Transcript Quantum Theory of the Atom

Models, Waves, and Light
Models of the Atom
• Many different models:
– Dalton-billiard ball model (1803)
– Thompson – plum-pudding model (1897)
– Rutherford – Nuclear model of the atom (1911)
– Bohr – uses quantized energy of the atom (1913)
– Quantum Mechanical Model of the Atom (1926)
• Each new model contributed
to the model we use today.
• Even our current model,
does not give us an exact
model of how electrons
interact.
Quantum Mechanical Model of the Atom
• Quantum Mechanical Model is the current description
of electrons in atoms
-does not describe the electron’s path around the
nucleus
• Quantum Mechanical Model is based on several ideas
-Schrodinger wave equation (1926) treats electrons as
waves.
-Heisenberg uncertainty principle (1927) states that it
is impossible to know both the velocity and position
of a particle at the same time.
Atomic Emission Spectrum
•When a current is passed through a vacuum tube of gas
at low pressure, a set of frequencies of the
electromagnetic waves are emitted by atoms of the
element
•Used to determine which elements are present in a
sample
•Used to determine which elements are present in a star
•Each element has a unique spectrum
•Only certain colors are emitted meaning only certain
frequencies of light are emitted
• A spectroscope that has a diffraction grating is needed
to see the atomic emission spectra, which acts similar
to a prism, separating different frequencies of light
Explanation of Atomic Spectra
•Electrons start at their
lowest energy level (ground
state)
•When an electron absorbs
energy it moves to a higher
energy level (excited state)
•When an e- drops back
down to a lower energy level
it gives off a quantum of
energy called a “photon”
•Only certan atomic spectra
are possible and emitted
Step 2
Step 1
Photons
• Behaves like a particle
• Behaves like a wave
Electromagnetic Spectrum
• Electromagnetic spectrum is the range of all
energies emitted from photons acting like
waves.
• If it is not in the visible light range, it may be
giving off other forms of electromagnetic
radiation like radio, microwaves, infrared, ultra
violet, x-rays, or gamma rays.
• Used to determine which elements are
present in a star (because stars are gases)
Electromagnetic Spectrum with Visible
Light Spectrum
How do Neon Signs work?
• They have
“excited” gases
in them.
Characteristics of a Wave
• Wavelength  (lambda) – shortest distance between
equivalent points on a continuous wave [Unit = meters]
• Frequency  (nu) – the number of waves that pass a given
point per second [Unit = 1/second = s-1 = Hertz (Hz)]
• Crest – Highest point of a wave
• Trough – Lowest point of a wave
• Amplitude (a)– height from its origin to its crest (highest
point) or trough (lowest point)
(Wavelength)
Amplitude
Amplitude
(Wavelength)
Wavelength and Frequency
• Wavelength () and frequency () are related
• As wavelength goes up, frequency goes down
• As wavelength goes down, frequency goes up
• This relationship is inversely proportional
Wavelength and Frequency cont.
c = 
= c / 
=c/
c
Speed of light

wavelength

frequency
c = 
8
Speed of light (c) = 3 x 10 m/s
Practice 1:
• Calculate the wavelength () of yellow light if
its frequency () is 5.10 x 1014 Hz. **Hz = 1/s
=c÷
 = 3 x 108 m/s ÷ 5.10 x 1014 Hz
-7
 = 5.88 x 10 m
c


Practice 2
• What is the frequency () of radiation with a
wavelength () of 5.00 x 10-8 m? What region
of the electromagnetic spectrum is this
radiation?
=c÷
8
-8
 = 3 x 10 m/s ÷ 5.00 x 10 m
 = 6.00 x 1015 1/s
c
ultraviolet region
(just barely)
 
How Much Energy Does a Wave Have?
E
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Energy of a wave can be calculated Energy
Use the formula E= h
h
Planck’s
constant frequency
E= Energy,  = frequency
h = Planck’s constant = 6.626 x 10-34 Joule . Sec
Joule is a unit for energy (J)
Energy and frequency are directly proportional,
as frequency increases, energy increases

Practice 3
• Remember that energy of a photon given off by
an electron is
E =h
• How much energy does a wave have with a
frequency of 2.0 x 108 s-1? ( h = 6.626 x 10-34 Js)
E =h
E = (6.626 x 10-34 Joule  s)(2.0 x 108 s-1)
E = 1.3 x 10-25 Joule
Visible Light, Frequency, and Energy
• Red: longest wavelength (),
smallest frequency ()
• Red: frequency smallest (),
least amount of energy (E)
• Violet: smallest wavelength (),
largest frequency ()
• Violet: frequency largest (),
greatest amount of energy (E)