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Chemistry Preceptor Review exam 2

# Chemistry Preceptor Review exam 2 - Light By Doug Collins...

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2/6/11 Light By: Doug Collins and Jessica Williman

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2/6/11 What is Light, Anyway? Light is defined as electromagnetic radiation characterized by a wave- like function. Waves can be described by their wavelength ( ) and frequency ( ) λ ν For all waves, the product of frequency and wavelength gives the velocity of the wave. V= νλ Light always travels at a constant
2/6/11 Wavelength Wavelength, (lambda), is defined as the λ length between two identical parts of the wave (crest to crest, trough to trough, etc.) and is measure in meters (m)

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2/6/11 Frequency and Speed of Light
2/6/11 Energy of a Photon The energy of a single photon is calculated by the equation E=h ν E=energy of a photon measured in Joules (J) h= Planck's Constant = 6.626 x 10 ³ J•s ⁻ ⁴ =frequency measured in Hz ν E (J) =h (J•s) • (Hz) ν Notice the direct relationship between energy

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2/6/11 Energy of a Photon A quick rearrangement of the equation gives us the energy in terms of wavelength E = hc/ λ Notice the indirect relationship between energy and wavelength. The higher the energy, the smaller the wavelength and vice versa.
2/6/11 Useful Equations

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2/6/11 γ-rays X-rays U V VISIB LE Infrar ed microw ave Radio/ TV Long waves ROY G BIV Energy INCREASES VIB G YOR
2/6/11 Functions of Light -ray - γ destroys tissue X-ray - penetrates tissue – knocks out e’s UV - moves e’s; breaks bonds Visible - moves e’s inside of atoms (jumps) IR - causes molecules to vibrate- no e jump Microwave - spins molecules; rotates bonds Radio/TV - passes through tissue will flip the nucleus of H MRI Long waves - communications through the earth Taos,NM HUMMMM ELF (extreme low freq)

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2/6/11 Emission Spectra Electrons of a particular element respond to specific wavelengths. They absorb light at theses wavelengths and release light at these wavelengths. The emission spectrum of Hydrogen is below.
2/6/11 Emission Spectrum (cont.) Niels Bohr suggested that electrons in atoms can only exist in certain discrete orbits with certain discrete energy levels, called quantized energy states. The transition of an electron from one orbit to another will always require some specific fixed energy.

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2/6/11 Emission Spectrum (cont.) A photon with a particular energy will raise an electron to a higher orbital The energy of the photon MUST exactly match the energy difference between the
2/6/11 Emission Spectrum (cont.) The closer an orbital is to the nucleus, the more energy is required to move an electron in that orbital to a higher orbital. Thus, a jump from n=1 to n=2 requires more energy than a jump from n=2 to

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2/6/11 Rydberg Formula for Hydrogen The Rydberg formula for Hydrogen gives the difference in energy between two orbitals Note: R =1.097 x 10 m ¹ = Rydberg’s
2/6/11 0 2 4 6 8 10 12 14 16 Al Number of Electrons Energy (MJ/mol) PES measures the  energy to remove one  electron from  any   shell of a neutral  atom Notice how the  energies are grouped  based on the number  of electrons removed.

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