Arrangement of Electrons in Atoms

1
Arrangement of Electrons in Atoms

• Chapter 4

2
The New Atomic Model

• Investigations ? relationship between light and
  atoms electrons
• How are electrons arranged? Why dont they fall
  into the nucleus?

3
Light a wave or particle?

• Wave Description
• Electromagnetic Radiation energy that acts like
  a wave in space
• All forms create Electromagnetic Spectrum

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Electromagnetic Spectrum
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Electromagnetic Spectrum

• All forms move at speed of light, c, 3.00x108 m/s
• Forms identified by
• wavelength, ?, the distance b/ corresponding
  points on adjacent waves. Units nm, cm, or m
• Frequency, ?, of waves that pass a given point
  in a specific time, 1 sec. Unit 1/s Hertz, Hz

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Wavelength and Frequency
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Wavelength and Frequency

• c ??
• Inverse proportion equation!!

Frequency, 1/s
speed of light, m/s
wavelength, m
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Calculation

• Calculate the wavelength of a radio wave with a
  frequency of 102.7 x 106s-1
• Determine the frequency of light whose wavelength
  is 5.267 nm.

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Particle Nature of Light

• Photoelectric Effect emission of electrons from
  a metal when light shines on the metal

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Photoelectric Effect

• Light had to be certain frequency to knock e-
  loose
• Wave theory ? any frequency should work (just
  might take a while)
• Light must also be a particle!
• Max Planck(1900) explanation objects emit energy
  in small packets called quanta
• Video - 16

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Max Planck

• Quantum of energy is the smallest amount of
  energy that can be lost or gained by an atom
• E h?

Frequency, s-1
Energy of quantum, in joules, J
Plancks constant, 6.626x10-34 Js
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Energy Calculation

• What is the energy of green light, with a
  wavelength of 500. nm?

13
Albert Einstein

• Light is both wave and particle!
• Particle of light photon, having zero mass and
  a quantum of energy
• Photons hit metal and knock e- out, but photon
  has to have enough energy

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H-atom Emission Spectrum

• Pass a current through gas at low pressure it
  excites the atoms
• Ground state lowest energy state of an atom
• Excited state atom has higher potential energy
  than it has in ground state

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H Atom Spectrum

• When atom jumps from excited state to ground
  state it gives off energy ? LIGHT!

E2
Ephoton E2 E1 hv
E1
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Bohr Model of H-atom
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H-atom Line Emission Spectrum
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Element Emission Spectras
Helium 23 lines
Neon 75 lines
Argon - 159 lines
Xenon 139 lines
Mercury 40 lines
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H-atom Line Emission Spectrum

• More lines in UV (Lyman series) and IR(Paschen
  series)
• Why did H-atom only emit certain colors of light?
• Explanation led to new atomic theory ? Quantum
  Theory

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Bohr Model of H-atom

• 1913 Niels Bohr
• e- circles nucleus in certain paths, orbits or
  atomic energy levels
• e- is higher in energy the farther away from
  nucleus
• e- cannot be between orbits
• Video - 23

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Bohr Model of H-atom
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Bohr Model of H-atom

• From wavelengths of emission spectrum Bohr
  calculated energy levels of H-atom
• Model worked ONLY for H-atom

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Quantum Model of Atom

• Can e- behave as a wave?
• Yes!
• To find e- use a photon, but photon will knock
  the e- off course
• Heisenberg Uncertainty Principle impossible to
  determine position and velocity of a particle at
  the same time.

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Schrödinger Wave Equation

• 1926 developed equation and only e- waves of
  certain frequencies were solutions
• Quantization of e- ? probability of finding e- in
  atom
• No neat orbits ? probability clouds or orbitals

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Electron Configurations
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Atomic Orbitals

• Def 3-D region around nucleus that indicates the
  probable location of an electron
• Energy levels or shells
• Numbered 1-7
• Smaller number closer to nucleus, lower energy

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Sublevels

• Each shell has sublevels
• s
• 1 s orbital
• p
• 3 p orbitals
• d
• 5 d orbitals
• f
• 7 f orbitals

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Shells and Sublevels

• Shells and sublevels together
• 1s
• 2s, 2p
• 3s, 3p, 3d
• 4s, 4p, 4d, 4f, etc.
• s is the lowest energy and f is the highest

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Orbitals

• Each orbital in a sublevel can hold a maximum of
  2 e-
• 1 s 2 e- max.
• 3 p orbitals 6 e- max.
• 5 d orbitals 10 e- max.
• 7 f orbitals 14 e- max.

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Electron Configurations

• Arrangement of e- in atom
• Orbital Notation
• H has 1e-
• Rules
• Aufbau Principle electron occupies lowest energy
  level that can receive it

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Electron Configurations

• 2. Pauli Exclusion Principle no two e- in an
  sublevel orbital can have the same spin
• 3. Hunds Rule orbitals of equal energy are
  occupied by one e- before pairing up e-. All
  single occupied orbitals must have same spin.
• He 2e-

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Energy of sublevels
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Electron Configurations

• N
• S
• Ti
• I

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Electron Configuration Notation

• B
• Ni
• Hg

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Noble Gas Notation

• Use noble gas from previous row
• Al
• Pb

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Special Cases

• d sublevel more stable with half-filled or
  completely filled sublevel
• Cr
• Cu