Multiple Choice
Which element forms an ion with an electron configuration of [Ne] and a -2 charge?
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2. Atoms & Elements
Ions
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Which element forms an ion with an electron configuration of [Kr] and a 2− charge?
A
Rb
B
Br
C
Sr
D
Se
Verified step by step guidance1
Identify the electron configuration of the neutral atom for each element given: Rb, Br, Sr, and Se. Recall that the electron configuration of an ion is based on the neutral atom's configuration plus or minus electrons depending on the charge.
Understand that the electron configuration [Kr] corresponds to the electron configuration of the noble gas krypton, which has 36 electrons. This means the ion in question must have 36 electrons total.
Determine the number of electrons in the neutral atom of each element: Rb (Rubidium) has 37 electrons, Br (Bromine) has 35 electrons, Sr (Strontium) has 38 electrons, and Se (Selenium) has 34 electrons.
Since the ion has a 2− charge, it means the element has gained 2 electrons. Add 2 electrons to the neutral atom's electron count and check which element's ion matches 36 electrons (the electron count of [Kr]).
Conclude that the element whose ion has 36 electrons and thus the electron configuration [Kr] with a 2− charge is the one that started with 34 electrons and gained 2 electrons, which corresponds to Selenium (Se).
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