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Formal Charge and Bond Energy

Formal Charge and Bond Energy. Definition. Each atom in a molecule can be thought of as having a Formal Charge Formal Charge = difference between the number of valence electrons on the free atom minus number of valence electrons assigned to the atom in the molecule.

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Formal Charge and Bond Energy

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  1. Formal Charge and Bond Energy

  2. Definition • Each atom in a molecule can be thought of as having a Formal Charge • Formal Charge = difference between the number of valence electrons on the free atom minus number of valence electrons assigned to the atom in the molecule

  3. Find the Formal Charge On Each Atom in the Structure below:

  4. Find the Formal Charge On Each Atom in the Structure below:

  5. Evaluating Lewis Structures • Atoms in molecules try to achieve formal charges as close to zero as possible • Example: Based on the two Lewis structures for sulfate, which is the best representation for the molecule?

  6. Bond Energy • Energy, in kJ, required to break a bond in 1 mole of a compound • Bond energies given in Table 8.4 (pg. 374)

  7. Enthalpy (H) • Bond energies can be used to calculate an approximate energy of reaction • H can be thought of as the energies required to break old bonds plus the energies released when new bonds are formed H = D(bonds broken) - D(bonds formed)

  8. Example • Use bond energies to calculate the H for the reaction of methane with chlorine and fluorine to give freon (CF2Cl2) CH4 + 2Cl2 + 2F2 CF2Cl2 + 2HF + 2HCl

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