1. Where are they in the atom?
THE ELECTRONS
Where are they in the atom?

2. A New Atomic Model
Rutherford/Bohr planet system model was an improvement over earlier models, but it was still not complete.
Where are the electrons really?
A new model evolved because of the similarities discovered between light and electrons.
This new connection led to revolution in science.

3. A New Atomic Model
The behavior of an electron can be modeled by the behavior of light.
We need to examine light closely then we’ll discuss the electron.
Light is a type of electromagnetic radiation, that travels through space as a wave.
Other examples are (x-rays, gamma-rays, and radio waves)

4. A New Atomic Model
All waves, whether they are water waves or electromagnetic waves, can be described in terms of four characteristics
Amplitude
Frequency
Wavelength
Speed

5. speed

6. A New Atomic Model Amplitude:
Is the height of the wave measured from the origin to its crest, or peak
The brightness, or intensity of light depends on the amplitude of the light wave.

7. A New Atomic Model Wavelength:
the distance between successive crests of the wave.
the distance that the wave travels as it completes one full cycle of upward and downward motion

8. A New Atomic Model Frequency:
Tells how fast the wave oscillates up and down.
Measured by the # of times a light wave completes a cycle of upward and down motion per sec.
When a radio station identifies itself it’s the frequency used
1 second

9. A New Atomic Model Speed:
Regardless of its wavelength, moves through space as a constant speed
3.00x108 m/s
Because light moves at a constant speed there is a relationship between frequency and wavelength

10. A New Atomic Model
It is a mathematical relationship between wavelength and the freq-uency of a wave.
The shorter the wavelength the higher the frequency
The longer the wavelength the lower the frequency
Calculated using the equation:

11. A New Atomic Model
speed of light
frequency c n = l
wavelength

12. A New Atomic Model
When white light passes through a prism or through raindrops you might have noticed that the
light can be separated into a continuous array or spectrum of colors

13. A New Atomic Model
The colors that combine to form white light are red, orange, yellow, green, blue, indigo, and violet (ROYGBIV)
The different colors have different wavelengths and frequencies
Shortest wavelength () & highest frequency () = violet
Longest  & lowest  = red

14. A New Atomic Model
Visible light only constitutes a very small portion of the total light spectrum.
The rest of the electromagnetic spec-trum is invisible to the naked eye
The next slide shows the relative positions of the various types of EM radiation in the EM spectrum

15. ELECTROMAGNETIC SPECTRUM
wavelength
frequency (Hz)
10-12m
10-9m
10-6m
10-3m
10-1m
1020
1018
1016
1014
1012
1010
108
GAMMA RAYS
X-RAYS
INFRARED
MICROWAVES
RADIO TV
ULTRAVIOLET

16. Visible Spectrum of the Electromagnetic Spectrum
INFRARED
ULTRAVIOLET
600nm
500nm
750nm
400nm

17. A New Atomic Model
Scientists soon discovered that elements also gave off an electro-magnetic spectra.
If you energize gaseous elements like hydrogen gas and then diffract the light given off by the excited element you see an electro- magnetic spectrum in the visible range

18. A New Atomic Model
But instead of the spectrum being continuous (one color bleeds into the next) the spectrum splits into a pattern of individual lines.
It’s not a mixture of all wavelengths, but a mixture of individual wavelengths
Only specific
wavelengths of color
in the mixture

20. A New Atomic Model
Scientist’s had a hard time explaining this line spectra, but finally along came a free thinking scientist named Max Planck,
Planck changed the face of science.
He developed a new theory that is the basis of modern physics
Quantum Theory

21. A New Atomic Model
Planck assumed that energy, instead of being given off continuously, is given off in little packets, or quanta.
The word quantum means a fixed amount
Think of it as bundles or flashes of energy
Also called photons

22. A New Atomic Model
Planck’s idea was that one quantum of energy (light) was related to its frequency by the equation: E = h 
The constant h (planck’s constant) has a value of x J-s, E is the amount of energy, and  is the frequency of the radiation.

23. A New Atomic Model
The energy in wave form that is abs-orbed or emitted by atoms, is res-tricted to certain quantities (quantized)
When we think of energy increasing, or being absorbed, we usually think of it increasing linearly.
energy

24. A New Atomic Model
In reality, at the atomic level, objects gain energy or lose energy in packag-es (quantum) of energy.
It’s more like steps than a ramp
Think about an accelerating car… if you push the gas pedal down you’re accustomed to your speed increasing continuously.
From 0 to 1 to 2 to 3 mph

25. A New Atomic Model
However, at the atomic level it might be like being at rest (0 mph) and abs-orbing energy until the right amount of energy has been achieved & then
10mph
20mph
30mph

26. A New Atomic Model
However, at the atomic level it might be like being at rest (0 mph) and abs-orbing energy until the right amount of energy has been achieved & then
BOOM! – you leap to 10 mph
10mph
20mph
30mph

27. A New Atomic Model
However, at the atomic level it might be like being at rest (0 mph) and abs-orbing energy until the right amount of energy has been achieved & then
BOOM! – you leap to 10 mph
BOOM! – you leap to 20 mph
10mph
20mph
30mph
A Quantum Leap

28. A New Atomic Model
You know from experience that cars don’t leap across speeds to accelerate
So how can Planck be right?
Planck’s theory works because of the size of planck’s constant (h).
Each quantum (step) is 10-34, so it feels like a continuous change of energy at the macroscopic level

29. A New Atomic Model
Planck’s theory of quantized energy was a revolutionary idea, but most scientists didn’t understand it.
Albert Einstein saw the potential of quantized energy and proposed it to be a new way of thinking about light.
He used Planck’s equation to explain the photoelectric effect.

