Multiple Choice
Which of the following is the correct electron configuration for cesium (Cs)?
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10. Periodic Properties of the Elements
The Electron Configuration
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Which of the following represents the electron configuration for the valence electrons in strontium (Sr)?
A
3d10 4s2
B
4s2 4p6
C
4d10
D
5s2
Verified step by step guidance1
Identify the atomic number of strontium (Sr), which is 38. This tells us the total number of electrons in a neutral Sr atom.
Recall that electron configurations are filled according to the Aufbau principle, filling lower energy orbitals first: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, and so on.
Determine the valence shell for strontium. Since Sr is in period 5 and group 2 of the periodic table, its valence electrons are in the 5th shell, specifically the 5s orbital.
Write the electron configuration up to the valence electrons, focusing on the outermost shell: the 5s orbital contains 2 electrons, so the valence electron configuration is $5s^2$.
Compare the given options to the valence electron configuration. The correct representation for Sr's valence electrons is $5s^2$, as it reflects the electrons in the outermost shell responsible for chemical behavior.
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