1. Electromagnetic Radiation

2. Electromagnetic Radiation
Light
Quantized energy
Quantum theory and the atom

3. Light
Electromagnetic radiation

4. Light
Wave nature of light
Electromagnetic spectrum
Equations

5. Wave Nature of Light
All light is composed of an electric component and a magnetic component;
thus the term electromagnetic radiation

6. Wave Nature of Light
There are a few terms that we use to characterize light waves
Wavelength (l)
Units are meters (m)
Frequency (n)
Units are Hertz (Hz = seconds -1)
Amplitude

7. Wave Nature of Light
There are a few terms that we use to characterize light waves

8. Wave Nature of Light 3.0 x 108 m/s
Although light waves can have different wavelengths and frequencies, they all travel at the same speed;
the speed of light
3.0 x 108 m/s

9. Electromagnetic Spectrum
Remember when we learned about radiation energy we looked at the electromagnetic spectrum
Now we will apply the ideas of wavelength and frequency to the electromagnetic spectrum

10. Electromagnetic Spectrum

11. Electromagnetic Spectrum

12. Electromagnetic Spectrum
Visible light

13. Electromagnetic Spectrum
The frequency and wavelength of light are indirectly proportional
As one increases, the other decreases

14. Equations
The frequency and wavelength of light are indirectly proportional
When frequency and wavelength are multiplied together, they always equal the speed of light
Speed of light (c)
c = l n

15. Equations
If we know either the wavelength or the frequency of light, we can calculate the other one by rearranging the equation
Ex: If we know the wavelength, n = c/l
If we know the frequency, l = c/n

16. Quantized energy

17. Quantized Energy Particle nature of light
Emission and absorption spectra

18. Particle Nature of Light
Certain observations about light interacting with matter were not able to be described by the wave properties of light
Heated objects emit light at specific frequencies at a given temperature
When light of a certain frequency is shined on some metals, electrons are emitted

19. Particle Nature of Light
Max Planck, a German physicist, discovered that matter can only gain or lose energy in small specific amounts called quanta
A quantum is the minimum amount of energy that can be gained or lost by an atom

20. Particle Nature of Light
The energy (E) that is emitted by hot objects is related to the frequency (n) of the emitted radiation.
They are related by a number called Planck’s constant (h)
h = e-34 J x s
E = h n

21. Particle Nature of Light
h = e-34 J x s
Energy is always released in multiples of h n
(1 h n, 2 h n, 3 h n, )
E = h n

22. Particle Nature of Light
When light of a certain frequency is shined on a metal surface, electrons are ejected from the metal.
This phenomenon is known as the photoelectric effect

23. Particle Nature of Light
Photoelectric effect
Packets of light energy called photons
Energy of light is transferred to the electron increasing the electron’s kinetic energy

24. Particle Nature of Light
Photoelectric effect

25. Particle Nature of Light
Atomic emission spectra

26. Particle Nature of Light
Atomic emission spectra
Electricity passing through the neon gas in the glass tube
Neon atoms absorb that energy and become “excited”
The “excited” atoms release energy as light as they return back to their “ground” state
The atomic emission spectra for an element is the set of frequencies of the light emitted by the atoms as they return to their “ground” state

27. Particle Nature of Light
Atomic emission spectra
If the light emitted by an element is passed through a prism, the frequencies of the emitted light can be determined

28. Particle Nature of Light
Atomic emission spectra

29. Particle Nature of Light
Atomic emission spectra
Atomic emission spectra
Continuous emission spectra

30. Particle Nature of Light
Atomic emission spectra
Each element has its own unique emission spectra

31. Particle Nature of Light
Absorption spectra

32. Particle Nature of Light
Continuous vs. emission vs. absorption
“Excited” gas
“Ground state” gas

33. Particle Nature of Light
We don’t see the colors that are absorbed, only those that are reflected

34. Particle Nature of Light
We don’t see the colors that are absorbed, only those that are reflected

35. Particle Nature of Light

36. Particle Nature of Light
Why do you think this pattern occurs?

37. Quantum theory and the atom

38. Quantum Theory and the Atom
Bohr’s model of the atom
Electrons as waves
Heisenberg uncertainty principle

39. Quantum Theory and the Atom
Bohr used Planck’s idea of quantized energy and applied it to the atom
He proposed that electrons orbit nuclei only at specific distances from the nucleus

40. Quantum Theory and the Atom
Bohr atomic model

41. Quantum Theory and the Atom
Bohr atomic model
The orbital closest to the
nucleus corresponds to
the ground state
The orbitals further away
from the nucleus are
excited states

42. Quantum Theory and the Atom

43. Quantum Theory and the Atom
Energy associated with electron orbital transitions

44. Quantum Theory and the Atom
Energy associated with electron orbital transitions
DE = Ef – Ei
If E is absorbed, Ef > Ei
DE is positive
If E is emitted, Ef < Ei
DE is negative

45. Quantum Theory and the Atom
Energy absorbed or emitted can be in frequencies other than just visible light

46. Quantum Theory and the Atom
De Broglie proposed that electrons moving around the nucleus had wave-like behavior.
The wavelength associated with an electron depends on the mass and velocity of the electron
l = h / m v

47. Quantum Theory and the Atom
The idea of particle – wave duality applies to all matter, not just light and electrons
The mass of objects we can see are so large and the wavelengths are so small that we cannot see this effect
l = h / m v

48. Quantum Theory and the Atom
Heisenberg uncertainty principle
(for atomic scale particles)
It is impossible to know both the position and the velocity of a particle at the same time

49. Quantum Theory and the Atom
Anything we do to determine the location or velocity of an electron moves it from its original location and changes its velocity
We can know one or the other but not both
We talk about the probability for an electron to occupy a certain region around the nucleus
(so the fixed orbital proposed in the Bohr
model are impossible)