Which of the following notations is the correct noble gas configuration for Co?
A. $[Ar] 4s^2 4p^6 3d^1$
B. $[Kr] 4s^2 4p^6 4d^1$
C. $[Co] 4s^2 3d^7$
D. $[Ar] 4s^2 3d^7$
Answer (2)
Cobalt (Co) has 27 electrons.
Argon (Ar) is the preceding noble gas with 18 electrons.
Remaining electrons: 27 − 18 = 9 .
The correct noble gas configuration for Cobalt (Co) is [ A r ] 4 s 2 3 d 7 .
Explanation
Understanding the Problem We need to determine the correct noble gas configuration for Cobalt (Co). Cobalt has an atomic number of 27, meaning it has 27 electrons. We need to find the noble gas that comes before Cobalt in the periodic table to use as our starting point.
Identifying the Preceding Noble Gas The noble gas that precedes Cobalt (Co) is Argon (Ar), which has an atomic number of 18. This means Argon's electron configuration is 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 .
Calculating Remaining Electrons After Argon, we need to account for the remaining electrons in Cobalt. Cobalt has 27 electrons, and Argon has 18, so we need to account for 27 − 18 = 9 more electrons.
Filling Remaining Orbitals These 9 electrons will fill the 4 s and 3 d orbitals. The 4 s orbital fills first with 2 electrons, so we have 4 s 2 . This leaves 9 − 2 = 7 electrons to fill the 3 d orbital, resulting in 3 d 7 .
Determining the Correct Configuration Therefore, the correct noble gas configuration for Cobalt (Co) is [ A r ] 4 s 2 3 d 7 . Comparing this to the given options, we see that option D matches our result.
Examples
Understanding electron configurations helps predict how elements will interact to form chemical bonds. For example, knowing Cobalt's electron configuration allows us to understand its magnetic properties and how it forms complexes with other elements, which is crucial in designing catalysts or understanding the behavior of alloys. This knowledge is also vital in fields like materials science and quantum computing, where the electronic structure of materials determines their functionality.
The correct noble gas configuration for Cobalt (Co), which has 27 electrons, is [Ar] 4s² 3d⁷. This is derived by using Argon ([Ar]) as the preceding noble gas and accounting for the remaining 9 electrons. The answer is option D: [Ar] 4s² 3d⁷.
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