Electrons

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Electrons the early years
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Electromagnetic Radiation

• Radiant energy that travels through space at the
  speed of light in a vacuum.

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Wave particle duality
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Light as a wave

• Waves have 3 primary characteristics
• 1. Wavelength distance between two peaks in a
  wave.
• 2. Frequency number of waves per second that
  pass a given point in space.
• 3. Speed speed of light is 2.9979 ? 108 m/s.

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Wavelength and frequency are inversely
proportional

• ? ? c
• ? frequency s?1 hertz (Hz)
• ? wavelength (m)
• c speed of light (m/s)

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Light as a particlePhotoelectric Effect
The photoelectric effect occurs when photons of
sufficient energy actually kick electrons off of
the surface being struck by light.
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Light as a particleMax Planck
Transfer of energy is quantized, and can only
occur in discrete units, called quanta.
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Plancks Constant

• ?E change in energy, in J
• h Plancks constant, 6.626 ? 10?34 J s
• ? frequency, in s?1
• ? wavelength, in m

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Light as a particleEnergy and Mass (Einstein)

• E mc2
• E energy
• m mass
• c speed of light

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Particles as wavesDeBroglie

• Einstein Planck

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Particles as wavesDeBroglie

• Rearranging

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Particles as wavesDeBroglie

• For a generic particle (not EMR)

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deBroglies Equation

• ? wavelength, in m
• h Plancks constant, 6.626 ? 10?34 J s
• m mass, in kg
• ? velocity, in m/s

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Explaining the electron

• Continuous spectrum Contains all the
  wavelengths of light.
• Line spectrum Contains only some of the
  wavelengths of light.

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Explaining the electron

• When a sample of an elemental gas is electrified
  it emits electromagnetic radiation

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Explaining the electron

• When viewed through a diffraction grating, each
  element produces a distinctive line spectrum

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Hydrogens Line Spectrum(Balmer series visible)
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Hydrogens Line SpectrumUV, Visible, Infrared)
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The Bohr Model
The electron in a hydrogen atom moves around the
nucleus only in certain allowed circular orbits
(quantized energy states.)
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The Bohr Model
Orbits are determined by distance from nucleus
where orbit circumference is a whole number
multiple of the deBroglie wavelength.
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The Bohr Model
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How does Plancks Theory support Bohrs
quantized orbit

• The Hydrogen Electron Visualized as a Standing
  Wave Around the Nucleus

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The Bohr Model
The energy of the orbits increases with distance
from the nucleus. Ground State The lowest
possible energy state for an atom (n 1).
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The Bohr Model
An electron can absorb energy and jump from its
ground state to a higher energy orbit (excited
state).
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The Bohr Model
Electrons will not remain in an excited
state. Electrons emit energy in the form of
photons so that they can return to the ground
state. These photons make up the line spectrum.
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The Bohr Model
The frequency of the lines depends on the size of
the jump.
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The Bohr Model

• E energy of the levels in the H-atom
• z nuclear charge (for H, z 1)
• n an integer

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Energy Changes in the Hydrogen Atom

• ?E Efinal state ? Einitial state

• ?E -2.178x 10-18J 1/nf2 1/ni2

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Quantum Model
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Quantum Mechanics

• Based on the wave properties of the atom
• ? wave function
• mathematical operator
• E total energy of the atom
• A specific wave function is often called an
  orbital.

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Heisenberg Uncertainty Principle

• x position
• mv momentum
• h Plancks constant
• The more accurately we know a particles
  position, the less accurately we can know its
  momentum.

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Lets say you have a room with flies
flying around in it
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The flies are not just anywhere in the room. They
are inside boxes in the room.
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You know where the boxes are, and you know the
flies are inside the boxes, but
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you dont know exactly where the flies are inside
the boxes
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The room is an atom The flies are electrons The
boxes are orbitals
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The room is an atom The flies are electrons The
boxes are orbitals
Science has determined where the orbitals are
inside an atom, but it is never known precisely
where the electrons are inside the orbitals
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Hey, where am I?
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Probability Distribution

• square of the wave function (?2)
• probability of finding an electron at a given
  position

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Quantum Numbers (QN)

• 1. Principal QN
• (n 1, 2, 3, . . .) - related to size and
  energy of the orbital.
• Defines an energy level or shell

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Quantum Numbers (QN)

• 2. Angular Momentum QN
• (l 0 to n ? 1) - relates to shape of the
  orbital.
• n and l together define a sublevel or subshell

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• Letters are also used to represent the 2nd
  quantum number

l letter
0 s
1 p
2 d
3 f
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Quantum Numbers (QN)

• 3. Magnetic QN
• (ml l to ? l ) - relates to orientation of
  the orbital in space relative to other orbitals.

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Quantum Numbers (QN)

• 4. Electron Spin QN (ms ½ , ? ½) - relates
  to the spin states of the electrons.

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Pauli Exclusion Principle

• In a given atom, no two electrons can have the
  same set of four quantum numbers (n, l, ml , ms).
• Therefore, an orbital can hold only two
  electrons, and they must have opposite spins.

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So what are the sizes and shapes of orbitals?
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The area where an electron can be found, the
orbital, is defined mathematically, but we can
see it as a specific shape in 3-dimensional space
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z
y
x
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z
y
The 3 axes represent 3-dimensional space
x
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z
y
For this presentation, the nucleus of the atom is
at the center of the three axes.
x
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The 1s orbital is a sphere, centered around the
nucleus
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The 2s orbital is also a sphere.
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The 2s electrons have a higher energy than the
1s electrons. Therefore, the 2s electrons are
generally more distant from the nucleus, making
the 2s orbital larger than the 1s orbital.
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1s orbital
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2s orbital
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Dont forget an orbital is the shape of
the space where there is a high probability of
finding electrons
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Dont forget an orbital is the shape of
the space where there is a high probability of
finding electrons
The s orbitals are spheres
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There are three 2p orbitals
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The three 2p orbitals are oriented perpendicular t
o each other
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z
This is one 2p orbital (2py)
y
x
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z
another 2p orbital (2px)
y
x
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z
the third 2p orbital (2pz)
y
x
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Dont forget an orbital is the shape of
the space where there is a high probability of
finding electrons
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Dont forget an orbital is the shape of
the space where there is a high probability of
finding electrons
This is the shape of p orbitals
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z
y
x
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z
2px
y
x
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z
2px and 2pz
y
x
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z
The three 2p orbitals, 2px, 2py, 2pz
y
x
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once the 1s orbital is filled,
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the 2s orbital begins to fill
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once the 2s orbital is filled,
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the 2p orbitals begin to fill
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each 2p orbital intersects the 2s orbital and the
1s orbital
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each 2p orbital gets one electron before pairing
begins
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once each 2p orbital is filled with a pair of
electrons, then
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the 3s orbital gets the next two electrons
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the 3s electrons have a higher energy than 1s,
2s, or 2p electrons,
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so 3s electrons are generally found further from
the nucleus than 1s, 2s, or 2p electrons
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D orbitals
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f orbitals