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Formal Charge is discussed in Zumdahl, Pg380. Using the rules to determine Lewis Dot Structures, there are some compounds or ions that could have more than one viable Lewis Dot Structure (not talking about Resonance structures. It usually occurs when you have elements that can exceed the Octet Rule and are the central atom. There can not be two viable Lewis Dot Structure for a compound/ion, therefore there must be a way to determine which structure is more correct. There is and it is called FORMAL CHARGE. Formal charge - the difference between the number of valence electrons on free atom and number of valence electrons assigned to the atom in a molecule (valence e- shared - valence assigned) *lone pairs belong entirely to the atom in question *shared pairs are divided equally *atoms try to achieve formal charges as close to zero as possible *negative formal charges go to the most electronegative element involved in the bond *the sum of all the formal charges on an ion or molecule equal the overall charge on the species *formal charges are only estimates - not actual charges - actual charges are determined experimentally Example: Pg381 in Zumdahl (the species in question is the sulfate ion) |
Using the rules to determine Lewis Dot Structures, there are some compounds or ions that could have more than one viable Lewis Dot Structure (not talking about Resonance structures.
It usually occurs when you have elements that can exceed the Octet Rule and are the central atom.
There can not be two viable Lewis Dot Structure for a compound/ion, therefore there must be a way to determine which structure is more correct. There is and it is called FORMAL CHARGE.
Formal charge - the difference between the number of valence electrons on free atom and number of valence electrons assigned to the atom in a molecule (valence e- shared - valence assigned)