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Section 5-1

Section 5.1 Light and Quantized Energy. Compare the wave and particle natures of light. Define a quantum of energy, and explain how it is related to an energy change of matter. Contrast continuous electromagnetic spectra and atomic emission spectra.

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Section 5-1

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  1. Section 5.1 Light and Quantized Energy • Compare the wave and particle natures of light. • Define a quantum of energy, and explain how it is related to an energy change of matter. • Contrast continuous electromagnetic spectra and atomic emission spectra. radiation: the rays and particles —alpha particles, beta particles, and gamma rays—that are emitted by radioactive material Section 5-1

  2. Section 5.1 Light and Quantized Energy (cont.) electromagnetic radiation wavelength frequency amplitude electromagnetic spectrum quantum Planck's constant photoelectric effect photon atomic emission spectrum Light, a form of electronic radiation, has characteristics of both a wave and a particle. Section 5-1

  3. The Atom and Unanswered Questions • Recall that in Rutherford's model, the atom’s mass is concentrated in the nucleus and electrons move around it. • The model doesn’t explain how the electrons were arranged around the nucleus. • The model doesn’t explain why negatively charged electrons aren’t pulled into the positively charged nucleus. Section 5-1

  4. The Atom and Unanswered Questions (cont.) • In the early 1900s, scientists observed certain elements emitted visible light when heated in a flame. • Analysis of the emitted light revealed that an element’s chemical behavior is related to the arrangement of the electrons in its atoms. Section 5-1

  5. The Wave Nature of Light • Visible light is a type of electromagnetic radiation, a form of energy that exhibits wave-like behavior as it travels through space. • All waves can be described by several characteristics. Section 5-1

  6. The Wave Nature of Light (cont.) • The wavelength(λ) is the shortest distance between equivalent points on a continuous wave. • The frequency(f) is the number of waves that pass a given point per second. The unit for frequency is 1/sec or sec-1, which is known as a Hertz. • The amplitude is the wave’s height from the origin to a crest. Section 5-1

  7. The Wave Nature of Light (cont.) Section 5-1

  8. The Wave Nature of Light (cont.) • The speed of light (3.00  108 m/s) is the product of it’s wavelength and frequency c = λf. c = f Section 5-1

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

  10. The Wave Nature of Light (cont.) • Sunlight contains a continuous range of wavelengths and frequencies. • A prism separates sunlight into a continuous spectrum of colors. • The electromagnetic spectrum includes all forms of electromagnetic radiation. Section 5-1

  11. The Wave Nature of Light (cont.) Section 5-1

  12. The Particle Nature of Light • The wave model of light cannot explain all of light’s characteristics. • Matter can gain or lose energy only in small, specific amounts called quanta. • Max Planck (1900) Observed - emission of light from hot objects • Concluded - energy is emitted in small, specific amounts (quanta) • A quantum is the minimum amount of energy that can be gained or lost by an atom. • Planck’s constanthas a value of 6.626  10–34 J ● s. Section 5-1

  13. The Particle Nature of Light (cont.) • The photoelectric effect is when electrons are emitted from a metal’s surface when light of a certain frequency shines on it. Section 5-1

  14. The Particle Nature of Light (cont.) • Albert Einstein proposed in 1905 that light has a dual nature. • A beam of light has wavelike and particle like properties. • A photon is a particle of electromagnetic radiation with no mass that carries a quantum of energy. E = hv Ephoton = hv Ephoton represents energy.h is Planck's constant.v represents frequency. Section 5-1

  15. 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 Hz) E = 3.03  10-19 J Quantum Theory

  16. Atomic Emission Spectra • Light in a neon sign is produced when electricity is passed through a tube filled with neon gas and excites the neon atoms. • The excited atoms emit light to release energy. Section 5-1

  17. Atomic Emission Spectra (cont.) Section 5-1

  18. Atomic Emission Spectra (cont.) • The atomic emission spectrumof an element is the set of frequencies of the electromagnetic waves emitted by the atoms of the element. • Each element’s atomic emission spectrum is unique. Section 5-1

  19. A B C D Section 5.1 Assessment What is the smallest amount of energy that can be gained or lost by an atom? A.electromagnetic photon B.beta particle C.quanta D.wave-particle Section 5-1

  20. A B C D Section 5.1 Assessment What is a particle of electromagnetic radiation with no mass called? A.beta particle B.alpha particle C.quanta D.photon Section 5-1

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