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The Quantum Model of an Atom - PowerPoint PPT PresentationTRANSCRIPT
Quantum Mechanical Model of the Atom
BC High ChemistryMr. Olejnik
Review of Atomic Models• Bohr’s Model– Electrons move in definate orbits or
energy levels around the nucleus
Wave model of atom• Modern model of atom– According to theory of
wave mechanics electrons don’t orbit nucleus predictably
– Impossible to determine location of electron, we interpret it with a “cloud”.
Light as Waves• Wavelength = distance between the
crests of two subsequent waves (wave = λ “lambda”)
• Frequency = how often a wave crosses a fixed point (v)
Think1. Which of the following has the
longest wavelength (λ)2. Which of the following has the
highest frequency (v)
Speed of Light• Speed of light ≈ 3.00 x 108 m/s = C
• C = λv– Λ & v are inversely proportional so if λ increases, v
decreases etc.
Quantum Mechanical Model• Mathematical Model of the atom based on
the Quantum Theory, • Quantum Theory basically says:–Matter has properties associated with waves.– Impossible to predict the exact position of e-– E- have both properties of particles & waves
Quantum Mechanical Model• Developed in the 1920’s• Werner Heisenberg (Uncertainty
Principle)• Louis de Broglie (electron has wave
properties)• Erwin Schrodinger (mathematical
equations using probability, quantum numbers)
Werner Heisenberg: Uncertainty Principle
• We can not know both the position and momentum of a particle at a given time.
Louis de Broglie, (France, 1892-1987)
Wave Properties of Matter (1923)•Since light waves have a particle behavior (as shown by Einstein in the Photoelectric Effect), then particles could have a wave behavior.•de Broglie wavelength h
mv
Particle vs. Wave• Is light particles or waves?– YES!
Erwin Schrodinger, 1925
• Quantum (wave) Mechanical Model of the Atom– Complicated equation used to
estimate an e-’s location– 4 quantum numbers describe
the location of e- in an atom
Yikes! You DON’T need to know this!
Quantum Model of Atom• Quantum model of atom:– Pattern of e- arrangement in an atom, described by quantum
numbers.
• Quantum Numbers:– 4 numbers that describe the properties and position of an e-.
• Orbital:– A region in space in which there is high probability of finding an
electron.
Four Quantum Numbers• Principal Quantum Number = “n”– Main energy level of an e-
• Angular Momentum Number = “l”– Indicates shape
• Magnetic Quantum Number = “m”– Indicates oreintation
• Spin Quantum Number = “spin”– Indicates direction e- is spinning
Principal Quantum Number: “n”
• Indicates main energy levels– n = 1, 2, 3, 4…
Angular Momentum Number, “ℓ”
• Indicates shape of orbital sublevels
• ℓ = n-1
ℓ sublevel0 s1 p2 d3 f4 g Elements in specific regions of the
periodic table have similar shapes.
Orbital Shapes
Magnetic Quantum Number, ml
• Indicates the orientation of the orbital in space.– Basically which spot it occupies.
– Values of ml : integers -l to l
• The number of values represents the number of orbitals possible.
• Example: if n = 3, l= 2, ml = -2, -1, 0, +1, +2
so ml could be in any of these spaces:
___ ___ ___ ___ ___ -2, -1, 0, +1, +2
Which sublevel does this represent?Answer: d
Magnetic Quantum Number, ml
Electron Spin Quantum Number, (ms or s)
• Indicates the spin of the electron (clockwise or counterclockwise).
• Values of ms: +1/2, -1/2
Example 1:• Fill out this chart for the following
quantum numbers: (3, 2, -1, -1/2)
Example 2:
• List the values of the four quantum numbers for orbitals in the 3d sublevel.
• Answer: – n=3
– l = 2
– ml = -2,-1, 0, +1, +2
– ms = +1/2, -1/2 for each pair of electrons