The octet rule states that atoms tend to bond in such a way that each atom has eight electrons in its valence shell, achieving a stable electronic configuration similar to that of noble gases. Let’s analyze each molecule individually:
- PF5 (Phosphorus Pentafluoride): This molecule does not satisfy the octet rule. Phosphorus has 5 valence electrons and can accommodate more than 8 electrons in its valence shell due to its position in period 3 of the periodic table. In PF5, phosphorus forms five bonds, utilizing all its valence electrons plus some d orbital participation, leading to a total of 10 electrons.
- CS2 (Carbon Disulfide): This molecule does satisfy the octet rule. Carbon has 4 valence electrons and forms two double bonds with sulfur, which has 6 valence electrons. Each atom in CS2 achieves an octet through bonding: carbon shares its 4 electrons and each sulfur atom shares 2 electrons, resulting in 8 total electrons around each atom.
- BrF3 (Bromine Trifluoride): This molecule does not satisfy the octet rule. Bromine can expand its octet due to its position in period 4. In BrF3, bromine forms three bonds and has two lone pairs of electrons, leading to a total of 10 electrons around bromine.
- CO32- (Carbonate Ion): This molecule does satisfy the octet rule. The carbon atom has 4 valence electrons and forms a bond with three oxygen atoms, one of which has a double bond while the others carry a single bond and a -1 charge. This arrangement allows the carbon atom to have a total of 8 electrons through sharing, leading to stable electronic configuration.
In summary:
- PF5: Does not satisfy the octet rule
- CS2: Satisfies the octet rule
- BrF3: Does not satisfy the octet rule
- CO32-: Satisfies the octet rule