristics of Light ContinuedSpeed

• In a vacuum all light travels at 2.998 x 108 m/s

• The speed of light, its frequency and wavelength are all related by the equation:

C = λ ∙ νWhere λ (“lambda”) is wavelength and

ν (“nu”) is the frequency

• Note that if frequency becomes greater the wavelength becomes smaller.


Electromagnetic Radiation Spectrum


Characteristics of Light ContinuedEnergy

• In 1901 Max Planck found that atoms can only adsorb and emit energy in distinct quantities; this showed that energy is quantized. He also determined that the energy of the light is given by the equation

E = h ∙ νWhere E is energy (J)

h is Planck's constant = 6.626 x 10-34 J∙sV is the frequency in Hz or 1/s or s-1 or cycles/sec


Inexplicable New Evidence

• Photoelectric effect occurs when light hits a piece of metal and the metal ejects an electron.

• The energy of the light had to be at least a certain minimum value that was different for different metals.

• Black body radiation.


Albert Einstein (1905)• To explain the photoelectric effect, in 1905

Einstein suggested that light can behave like particles as well as waves.

• The way in which you consider light depends on the phenomenon you are observing. This is known as the dual nature of light.

• Light can be considered to be little discrete packets of energy called photons.


Hydrogen Line Emission Spectrum

• Scientist were very surprised that they didn’t get a continuous spectrum for the light emitted by hydrogen.©2011 University of Illinois Board of Trustees •

http://islcs.ncsa.illinois.edu/copyright

There is a fingerprint line emission spectrum for all the elements.

Use the spectroscope to see the emission spectrum of other elements.


Neils Bohr (1913)• Explained the

unexpected result of a hydrogen line emission spectrum.

• Proposed a model of the atom in which the electrons have quantized energy.

• Electrons of an atom could only be certain allowed distances from the nucleus which corresponded to specific energy values.


Bohr Continued

• When electrons are in their lowest energy state, Bohr called this their ground state.

• He said the when electrons are in a higher energy orbit, they are in the excited state.

• Energy is absorbed to excite an electron and released when an electron goes back to its ground state.

• Energy is released in the form of light.


Hydrogen Line Emission Spectrum


Louis DeBroglie (1923)

• In writing his doctoral thesis Louis DeBroglie suggested that electrons could behave like waves as well as particles.

• In fact he stated that all matter has a wave nature given by the formula

λ = h/mv Where m is the mass and v

is the speed.


Louis DeBroglie Continued

• This meant that an electron “orbiting” the nucleus can be thought of as a wave. Each electron moves with a characteristic energy.

• The energy of the electron depends on the wavelength.

• All matter has a characteristic wave called a matter wave – even you!


Erwin Schrodinger (1926)

• Schrodinger developed a wave theory about how electrons can exist in atoms.

• His wave theory explains the different energy states of an electron and is based on electrons behaving as waves.


Warner Heisenberg (1927)

• Realized that if electrons behave as waves their existence is more spread out and it is impossible to know exactly where the electron is or how fast it is moving.

• This is a statement of the uncertainty principle.


later contributors to atomic theory pg. 90-94 2 nd note taking sheet ©2011 university of illinois...

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