Final answer:
The central atom most likely to violate the octet rule is in SF6, where sulfur has twelve valence electrons, and in XeF4, where xenon also has twelve valence electrons, both exhibiting expanded valence shells.
Step-by-step explanation:
The species in which the central atom is likely to violate the octet rule is SF6 (Sulfur Hexafluoride). The octet rule states that atoms tend to combine in such a way that they each have eight electrons in their valence shells, giving them the same electronic configuration as a noble gas. However, there are exceptions, and one of them occurs in molecules where the central atom can have more than eight electrons around it, often due to the presence of d orbitals in the valence shell.
In SF6, sulfur has twelve electrons in its valence shell when forming six bonds with fluorine atoms. And in XeF4 (Xenon Tetrafluoride), xenon has twelve valence electrons when forming four bonds with fluorine atoms, which is another example of octet rule violation. Xenon is a noble gas and can expand its valence shell due to the availability of d orbitals.
To understand these exceptions better, let's consider the Lewis electron dot diagrams:
- SF6: S surrounded by six F atoms, each sharing one pair of electrons with S, resulting in a total of twelve electrons around S.
- XeF4: Xe with four F atoms, each sharing one pair of electrons with Xe, plus two lone pairs on Xe, resulting in a total of twelve electrons around Xe.