Ionic Bonds and Main Group Chemistry

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Ionic Bonds and Main Group Chemistry

• Chapter 6

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Ionization Energy

• The amount of energy required to remove the
  outermost electron form an isolated neutral atom
  in the gaseous state.

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Higher ionization energies

• Ionization energy always increases as you pull
  off more electrons.
• Ionization energies take a huge leap when we try
  to remove an electron from a new inner shell.

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Electron Affinity

• The energy change that occurs when an electron is
  added to an atom (or ion) in the gaseous state.
  Frequently costs nothing but actually yields
  energy therefore EAs are usually negative.

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Ionic Bonds

• Ions are held together by ionic attraction where
  the force of attraction is governed by Coulombs
  Law.
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•  
• Makes sense
• Large Z ? strong attraction ? larger E
• Large d ? charge felt less ? smaller E

Zion charge d distance between nuclei
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Lattice Energies
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Formation of ionic compounds

• Get elements as atoms (generally requires energy)
• Form ions (anions are energetically favorable,
  cations are unfavorable)
• Bring ions together (favorable)
• Condense to solid phase (favorable)

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Energetics of NaCl Formation

• Na(s) ??Na(g) 107.3 kJ/mol
• Na(g) ?? Na 1e? 495.8 kJ/mol
• 1/2 Cl2(g) ?? Cl (g) 122 kJ/mol
• Cl(g) ?? Cl?(g) ?348.6 kJ/mol
• Na(g) Cl?(g) ? NaCl(s) ?787 kJ/mol
• Na(s) 1/2 Cl2(g) ?? NaCl(s) ?411 kJ/mol

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• Determine the energy of formation of MgCl2 from
  the elements.

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magnesium bromide

• Mg(s) ?? Mg(g) 147.7 kJ/mol
• Mg(g) ?? Mg 1e? 737.7 kJ/mol
• Mg(g) ?? Mg2(g) 1e? 1450.7 kJ/mol
• Br2(g) ?? 2 Br (g) 193 kJ/mol
• 2Br(g) ?? 2Br?(g) 2(?325 kJ/mol)
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  ?650 kJ/mol
• Mg2(g) 2Br?(g) ? MgBr2(s) ?2440 kJ/mol
• Mg(s) Br2(g) ?? MgBr2(s) ? 561 kJ/mol

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• Calculate the energy released in kJ/mol in the
  reaction
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• Na(s) 1/2 I2(s) ?? NaI(s)
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• The energy of vaporization of Na(s) is 107
  kJ/mol. The sum of the
• enthalpies of dissociation and vaporization of
  I2(s) is 214 kJ/mol, and the lattice energy of
  NaI is 704 kJ/mol.

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• Calculate the energy released in kJ/mol when LiH
  is formed in the reaction
• Li(s) ½ H2(g) ? LiH(s)
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• Heat of vaporization, Li 161 kJ/mol
• Dissociation energy, H2 436 kJ/mol
• Lattice energy, LiH -917 kJ/mol
• Ionization energy, Li 520 kJ/mol
• Electron affinity, H -73 kJ/mol
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• Answer -91 kJ/mole net change

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Descriptive Chemistry

• Alkali Metals
• Alkaline Earths
• Aluminum
• Halogens
• Nobel Gases