In which of the following compounds is the central atom's octet expanded to include 12 electrons?

• A. PF6-
• B. SF6
• C. XeF4
• D. PCl5

Answer: (A)

Verified step by step guidance

1. Recall the octet rule, which states that atoms tend to have eight electrons in their valence shell to achieve stability. However, elements in period 3 or beyond can have expanded octets due to available d orbitals.
2. Identify the central atom in each compound and determine its period in the periodic table. Elements from period 3 or higher can expand their octet beyond 8 electrons.
3. Count the total number of valence electrons around the central atom in each compound, including bonding and lone pairs, to see if the octet is expanded to 12 electrons.
4. For PF6⁻, phosphorus (P) is the central atom and is in period 3, allowing it to expand its octet. It forms six bonds with fluorine atoms, contributing 12 electrons around phosphorus.
5. Compare this with SF6, XeF4, and PCl5, where the number of electrons around the central atom is different, and determine which has exactly 12 electrons in its expanded octet.