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Electromagnetic Radiation Notes

  • Electromagnetic radiation
    • all types of light - visible and nonvisible
  • speed of light © - 3.00 x 10^8 m/s
  • Properties of waves
    • wavelength
      • units, meters, and nanometers
    • red light - longest wavelength (750 nm)
    • violet light - shortest wavelength (400nm)
  • crest is the top of the wave
  • trough is the bottom of the wave
  • we believe that electrons behave like photons
  • frequency (v)
    • units - Hertz (Hz) or 1/s of s^-1
    • the number of waves that pass a given point in a unit of time
  • velocity (speed of light)
    • c = wavelength * frequency
    • c = speed of light = 3.00 x 10^8 m/s
    • frequency and wavelength inversely proportional
  • Problems
  • What is the wavelength of radiation with a frequency of 2.25 x 10^14 Hz?
  • 3.00 x 10^8 m/s = x * 2.25 x 10^14 1/s
  • x = 1.33 x 10^06 m
  • What is the frequency of radiation with a wavelength of 3.75 x 10^-7 m?
  • 3.00 x 10^8 m/s= 3.75 x 10^-7m * x 1/s
  • x = 8.00 x 10^14 1/s
  • What is the frequency of radiation with a wavelength of 631 nm?
  • 3.00 x 10^8 m/s = 6.31 x 10^-7 m * x
  • x = 4.75 x 10^14 1/s
  • Albert Einstein
    • light behaved as particles
    • photons
      • particle of light
      • packet of energy
      • depends upon the wavelength of the light
        • Short wavelengths, greater the energy
    • Which type of visible light has the greatest amount of energy?
    • violet - it has the shortest wavelength and it has the highest frequency
    • Which type of visible light has the least amount of energy?
    • red - it has the longest wavelength and it has the lowest frequency
  • Electromagnetic Radiation
    • electromagnetic radiation
    • all types of light - same speed
    • wavelengths from 10^-16m to 10^6 m
    • energy per photon; greater with short wavelength
  • gamma ways - smallest wavelengths
  • x-rays - pass through many substances
  • UV light - sunlight; sunburn
  • visible light - violet to red
  • infrared light - longer wavelengths; less energy per photon; heat
  • microwaves - used for radar and microwaves
  • radio waves - transmit signals for AM and FM radio
  • Bohr Model
    • continuous spectrum
    • when you shine a white light through a prism
    • emission spectrum (bright line spectrum)
    • unique to each element
    • a few bands of color to identify bands of color to identify that element
    • heat up the electrons of an element and then they give off light
  • Niels Bohr
  • electrons travel in a circular orbit
  • electrons in specific, fixed distances from the nucleus
  • quantized (quantum)
  • more energy further away from the nucleus
  • certain amount of energy needed to move to the next energy level
  • excited state
  • electrons emit a photon when returning
  • ground state
  • all electrons in lowest possible energy level
  • smaller wavelength; greater energy
  • only worked for hydrogen
    • Max Planck
    • electrons and photons behaved like particles
    • quantum
    • Ephoton = hv
    • h = 6.63 x 10^-34 Js
  • Problems
  • What is the energy of radiation that has a frequency of 6.79 x 10^14 Hz?
  • E = 6.79 x 10^14 J*s * 6.63 x 10^-34 1/s
  • E = 4.50 x 10^-19 J
  • What is the wavelength of radiation that has an energy of 8.98 x 10^-19J?
  • 8.98 x 10^-19J = 6.63 x 10*-37 Js * frequency
  • frequency = 1.354 x 10^15 1/s
  • 3.00 x 10^8 m/s = 1.354 x 10^15 1/s * wavelength
  • wavelength = 2.22 x 10^-7 m
  • What is the energy of radiation that has a wavelength of 245nm?
