Part B. An unknown element, X, reacts with rubidium to form the compound Rb2X. In other compounds this element also can accommodate up to 12 electrons rather than the usual octet. What element could X be?
When main group elements react, they tend to acquire eight outer-shell electrons (ns2np6). This is called an octet, and it is a particularly stable configuration.
Nonmetals in the third period and beyond can break the octet rule because they have vacant d orbitals that allow them to accommodate more than eight outer-shell electrons.
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