Multiple Choice
How many valence electrons does helium (He) have?
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10. Periodic Properties of the Elements
Valence Electrons of Elements
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Which of the following represents the valence electron configuration for a krypton (Kr) atom?
A
3d^{10} 4s^2 4p^6
B
4s^2 4p^5
C
3s^2 3p^6
D
4s^2 4p^6
Verified step by step guidance1
Identify the atomic number of krypton (Kr), which is 36. This tells us the total number of electrons in a neutral Kr atom.
Recall that valence electrons are the electrons in the outermost shell (highest principal quantum number, n) of an atom that participate in chemical bonding.
Determine the electron configuration of krypton by filling orbitals in order of increasing energy: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, etc., until all 36 electrons are placed.
Recognize that the valence shell for krypton corresponds to the 4th energy level, which includes the 4s and 4p orbitals. The 3d orbitals are part of the third shell and are considered inner electrons for Kr.
Write the valence electron configuration by including only the electrons in the 4s and 4p orbitals, which for krypton is $4s^{2} 4p^{6}$.
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