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

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 ⬆^^