7 - Electron Configurations and the Periodic Table

7 - Electron Configurations and the Periodic Table -...

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Chapter 7: Electron Configurations and the Periodic Table Explanations of periodic trends in physical and chemical properties are based on electron configurations – arrangements of electrons within atoms 7.1 Electromagnetic Radiation and Matter Excited – atoms gain energy when electrons absorb light and then release it in form of electromagnetic radiation (some is visible) Electromagnetic radiation consists of oscillating perpendicular electric and magnetic fields that travel through space at the same rate (“speed of light”); can be described in terms of frequency ( v ) or wavelength (λ) Spectrum is distribution of intensities of wavelengths or frequencies of electromagnetic radiation emitted or absorbed by an object Visible light is a very small part of the entire spectrum Radiation’s energy increases from the radio wave end of spectrum (low frequency, long wavelength) to gamma ray end (high frequency, short wavelength) Wavelength is distance between adjacent crests (or troughs) in a wave Frequency is number of complete waves passing a point in a given period of time (cycles per second, per second 1/s = s -1 = Hz) Amplitude is the height of the wave crest and accounts for intensity (brightness) of radiation Frequency of electromagnetic radiation is related to wavelength by v λ = c, c is speed of light 7.2 Planck’s Quantum Theory When an atom in a hot object emits radiation, it does so only in packets (quantum ) having a minimum amount of energy; quantum is the smallest possible unit of a distinct quantity Quantum theory – E quantum = h v radiation ; h = Planck’s constant = 6.626 x 10 -34 Js and relates frequency of radiation to its energy per quantum As temperature increases, the maximum intensity of emitted light shifts from red to yellow to blue E = hc / λ the energy per quantum of radiation increase as the wavelength gets shorter The Photoelectric Effect o Photoelectric effect – metals emit electrons when illuminated by light of certain wavelengths; for each photosensitive metal, there is a threshold wavelength below which no photoelectric effect is observed o Einstein proposed that Planck’s quanta are massless “particles” of light called photons light was a stream of particles that had particle-like and wave-like properties o Each photon has energy equal to hv so only photons with E greater than E min will have enough energy to knock an electron loose; photons with less energy do not have enough energy to remove electrons explains why only certain wavelengths of light can eject electrons from certain metals o Intensity of radiation is proportional to number of photons, total energy is proportional to number of photons times energy per photon higher intensity light source causes higher photoelectric current o Visible light and electromagnetic radiation have wave and particle characteristics dual nature of light o Refraction is bending of light as it crosses the boundary from one medium to another
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7 - Electron Configurations and the Periodic Table -...

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