1. Chapter 7 Electronic Structure of Atoms

2. The Wave Nature of Light The electronic structure of an atom refers to the arrangement of the electrons. Visible light is a form of Electromagnetic radiation (EMR). Radiation carries energy through space EMR is characterized by its wave

3. Wave Properties All waves have a characteristic wavelength, λ (lambda), and amplitude, A. The frequency, ν (nu), of a wave is the number of cycles which pass a point in one second. The units of ν are Hertz. (1Hz = 1/s)

4. The speed of EMR is always the same no matter what the wavelength or frequency. EMR speed is the speed of light. c is the symbol for the speed of light C = 3.0 x 10 8 m/s

5. The relationship between frequency ( ν ) and wavelength ( λ )is shown by the equation c = λ ν Where c = the speed of light = 3.0 x 10 8 m/s λ = the wavelength of the wave ν = the frequency of the wave (Hz)

6. Frequency and wavelength are inversely related. Since the speed of the wave is constant (3.0 x 10 8 m/s), if the frequency is known, the wavelength can be determined. Likewise, if the wavelength is known, the frequency can be determined.

7. Light as Electricity and Magnetism oMax Planck determined mathematically that light is both magnetism and electricity. oHe determined the Energy in a photon is directly related to its frequency.

8. oIf the frequency is multiplied by Planck’s constant (6.6261 x 10 -34 J- s), the Energy of the photon can be determined.

9. oThis relationship is represented in the formula E=h ν Where  E = Energy  h = 6.6261 x 10 -34 J.s (Planck’s constant)  ν = frequency

10. How does this relate to atomic models? Remember these guys? DALTON’S MODEL – Atom was dense sphere – Indestructible – Smallest particle of matter – Neutral charge

11. Thomson’s Model Thomson had the Plum Pudding Model. Negative particles interspersed in positive atom, NEUTRALLY CHARGED. Changed Dalton’s Model: Atom is NOT smallest particle of matter.

12. Rutherford’s Model PROBLEMS Could not explain the chemical properties of the elements. Why do metals give off characteristic colors when heated in a flame? When heated iron glows red, then yellow, then white. WHY? Dense positive center with electrons outside the nucleus.

13. BOHR MODEL GOAL: To improve Rutherford’s Atomic Model

15. QUANTUM MECHANICAL MODEL OF THE ATOM The quantum mechanical model is a way of describing the atom through electron movement. Electrons are arranged in orbitals (path the electron follows) in Energy levels (distance from the nucleus) around the nucleus.

16. If the electrons gain a photon (specific amount) of energy they can travel to higher energy levels. The energy level the electron travels to will be determined by the amount of energy in the photon.

17. The electron cannot maintain this higher energy level and eventually returns to a lower level. The energy is released as it travels down in the form of EMR. The color you see depends on the wavelength of the light released.

18. Determining the Energy of the photon. To determine the Energy of the photon released, we use the formula E=h ν

19. Example: PROBLEM: What is the energy of a photon with a frequency of 3.7 x 10 7 Hz? SOLUTION: Use the formula E=h ν. E = ? h= 6.6261 x 10 -34 J-s ν = 3.7 x 10 7 Hz E= ( 6.6261 x 10 -34 J-s ) (3.7 x 10 7 1/s)= 24.51657 x 10 27 J Then 24.51657 is not a number between 1 and 10. 2.451657 x 10 28 J