Scelta multipla
What is the term used to describe the outermost electrons in an atom?
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10. Periodic Properties of the Elements
Valence Electrons of Elements
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An atom has 15 total electrons. How many electrons does it have in its outer (valence) shell?
A
3
B
7
C
5
D
8
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Identify the element by its total number of electrons. Since the atom has 15 electrons, it corresponds to the element with atomic number 15, which is phosphorus (P).
Determine the electron configuration of the atom by filling the electron shells in order of increasing energy levels: 1s, 2s, 2p, 3s, 3p, etc.
Write the electron configuration for 15 electrons: 1s\^2 2s\^2 2p\^6 3s\^2 3p\^3.
Recognize that the outer (valence) shell is the highest principal energy level occupied by electrons, which here is the third shell (n=3).
Count the electrons in the outer shell: 3s\^2 and 3p\^3 add up to 2 + 3 = 5 valence electrons.
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