1. Quantum Physics

3. What makes one atom different from another? atom The amazing colors produced in fireworks are a result of the different types of atoms that are used. The colors depend on the chemical characteristics of the elements used to make them.

4. What makes one atom different from another?atom The amazing colors produced in fireworks are a result of the different types of atoms that are used. The colors depend on the chemical characteristics of the elements used to make them.

5. Atomic Spectra There are discrete energy levels for each electron in each atom (quantum mechanics) Absorption of energy results in a transitions to a higher energy level. A transition back to a lower level produces a photon of light. The frequency of the emitted photon is determined by the difference in the energy levels. E photon = hf = E 2 – E 1 Each frequency is a different color.

6. Atomic Spectra Since the electrons levels are unique for each element, each element produces a unique spectra of colors when supplied energy. Spectra for Neon

7. Atomic Spectra each element produces a unique spectra of colors viewed through a diffraction grating Spectra for Neon

8. The incandescence from the elements occurs when solid particles are heated in the flame to extremely high temperatures. This releases excess energy in the form of light. The higher the temperature, the shorter the wavelength at which light is emitted, and the nearer it tends toward the blue end of the colored spectrum. This is why blue colored fireworks are so hard to synthesize, as they only occur at very high temperatures. MetalColor StrontiumRed CopperBlue BariumGreen SodiumYellow/Orange CalciumOrange GoldIron

10. The Hydrogen Atom: ONE electron! The frequency of the emitted photon is determined by the difference in the energy levels. E photon = hf = E 2 – E 1

11. Now you try one…. Get out your calculators!! The energized electron in Hydrogen makes a transition from n = 3 with an energy of -1.5 eV down to its ground state where its energy is -13.6 eV. What is the frequency of the emitted photon? E photon = E 2 – E 1 and E photon = hf E photon = -1.5 eV – (-13.6 eV) = 12.1 eV E photon = 12.1 eV = hf(h = 4.14 x 10 -15 eV·s ) f = 12.1 eV ÷ 4.14 x 10 -15 eV·s = Frequency, f = 2.92 x 10 15 Hz Is this visible light?? Use c = f to find the wavelength. wavelength, = 1.02 x 10 -7 = 102 nm This is NOT visible light- it is UV.

12. Hydrogen Emission The energy of the electron is given by E = 1.Find the Energy of the Hydrogen electron from n = 1 to n = 7. 2. Find the Energy of each photon emitted (E photon =  E) for these transitions: 4 to 15 to 26 to 37 to 4 3 to 14 to 2 5 to 36 to 4 2 to 13 to 24 to 35 to 4 3. Find the wavelength for each of those photons and determine what type of electromagnetic wave they are.

14. Light behaves like a wave AND like a particle The first clear demonstration of the particle-like behavior of light was in The Photoelectric Effect Albert Einstein won the Nobel Prize in Physics for his explanation of the Photoelectric Effect.

15. Electromagnetic waves striking a metal surface can liberate electrons from its surface. The photons must have enough energy (high enough frequency) for this effect to occur. The energy of the “photoelectrons” liberated from the surface depends on the frequency of the photon. Increasing the intensity (brightness) of the light increases the number of photoelectrons emitted, but not the energy of each electron. The Photoelectric Effect

16. When will Photoelectrons be produced?Photoelectrons

18. Now you try some: If the threshold wavelength for a particular metal is 320 nm, what is the metal’s work function? First, find the threshold frequency using c = f Threshold frequency, f o = 9.38 x 10 14 Hz Now find the work-function: hf o = W o Wo = 3.88 eV

19. What if a 450 nm light hit a surface with a work function of 2.36 eV. What will be the kinetic energy of the photoelectron? First, find the frequency of the 450 nm light. f = 6.67 x 10 14 Hz Now, using conservation of energy: hf = W o + Kinetic energy So K = hf – Wo K = 0.40 eV