Multiple Choice
How many s electrons are present in a neutral atom of phosphorus (atomic number 15)?
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10. Periodic Properties of the Elements
Valence Electrons of Elements
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Which of the following is the best method to determine the number of valence electrons in a neutral atom of a main group element?
A
Count the total number of electrons in the atom.
B
Divide the atomic number by two.
C
Check the group number of the element in the periodic table (for groups 1–2 and 13–18).
D
Subtract the atomic number from the mass number.
Verified step by step guidance1
Understand that valence electrons are the electrons in the outermost shell of an atom that participate in chemical bonding.
Recall that for main group elements (groups 1–2 and 13–18), the group number corresponds to the number of valence electrons. For example, elements in group 1 have 1 valence electron, group 2 have 2 valence electrons, and groups 13–18 have 3 to 8 valence electrons respectively.
Recognize that counting the total number of electrons or dividing the atomic number by two does not reliably give the number of valence electrons because inner electrons do not participate in bonding.
Note that subtracting the atomic number from the mass number gives the number of neutrons, which is unrelated to valence electrons.
Therefore, the best method is to check the group number of the element in the periodic table (for groups 1–2 and 13–18) to determine the number of valence electrons.
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