I. Waves and Particles

1. Electrons in Atoms I. Waves and Particles

2. A. A New Atomic Model • Rutherford model of the atom • Dense positively charged nucleus • Mostly empty space • Did not explain where the electrons are located around the nucleus • Did not explain why negative electrons did not move to the p+ in the nucleus and collapse atoms

3. A. A New Atomic Model • Prior to 1900 : • Electrons are particles (concentration of energy and other properties in space and time) • Light is waves (energy spread out over a larger region of space and time; an oscillation that moves outward from a source.

4. A. A New Atomic Model • New atomic model emerged as a result of experimentation with absorption and emission of light by matter. • Studies revealed a relationship between light and an atom’s electrons. • Light was shown to exhibit both particle and wave-like behaviors. • Electrons were also shown to exhibit dual wave-particle nature.

5. B. Waves • Velocity (c) – Unit: m/s • Amplitude (A) - distance from the origin to the trough or crest. Unit will be length (m, …) • Wavelength () - length of one complete wave ; peak-to-peak distance. Unit: m, nm… • Frequency ( or f ) - # of waves that pass a point during a certain time period • hertz (Hz) = 1/s or s-1

6.  crest A A origin trough  B. Waves greater amplitude (intensity)

7. B. Waves • Frequency & wavelength are inversely proportional c =  c: speed of light (3.00  108 m/s) : wavelength (m, nm, etc.) : frequency (Hz)

8. WORK:  = c   = 3.00  108 m/s 2.73 x 1016 s-1 B. Waves • EX: Light near the middle of the ultraviolet region of the EM spectrum as a frequency of 2.73 x 1016 s-1. Calculate its wavelength. GIVEN:  = 2.73 x 1016 s-1  = ? c = 3.00  108 m/s = 1.10 x 10-8 m

9. WORK:  = c   = 3.00  108 m/s 4.34  10-7 m B. Waves • EX: Find the frequency of light with a wavelength of 434 nm. GIVEN:  = ?  = 434 nm = 4.34  10-7 m c = 3.00  108 m/s = 6.91  1014 Hz

10. C. Electromagnetic Spectrum • Electromagnetic radiation – a form of energy that exhibits wavelike behavior as it travels through space • Electromagnetic spectrum – all forms of electromagnetic radiation together

11. R O Y G. B I V red orange yellow green blue indigo violet C. EM Spectrum HIGH ENERGY LOW ENERGY

12. C. EM Spectrum HIGH ENERGY LOW ENERGY

13. C. EM Spectrum • Spectroscopy – branch of science that studies the interaction of light and atoms. • Spectrum – pattern of  or  when electromagnetic radiation is separated into its parts. • Spectroscope – instrument used to measure the wavelength of light.

14. C. EM Spectrum • Continuous spectra – use a diffraction grating to separate the wavelengths into the visible light spectrum. Shows all wavelengths in a given range. • Example : • visible light (400 nm – 700 nm)

15. C. EM Spectrum • Emission (bright line) spectra • Each line = different wavelength of light. • Lines represent energy emitted as e- fall from excited state to lower/ground state (from high energy levels to lower energy levels) • Usage – analyze substances for elements present. Each emits its own color. (Stars/astronomy)

16. C. EM Spectrum

17. C. EM Spectrum • Absorption (black line) spectra – shows the fraction of incident radiation absorbed by the material over a range of frequencies.

18. C. EM Spectrum • Ground state vs. excited state • Ground state – Electrons in the atom are in the lowest energy levels. • Excited state – Electrons in the atom are in higher energy levels. Electrons become “excited” when they gain enough energy to jump to a higher energy level in the atom. • Example: flames, spectral tubes

19. D. Waves vs Particles • Waves can bend around small obstacles. • Waves can fan out from pinholes. • Particles effuse (trickle out) from pinholes. • Ex. Balloon gradually deflates.

20. D. Waves vs Particles

21. E. Particle Behavior of Light • Max Planck (1900) • Observed - emission of light from hot objects • Concluded - energy is emitted in small, specific amounts (quanta = bundle of energy)

22. Classical Theory Quantum Theory E. Particle Behavior of Light • Planck (1900) vs.

23. E. Particle Behavior of Light • Einstein (1905) – observed the photoelectric effect. Electromagnetic radiation strikes the surface of the metal, ejecting electrons from the metal, creating an electrical current.

24. E. Particle Behavior of Light • Einstein (1905) • Concluded - light has properties of both waves and particles “wave-particle duality” • Light moves like a wave, but transfers energy like a stream of particles.

25. E. Particle Behavior of Light • Photon – bundle of energy given off as light. A particle of electromagnetic radiation having zero mass and carrying a quantum of energy. • Quantum - minimum amount of energy that can be lost or gained by an atom

26. E. Particle Behavior of Light • The energy of a quantum of energy is proportional to its frequency. E: energy (J, joules) h: Planck’s constant (6.6262  10-34 J·s) : frequency (Hz) E = h

27. E. Particle Behavior of Light • EX: Find the energy of a red photon with a frequency of 4.57  1014 Hz. GIVEN: E = ?  = 4.57  1014 Hz h =6.6262  10-34 J·s WORK: E = h E = (6.6262  10-34 J·s) (4.57  1014 s-1) E = 3.03  10-19 J