Multiple Choice
Which of the following electron configurations represents an atom of chlorine (atomic number 17) in an excited state?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following ions has the electron configuration 1s^2 2s^2 2p^6?
A
F^-
B
Na^+
C
O^2-
D
Mg^2+
Verified step by step guidance1
Identify the electron configuration given: $1s^2 2s^2 2p^6$. This corresponds to a total of 10 electrons, which is the electron configuration of the noble gas neon (Ne).
Determine the number of electrons in each ion by considering the atomic number and the charge of the ion. For example, fluorine (F) has an atomic number of 9, so F$^-$ has 9 + 1 = 10 electrons.
Repeat this for each ion: Na$^+$ (atomic number 11, loses 1 electron, so 11 - 1 = 10 electrons), O$^{2-}$ (atomic number 8, gains 2 electrons, so 8 + 2 = 10 electrons), Mg$^{2+}$ (atomic number 12, loses 2 electrons, so 12 - 2 = 10 electrons).
Compare the number of electrons in each ion to the electron configuration given (10 electrons). All ions with 10 electrons will have the electron configuration $1s^2 2s^2 2p^6$.
Confirm which ion matches the electron configuration exactly by considering the charge and atomic number, and select the correct ion accordingly.
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