Multiple Choice
How many valence electrons does bromine (Br) have?
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10. Periodic Properties of the Elements
Valence Electrons of Elements
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Which atom in the ground state has a valence electron with the greatest amount of energy?
A
Li
B
Na
C
K
D
Mg
Verified step by step guidance1
Understand that the valence electron energy depends on the principal quantum number (n) and the effective nuclear charge experienced by the electron. Electrons in higher energy levels (larger n) generally have higher energy.
Identify the electron configurations of the given atoms in their ground states: Li (1s\^2 2s\^1), Na (1s\^2 2s\^2 2p\^6 3s\^1), K (1s\^2 2s\^2 2p\^6 3s\^2 3p\^6 4s\^1), and Mg (1s\^2 2s\^2 2p\^6 3s\^2).
Note that Li, Na, and K are alkali metals with one valence electron in an s orbital, while Mg has two valence electrons in the 3s orbital.
Compare the principal quantum numbers of the valence electrons: Li's valence electron is in n=2, Na's in n=3, K's in n=4, and Mg's valence electrons are in n=3. The higher the n, the higher the energy of the valence electron.
Conclude that potassium (K), with its valence electron in the 4s orbital (n=4), has the valence electron with the greatest amount of energy among the given atoms.
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