2024 Fall Unit 2 Notes PDF

Photons Photons play an important role in our modern world. In hospitals, high-energy photons are used in treatments to reach tumors without damaging surrounding tissues. In gamma knife radiation therapy, gamma photons are used to kill cancer cells or reduce tumor size. read pit...

Photons Photons play an important role in our modern world. In hospitals, high-energy photons are used in treatments to reach tumors without damaging surrounding tissues. In gamma knife radiation therapy, gamma photons are used to kill cancer cells or reduce tumor size. read pits on compact discs (CDs) and digital versatile discs (DVDs) scan bar codes on merchandise labels The light emitted, when atoms are heated, is a stream of particles called photons. A photon is a packet of energy (known as a quantum). has the characteristics of both a particle and a wave. Wave equation: c = λν © 2014 Pearson Education, Inc.  Electromagnetic Spectrum The electromagnetic spectrum is an arrangement of different types of electromagnetic radiation from longest to shortest wavelength. © 2014 Pearson Education, Inc.  Electromagnetic Radiation We experience electromagnetic radiation when we listen to a radio. use a microwave oven. see colors in a rainbow. have an X-ray taken. Infrared radiation with wavelengths of about 1 micrometer keeps food at proper serving temperature. Microwaves with wavelengths of about 1 centimeter heat water molecules in food. All types of electromagnetic radiation, including light / photons, consist of particles that move as waves of energy. © 2014 Pearson Education, Inc.  longer wavelengths: – radio waves and cellular phones, while shorter wavelengths: – infrared lights, ultraviolet light, and heat lamps. Visible light: 400 to 700 nm © 2014 Pearson Education, Inc.  Wavelength and Frequency Wavelength (λ, lambda) is the distance from a crest or trough in a wave to the next crest or trough. Measured in meters. Frequency (ν, nu) is the number of times the crests of a wave pass a point in 1 second. Measured in per seconds (s-1 or 1/s) All electromagnetic radiation travels at the speed of light (c), 3.00  108 m/s. © 2014 Pearson Education, Inc.  Wave Equation Wave equation: c = λν relationship of the speed of light (m/s) to wavelength (m)(λ) and frequency (s−1)(ν). The speed of light (c) is constant. As the wavelength increases, the frequency decreases and vice versa c λ= what happens to λ as ν gets larger? ν c ν= what happens to ν as λ gets larger? λ © 2014 Pearson Education, Inc.  Inverse Relationship of λ and ν The inverse relationship between wavelength and frequency means that different types of electromagnetic radiation have different wavelengths and frequencies. longer wavelengths have lower frequencies. shorter wavelengths have higher frequencies. © 2014 Pearson Education, Inc.  Direct Relationship of Energy and Frequency Energy of electromagnetic radiation: – directly related to frequency – inversely related to the wavelength. As the wavelength of radiation increases – frequency decreases – energy decreases. © 2014 Pearson Education, Inc.  If blue light has a wavelength of 450 n m , is the wavelength of red light greater or ano eter less than 450 n m ? Which color is higher in energy? ano eter © 2014 Pearson Education, Inc.  Select diagram A, B, or C that: a. has the longest wavelength b. has the shortest wavelength c. has the highest frequency d. has the lowest frequency e. has the highest energy f. has the lowest energy © 2014 Pearson Education, Inc.  Compare the frequency and wavelength of photons of ultraviolet light with that of infrared light. Ultraviolet light:wavelength, 10−8 m frequency, 1016 Hz Infrared light: wavelength, 10−4 m frequency, 1013 Hz Ultraviolet light has shorter wavelengths and higher frequencies than infrared light. © 2014 Pearson Education, Inc.  Atomic (Emission) Spectra When white light passes through a prism, a continuous spectrum, is produced. Heating atoms of an element also produces light, such as the yellow color of sodium streetlights. red color of a neon sign. Colors are produced when electricity excites electrons in noble gases. © 2014 Pearson Education, Inc.  Atomic Spectra Heated elements produce an atomic spectrum, which consists of different colors separated by dark areas; it does not produce a continuous spectrum. The lines produced are associated with changes in the energies of electrons. Specific wavelengths of light are produced by heated elements. © 2014 Pearson Education, Inc.  Changing Energy Levels When electrons change from a lower to a higher energy level, they absorb the energy equal to the change in energy levels. When electrons change from a higher to a lower energy level, they emit energy equal to the change in energy levels. © 2014 Pearson Education, Inc.  Electrons and Energy Levels In an atom, each electron has a specific energy level. energy levels are assigned values called principal quantum numbers (n) (n = 1, n = 2...). Electrons in lower energy levels are closer to the nucleus. Principal Quantum Number (n) (Low to high Energy) 1