CHEM 1A Lecture Notes - Lecture 9: Ab3, Trigonal Pyramidal Molecular Geometry, Ab4

• School: UC-Irvine
• Department: Chemistry
• Course: CHEM 1A
• Professor: Craig Martens

Document Summary

The octet rule applies mainly to second period elements, for other elements, many exceptions exist, due to: There are not enough valence electrons available in the structure to fill the octet on each atom. Octet rule is based on filling s and p shells (2+6=8 positions). Many atoms have d shells available and thus more positions to fill electrons. Some atoms lack the number of valence electrons to fill the shell. They form stable compounds with less than eight electrons surrounding them. Molecules with odd number of electrons cannot fulfill the octet rule for all the atoms. Elements beyond period 2 may have more orbitals available for allocating electrons. This often results in atoms surrounded by more than 8 electrons. ** for elements beyond the 2nd period: if a resonance structure can be formed that obeys the octet rule, then that structure can still be preferred even if it has greater formal charges.