Multiple Choice
For a sodium atom (Na), in which principal energy level are the valence electron(s) found?
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10. Periodic Properties of the Elements
Valence Electrons of Elements
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How many valence electrons does strontium (Sr) have?
A
8
B
4
C
2
D
6
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.
Determine the electron configuration of Sr by filling the orbitals in order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, etc., until all 38 electrons are placed.
Recognize that valence electrons are the electrons in the outermost shell (highest principal quantum number, n). For Sr, this corresponds to the electrons in the 5s orbital.
Count the number of electrons in the outermost shell (5s orbital) to find the number of valence electrons.
Conclude that strontium has 2 valence electrons because its outermost shell contains two electrons in the 5s orbital.
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