Multiple Choice
When an electron moves from the first energy level (n = 1) to the second energy level (n = 2) in an atom, which of the following occurs?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of these elements has an electron configuration of [Kr]5s2?
A
Y
B
Sr
C
Rb
D
Zr
Verified step by step guidance1
Recall that the electron configuration notation [Kr] represents the electron configuration of the noble gas krypton, which has 36 electrons.
Understand that the configuration [Kr]5s2 means the element has all the electrons of krypton plus 2 electrons in the 5s subshell.
Identify the atomic number of krypton (Kr), which is 36, and then add 2 electrons to account for the 5s2 configuration, giving a total of 38 electrons.
Look up the element with atomic number 38, which corresponds to strontium (Sr).
Confirm that the other elements listed (Y, Rb, Zr) have different electron configurations: Y (39) is [Kr]5s2 4d1, Rb (37) is [Kr]5s1, and Zr (40) is [Kr]5s2 4d2.
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