CHEM 11H Lecture Notes - Lecture 21: Benzene, Electronegativity, Phosphorus Pentafluoride

• School: Santa Clara University
• Department: Chemistry and Biochemistry
• Course: CHEM 11H
• Professor: Tan

Document Summary

Not a real charge, just used to help predict dominant lewis structure where more than 1 is possible. Lone pairs belong entirely to the atom. Shared e- divided equally between 2 sharing atoms. Formal charge (fc) = (# val e-) - ( * # bonding e-) - ( * # nonbonding e-) Sum of fcs must be same as overall ion charge. Negative fcs preferable on more electronegative atoms. Sometimes more than 1 valid lewis structure is possible. Actual structure resonance hybrid (average of the 3 structures) Other examples: ozone (o3) and benzene (c6h6) Lewis model: electrons assumed to be localized around pairs of atoms in reality, e- are more delocalized (which stabilizes e-), so resonance is needed to compensate for localized e- assumption. Bf3 reactive towards electron rich molecules like nh3. Only in elements period 3 and beyond. If there is a choice, place extra e- on the central atom, eg: i3.