Multiple Choice
How many valence electrons are present in a neutral atom of neon (Ne)?
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10. Periodic Properties of the Elements
Valence Electrons of Elements
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Which of the following represents the configuration of the valence electrons in cobalt (Co)?
A
3d^6 4s^2
B
3d^8 4s^1
C
3d^7 4s^2
D
3d^5 4s^2
Verified step by step guidance1
Identify the atomic number of cobalt (Co), which is 27. This means cobalt has 27 electrons in total.
Recall that the electron configuration fills orbitals in order of increasing energy, generally following the Aufbau principle: 1s, 2s, 2p, 3s, 3p, 4s, 3d, etc.
Write the full electron configuration of cobalt up to the 3d and 4s orbitals. The 4s orbital fills before the 3d orbitals, so after filling 1s through 3p, the next electrons go into 4s and then 3d.
Determine the number of electrons in the 3d and 4s orbitals for cobalt by subtracting the electrons accounted for in the lower energy orbitals from the total 27 electrons.
Express the valence electron configuration focusing on the 3d and 4s orbitals, which are the outermost electrons for cobalt, and compare it to the given options to identify the correct configuration.
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