Modern Atomic Theory Review

• ^^light is a form of electromagnetic radiation^^

  • properties of both waves and particles:
  • wavelength (λ) - the distance between adjacent wave crests, meters
    • red light (750 NM) has longest wave length
    • violet light (400 NM) has shortest wave length
    • ==1 NM = 1 * 10^-9 meters==
  • frequency (v) - number of cycles or crests that pass through a stationary point in one second
  • amplitude - the height of the wave from zero to crest
  • ^^wavelength and frequency are inversely/indirectly related^^ - the shorter the wavelength, the higher the frequency

  

  • ==speed of light====: 2.998 * 10^8 meters/second = λv==

• electromagnetic radiation

  • light can be viewed as a stream of particles
  • particle of light is a ^^photon^^
  • photon - a single packet of light energy
    • has specific wavelength, determines what light we see
    • wavelengths of spectral lines are characteristics of the element
    • make up atomic emission spectra
    • no two elements have the same emission spectra
  • amount of energy carried in the packet depends on the wavelength of the light - ^^the shorter the wavelength, the greater the energy^^
    • light waves that carry more energy in their crests are closer
    • violet light carries more energy per photon than red light
  • the photoelectric effect - the emission of electrons from a metal when light shines on the metal
  • ^^quantum of energy^^ - the minimum quantum of energy that can be lost or gained by an atom
  • ^^quantized^^: an electron has to absorb/emit a specific amount of energy to move from one energy level to another
    • ^^ground state^^: the normal energy level any given electron occupies
    • ^^excited state^^: the energy level an electron occupies when it has absorbed the specific quantum of energy to move up to that level
  • %%Planck’s Law%% - ==E=Hv==
    • E - energy, joules
    • H - ==Planck’s constant, 6.626 * 10^-34 J*S==
    • v - frequency

• %%Bohr’s Model%%

  • Niels Bohr changed Rutherford’s model to include newer discoveries about how the energy of an atom changes when the atom absorbs/emits energy
  • proposed electron is found only in specific circular paths/orbits around the nucleus ❌
    • incorrect - if the orbits were truly circular, the electron would spiral into the nucleus
  • each possible electron orbit has a fixed energy - ^^energy level^^ ✅
  • each orbit is a specific distance from the nucleus and at each specific energy
    • ^^impossible for an electron to exist between orbits^^
  • ^^amount of energy is directly related to the frequency → wavelength^^

• %%de Broglie%%: proposed “electrons be considered as waves confined to the space around an atomic nucleus”

• %%Heisenberg Uncertainty Principle%%

  • Werner Heisenberg
  • states that it is impossible to determine simultaneously both the position and velocity of an electron
  • “we cannot know both the position and speed of a particle, such as a photon or electron, with perfect accuracy”
  • %%Schrödinger Wave Equation%%
    • Erwin Schrödinger developed an equation that treated electrons as waves
    • ^^Quantum Theory^^ - describes mathematically the wave properties of electrons
    • electrons exist in certain regions called orbitals
    • orbitals - 3D regions around the nucleus that indicate the probable location of an electron
      • represent probability maps showing a statistical attribution of where the electron is likely to be found
    • 4 Wave Properties
    • ^^Energy Level^^: Principal Quantum Numbers - number specifying the principle shell of orbital
      • n - indicates the energy level
      • energy increases with principal quantum number
      • maximum of 7 energy levels
      • ==n^2== - how many orbitals in any energy level
      • ==2n^2== - maxim. number of electrons possible in any energy level
    • ^^Sub Level^^: Shapes of Quantum Mechanical Orbitals
      • letter indicates subshell of orbital, specifies shape
      • possible letters - s, p, d, f
      • electrons are more likely to be found closer to the nucleus than farther away
    • ^^Orbital^^: Orientation
      • s - 1 orbital
      • p - 3 orbitals
      • d - 5 orbitals
      • f - 7 orbitals
    • ^^Spin^^: clockwise or counterclockwise

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• Electron Configuration

  • arrangement of electrons in an atom and the way in which the electrons are arranged in various orbitals around the nucleus
  • %%Aufbau Principle%%
  • the electrons will fill the orbitals in a very specific order
  • lowest → highest energy
  • ^^The Diagonal Rule^^

  

  • %%Pauli Exclusion Principle%%
  • an individual orbital may describe at most TWO electrons
  • in order to occupy the orbital, the two electrons must have opposite spins: ⬆⬇
  • EXAMPLES
  • Carbon 6e- : 1s^2, 2s^2, 2p^2
  • Aluminum 13e- : 1s^2, 2s^2, 2p^6, 3s^2, 3p^1
  • Noble Gas Configuration
  • Aluminum 13e- : [Ne] 3s^2, 3p^1

• %%Hund’s Rule%%

  • orbitals in the same sub-level must all fill with one electron before a second electron is added to any of the orbitals: (n)p^4 - ⬆⬇ ⬆ ⬆

  • the “single” electrons will all have the same spin direction

  • Orbital Diagram

    

• @@Valence@@ and Core Electrons

  • valence electrons are the electrons on the outermost energy level
  • the noble gases always have full valence shells
  • Selenium 34e- : 1s^2, 2s^2, 2p^6, 3s^2, 3p^6, 3d^10, @@4s^2@@, 3d^10, @@4p^4@@
  • Silicon 14e- : 1s^2, 2s^2, 2p^6, @@3s^2, 3p^2@@
  • the chemical properties of elements are largely determined by the number of valence electrons they contain
  • properties vary in a periodic fashion because the number of valence electrons is periodic

• Atomic Physical Properties

  • Atomic Size ⬇⬅
  • left-right ^^decreases ⬅^^
    • across a period, the amount of protons in the nucleus increases which has a stronger pull on the electrons, causing them to move closer to the nucleus
  • top-bottom ^^increases ⬇^^
    • size of the orbital increases with increasing principal quantum shell number
    • electrons occupying the outermost orbitals are farthest from nucleus
  • Ionization Energy ⬆➡
  • amount of energy needed to remove a single electron
  • left-right ^^increases ➡^^
    • electrical pull on electrons from the # protons in nucleus causes increases amount of energy needed
  • top-bottom ^^decreases ⬆^^
    • electrons in outermost orbitals are less affected by the electrical pull from nucleus
  • Electronegativity ⬆➡
  • ability of an atom of an element to attract electrons when the atom is in a compound
  • left-right ^^increases ➡^^
  • top-bottom ^^decreases ⬆^^

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