Waves & Particles Ch. 6 - Electrons in Atoms

A. WAVES zLight: a form of electromagnetic radiation yComposed of perpendicular oscillating waves, one for the electric field and one for the magnetic field xAn electric field is a region where an electrically charged particle experiences a force. xA magnetic field is a region where a magnetized particle experiences a force. zAll electromagnetic waves move through space at the same, constant speed. y3.00 × 10 8 m/s = the speed of light © 2014 Pearson Education, Inc.

A. WAVES © 2014 Pearson Education, Inc.

A. Waves zWavelength ( )(lambda) - length of one complete wave ymeters (m) or nanometers (nm) zFrequency ( ) (nu) - # of waves that pass a point during a certain time period yhertz (Hz) = 1/s or s -1 zAmplitude (A) - distance from the origin to the trough (bottom of the wave) or crest (top of the wave).

A. Waves A greater amplitude: (>intensity) greater frequency: (color) crest trough

Electromagnetic Spectrum LOWENERGYLOWENERGY HIGHENERGYHIGHENERGY

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B. EM Spectrum LOWENERGYLOWENERGY HIGHENERGYHIGHENERGY ROYG.BIV redorangeyellowgreenblueindigoviolet

B. EM Spectrum zFrequency & wavelength are inversely proportional by this equation: c = c:speed of light :wavelength :frequency Which means: Long wavelength, low frequency Short wavelength, high frequency

B. EM Spectrum GIVEN: = ? = 434 nm = 4.34  m c = 3.0  10 8 m/s WORK : = c = 3.0  10 8 m/s 4.34  m = 6.91  Hz zEX: Find the frequency of a photon with a wavelength of 434 nm.

B. EM Spectrum GIVEN: = ? = MHz =  10 8 Hz c = 3.00  10 8 m/s WORK : = c = 3.00  10 8 m/s  10 8 s -1 = m zEX: Z103 has a frequency of MHz. What wavelength do they broadcast at?

C. Quantum Theory zPlanck (1900) yObserved - emission of light from hot objects; different colors (different ’s) at different temperatures. yConcluded - energy is emitted in small, specific amounts (quanta) yQuantum - minimum amount of energy change

C. Quantum Theory zPlanck (1900) vs. Classical TheoryQuantum Theory

C. Quantum Theory zEinstein (1905) yObserved - photoelectric effect – light shining on a metal surface causes the surface to emit electrons

C. Quantum Theory zEinstein (1905) yConcluded - light has properties of both waves and particles “wave-particle duality” yPhoton - particle of light that carries a quantum of energy; energy of violet photons is greater than energy of red.

C. Quantum Theory E:energy h: Planck’s constant : frequency Which means: High frequency, high energy Low frequency, low energy zThe energy of a photon is directly proportional to its frequency by this equation:

C. Quantum Theory GIVEN: E = ? = 4.57  Hz h =  J·s WORK : E = h E = (  J·s ) ( 4.57  Hz ) E = 3.03  J zEX: Find the energy of a red photon with a frequency of 4.57  Hz.

C. Quantum Theory GIVEN: E = ? = ? But =c/ = c = 3.0 x 10 8 m/s 8.3 x m = 3.6 x10 14 /s h =  J·s WORK : E = h E = (  J·s ) ( 3.6  Hz ) E = 2.4  J zEX: Find the energy of a photon with a wavelength of 8.3  m.

D. Bohr Model zBohr (1911) was the first to see the connection between the wavelengths an element emits and its atomic structure (the electron). zHe postulated that to get spectral lines, the energy of the electron must be quantized.

D. Bohr Model Limitations ze - exist only in orbits with specific amounts of energy called energy levels which are described by quantum numbers. zTherefore… ye - can only gain or lose certain amounts of energy yonly certain photons (particles of light) at specific wavelengths are produced

D. Bohr Model zEnergy of photon (color of light) depends on the difference in energy levels zBohr’s calculated energies matched the visible lines for the H atom

D. Bohr Model e- at ground state e- at excited state ENERGY IN PHOTON OUT

Spectra and Space

zhttp://youtu.be/d8hpUtRnsYchttp://youtu.be/d8hpUtRnsYc zhttp://youtu.be/n_KyYFYNvpIhttp://youtu.be/n_KyYFYNvpI zAtmosphere: To learn a planet's atmosphere, we examine the spectrum of starlight passing through its atmosphere. Missing frequencies are clues, indicating elements or compounds that absorb light at those frequencies are present in the atmosphere. For example, if the light frequencies corresponding to methane and carbon monoxide are missing from an analysis of the starlight, the atmosphere contains methane and carbon monoxide, which absorbed the missing light.

E. Line-Emission Spectrum zEmission Spectrum– contain only certain colors or wavelengths on a black background; unique for each element, the “atomic fingerprint”. zAbsorption Spectrum – black lines that appear on a rainbow background; used to determine atmosphere and star make-up. zContinuous Spectrum – contains all the colors of the spectrum For example: sunlight, some light bulbs

Emission versus Absorption Spectra Spectra of Mercury © 2014 Pearson Education, Inc.

E. Line-Emission Spectrum zEach element has a unique bright-line emission spectrum which can be seen with a spectroscope that focuses a narrow beam of light on a prism or through a diffraction grating, sorting the light by wavelength. This allows us to see the wavelengths and colors associated with each element. Helium

EM Spectrum(draw and color on another sheet of paper that will go into your notes, pp ) LOWENERGYLOWENERGY HIGHENERGYHIGHENERGY