Final answer:
Out of the interhalogen species ClF₃, ClF₂⁻, ClF5, ICl₂⁺, and I₇⁻, only ClF₃ and ICl₂⁺ have exactly two lone pairs of electrons on the central atom.
Step-by-step explanation:
The student asked how many of the interhalogen species ClF₃, ClF₂⁻, ClF5, ICl₂⁺, and I₇⁻ have two lone pairs of electrons on the central atom. To find this out, we must consider the valence electron count of the central halogen and apply the octet rule alongside other concepts such as hypervalent molecules and Lewis structures.
A halogen typically has seven valence electrons. In ClF₃, chlorine is the central atom and forms three bonds with fluorine atoms, leaving two lone pairs on the central chlorine atom. ClF₂⁻ is similar but has an extra electron due to the negative charge, resulting in three lone pairs on the central chlorine. ClF5 has chlorine surrounded by five fluorine atoms with one lone pair on chlorine as it follows the hypervalent molecule structure. ICl₂⁺, with iodine as the central atom, also has two lone pairs due to the positive charge reducing the number of lone pairs from three to two. Finally, I₇⁻ is an unusual species, but if considering iodine in a similar arrangement to ICl₂⁺, it would likely possess more than two lone pairs due to the negative charge. Therefore, out of the listed interhalogen species, only ClF₃ and ICl₂⁺ have exactly two lone pairs of electrons on the central atom.