  • 3.00 x 10^8 m/s = 2.45 x 10-7 m * frequency
  • frequency = 1.224 x 10^15 1/s
  • E = 6.63 x 10^-34 Js * 1.224 x 10^15 1/s
  • E = 8.12 x 10^-19 J
  • Quantum Mechanical Model
    • quantum mechanical model
    • probability of where the electron is found
    • not an orbital path; does not represent the exact path
    • also called the electron cloud model
    • as your go further out, the density of electrons decreases and so your odds of finding an electron decrease
  • Quantum Mechanical Orbitals
    • quantum numbers
    • principal quantum number (n)
    • represents an energy level - we have seven on earth (they are the periods on the periodic table)
    • sublevel (l)
      • four sublevels on periodic table
      • s, p, d, and f
  • n tells you which level you are in which is equal to the number of sublevels
  • n=1; 1s
  • n=2; 2s, 2p
  • n=3; 3s, 3p, 3d
  • n=4; 4s, 4p, 4d, 4f
  • First two columns are the s sublevel
  • 2-12 are the d sublevel
  • last six are d, excluding helium
  • bottom two rows are f
  • n=5; 5s, 5p, 5d, 5f, 5g
  • n=6; 6s, 6p, 6d, 6f, 6g, 6h
  • orbitals(m)
    • region of space within a sublevel
    • only 2 electrons fit in each orbital
    • s orbital - spherical shape
    • p orbital - figure eight/dumbbell
  • electron spin (m)
    • 2 electrons fit in each orbital
      • opposite spins
  • s - 1 orbital - 2 electrons
  • p - 3 orbitals - 6 electrons
  • d - 5 orbitals - 10 electrons
  • f - 7 orbitals - 14 electrons
  • n - represents energy levels
  • n^2 - number of orbitals in an energy level
  • 2n^2 - number of electrons in an energy level
    • Electron configuration represents the location of an electron using the energy level, sublevel, and the number of electrons in the sublevel
    • 1s^1 (1st energy level, s sublevel, one electron)
    • Orbital diagrams use arrows to represent electrons and their orbitals
  • Pauli exclusion principle
    • no two electrons can have the same set of quantum numbers
    • no two electrons in the same orbital can have the same spin
    • Hund's rule
    • when filling orbitals of the same energy, fill each orbital with one electron first then pair the electrons
    • the maximum number of unpaired electrons is the lowest energy
  • overlapping starts on energy level three and four
  • Electron Configurations with the Periodic Table
  • valence electrons
  • outermost s or s and p
  • How many valence electrons are the in the following atoms:
  • N - 5
  • Fe - 2
  • Ge - 4
  • Br - 7
  • Pattern
    • Group 1A - alkali metals - ns1
    • Group 2A - alkaline earth metals - ns2
    • Group 3A (13) - ns2np1
    • transiition metals - d block
    • lanthanides and actinides - f block
    • exceptions in group 6 and group 11
    • Cr - Ar4s13d5
    • Electron Configurations of Ions
    • K+
    • K = Ar4s1
    • K+ = Ar = Ne3s23p6
    • Ca2+
    • Ca - Ar4s2
    • Ca2+ = Ne3s23p6
    • N3-
    • N - 1s22s22p6
    • Cl-
    • Cl - Ne3s23p6
    • Fe3+ = Ar3d5
    • Cu2+
    • Cu - Ar4s13d10
    • Cu2+ = Ar3d9
  • Periodic Trends
    • Atomic size
    • size of the atom
    • neutral atom - same number of protons and electrons
    • two atoms bonded to each other - measure distance from one nucleus to the other
    • Group trend
  • start at the top of the table and go down
  • the atomic size gets bigger as you go down a group
  • added on filled energy levels
  • shielding effect
  • the repulsion between the inner and outer electrons - makes it bigger
  • Nuclear charge
  • attraction of the electrons to the protons in the atom
    • protons
  • distance
  • As you get further away, the attraction decreases
  • Periodic trend
  • usually left to right
  • size decreases going across the periodic table
  • add one more proton and electron
  • stronger attraction which makes it smaller
  • shielding effect remains constant - only time it goes into effect is when you go down
  • Ionic Size
    • ion has a charge
    • cation - +
    • anion - -
    • Trends in ion size
    • cations
    • decrease in size (remove electron)
    • more protons than electrons (increase in attraction)
    • greater attraction
    • anions
    • increase in size
    • proton to electron ratio is lower
    • Group trends
      • increases down a group
      • adding energy levels
      • shielding effect
  • Ionization Energy
  • the energy required to remove an electron from a gaseous atom
  • Na(g) → Na+ + 1e-
  • F(g) → F+ + 1e-
  • Group trends
    • decreases as you down a group
    • adding energy level
    • electrons further out
    • Periodic trends
    • increases as go across
    • shielding effect remains constant - same energy level
    • Periodic Table - Metals/Nonmetals
    • metals tend to lose electrons
    • nonmetals tend to gain electrons

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