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MOLECULAR STRUCTURES. Exceptions to the Octet Rule. A small group of molecules have an odd # of valence electrons (like NO 2 ) Some don’t have enough electrons to equal an octet (like BH 3 ) Some have more than 8 electrons and are referred to as having an expanded octet.
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Exceptions to the Octet Rule • A small group of molecules have an odd # of valence electrons (like NO2) • Some don’t have enough electrons to equal an octet (like BH3) • Some have more than 8 electrons and are referred to as having an expanded octet. • Example: SF6 and PCl5
VSEPR Model • Molecular Shapes are determined by the orbitals that overlap when electrons are shared. • The model that determines shape is called the Valence Shell Electron Pair Repulsion Model (VSEPR). • Electron repulsion causes atoms to be at specific angles to each other.