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C, N, O, and F always obey octet rule . H, Be do not follow octet rule Example: BeCl 2 , H 2 . If only 3 electron groups around central atoms, then central atom forms incomplete octet Example: BH 3. Group III (13) elements such as B, Al . Identify central atom and ligands.
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C, N, O, and F always obey octet rule H, Be do not follow octet rule Example: BeCl2, H2 If only 3 electron groups around central atoms, then central atom forms incomplete octet Example: BH3 Group III (13) elements such as B, Al Identify central atom and ligands If there are 4 electron groups around the central atoms, then the central atoms follows octet rule and appropriate formal charges: Example: BH4- The central atom should have a complete octet or expanded octet, therefore form as many multiple bonds as needed to achieve complete octets and multiple bonds as needed to reduce formal charges. Examples: TeO2, PO43- , XeO2F2 Third row elements (S, P, Cl etc) and greater atomic numbers