30. A New Atomic Model
In the photoelectric effect, electrons are ejected from the surface of a metal when light shines on the metal.
For each metal, a minimum frequen-cy of light is needed to release e-
Red light can’t knock e- from metal,
but violet can easily

31. A New Atomic Model
Einstein guessed that light must exist as quantized energy for it to have the ability to eject E-s from metals
Light seems to act as a set of particles called a photons
When a photon strikes a metal atom, it transfers energy to an e- at the surface of the atom
Producing a tiny voltage

32. A New Atomic Model
Einstein reasoned that the energy (and thus the frequency) of the photon determines whether or not the photon has enough energy to knock an e- from the atom.
This helps explain why x-rays are damaging to organisms, while radio waves have low freq- uencies and aren’t hazardous.

33. A New Atomic Model
The idea that light is a wave that travels at the speed of light, is now coupled with the fact that light also seems to act as a particle
Light can be thought of as a tiny ball which can collide with an electron
Light exhibits the properties of both particles and waves.

34. A New Atomic Model
Knowing that atoms can gain or lose energy in chunks or quanta, brings us closer to answering the question of how electrons are arranged in the atom.
Remember earlier we said that if you split the light given off by hydrogen gas with a prism you see set of colored lines instead of a continuous spectrum.

35. A New Atomic Model This is true of every element
Every element, when excited, can emit light, which contains only certain wavelengths, giving each element a unique spectrum of lines.

37. A New Atomic Model
How do scientists explain the fact that each element is capable of emitting its own characteristic wavelengths of radiation (light)?
Is there some connection between the wavelengths an element emits and its atomic structure?

38. A New Atomic Model
Neils Bohr put Rutherford’s atomic model and Planck’s quanta theory together to begin to understand the line spectra of elements
Remember that Rutherford described the atom as a planetary system with the nucleus acting as the sun and the electrons orbiting much like planets.

39. A New Atomic Model
Bohr decided that the planetary model couldn’t adequately explain line spectra
Bohr reasoned that in order to get the single lines of energy released in line spectra the energy of the e- must be quantized.
The e- is allowed to have only certain orbits corresponding to different amounts of energy.

40. A New Atomic Model
Bohr labeled each energy level, or orbit, by a number, n.
He called an atom with all of its electrons occupying their lowest energy levels the ground state.
When an e- at any level absorbs the appropriate amount of energy, it leaps to a level of higher energy, A.K.A. excited state.

41. A New Atomic Model
In the excited state 1 or more elect-rons are higher in energy than they are accustomed to.
Eventually, the excited e- relaxes and releases its extra energy, and falls back to ground state
The energy released as the e- falls back to ground state might be given off as light in the visible range (color).

42. A New Atomic Model
The more energy absorbed by the electron the higher the leap in energy
The higher the leap - the farther the electron falls
The energy of the fall; leads to specific frequencies; therefore specific lines of color

44. A New Atomic Model
Bohr’s model worked well in its explanation of the spectrum of H
which was powerful evidence in support of his model.
However, Bohr’s model couldn’t explain the spectra of atoms with more than 1 electron,
It was a huge stepping stone to the modern model

45. A New Atomic Model
So let’s recap, until 1900, scientists believed that there was a clear distinction between energy & matter.
Remember Dalton’s statements of the atomic theory
Matter was thought of as a discrete, or quantized collection of particles.

46. A New Atomic Model
You can have 1, 2, or 8 million atoms of copper, but you can’t have 23.5 atoms or atoms.
At the same time, energy in the form of radiation was considered to be a collection of waves.
With specific amplitudes, frequencies, and wavelengths

47. A New Atomic Model
Now scientists are saying that light has the properties of waves & of discrete particles.
When light travels through space it has wavelike properties.
When it interacts with matter its behavior can be described as like a stream of particles.

48. A New Atomic Model Maybe scientists were wrong about matter too.
Maybe matter can act as not only a particle, but also as a wave.
Louis de Broglie reasoned that even particles of matter can behave like waves and at times exhibit the characteristics of a wave, much like light.

49. A New Atomic Model
He developed a mathematical rela-tionship between the mass & velocity of a moving particle and the wave-length it would exhibit,  = h/mv.
De Broglie’s equation predicts that all moving objects have wavelike behavior, but it is only notice- able in objects with a tiny mass.

50. A New Atomic Model
Today, scientists routinely take adv-antage of the wavelike properties of beams of electrons to magnify objects using electron microscopes.