Periodic Trends

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Periodic Trends

• Chem 441 Inorganic Chemistry
• Dr. Jeff Seyler

2
Electron Configuration

• based on H-orbitals (Schrödinger wave function)
• contraction of orbitals as Z increases
• PT rows relate to n QN (energy level)
• (n-1)d and (n-2)f
• PT l-blocks, columns
• number of columns depend on max number of
  electrons
• exceptions to Aufbau principle
• Cr Ar4s13d5, DEn and Hunds rule
• valence electrons, control reactivity
• highest n and partially filled (n-1)d electrons

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Electron Shielding

• Core electrons shield valence electrons
• Valence electrons exchanged/shared in reactions
• s-orbital electrons shield more effectively
• Due to penetration (see radial distribution
  plots)
• Zeff (effective nuclear charge)
• Slaters rules offer quick approximation
• Zeff increases across a PT row
• Additional protons, same level (n QN)

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Ionization Energy

• energy required to remove an electron
• M (g) energy ? M(g) e-
• decreases as n QN increases
• easier to remove e- as distance from nucleus
  increases
• increases from left to right across a row
• Zeff increase outweighs shielding for given l
• deviations from trends
• stability for half-full and full sublevels

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Electron Affinity

• energy associated with gain of electron
• M (g) e- ? M-1 (g), (- DH), historical
• M-1 (g) ? M (g) e- (DH), Miessler text
• endotherms and exotherms
• most elements have DH
• generally, nonmetals favor gain of electron
• trends in EA
• similar to IE, offset one atomic number
• deviations from trends
• stability for half-full and full sublevels

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Atomic Radii

• Determined from crystal data
• atomic, ionic, and covalent radii
• Depends on n QN
• size increases down column
• Depends on Zeff
• size decreases left to right
• Deviations from trends
• Lanthanide contraction

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Ionic Radii

• cations
• radius decrease with increasing charge
• anions
• radius increase with increasing - charge
• values in pm

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Electronegativity

• power of an electron to attract electrons to
  itself in a covalent bond
• Pauling (1930s) used BDE (eV units)
• Mulliken used avg of IE and EA
• Allen used energy of valence shell electrons
• Jaffe determined orbital electronegativities
• trends
• increase left to right
• decrease down a column

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figures
The following slides contain figures linked
within the presentation.
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Z and Radial Distribution
rmax radial distribution decreases as Z increases
for a given energy level, n (size decreases from
left to right across a row)
H 3p
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Periodic Table l-blocks
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Aufbau exceptions
V - 4s23d3 to Cr - 4s13d5 Ni - 4s23d8 to Cu -
4s13d10
3d
4s
Fe to Zn, the 4s electrons are highest energy (3d
drops lower than 4s with increasing charge)
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Orbital Penetration
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Ionization Energies
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IE1 Trends
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IE Trends
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Electron Affinities
- DH
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Electron Affinities cont.
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Transition Metal radii
Lanthanide contraction 5d row same size as 4d
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Pauling Electronegativities
2.1 (H)
4.0
0.7
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