Multiple Choice
How many valence electrons does aluminum (Al) have?
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9. Electrons in Atoms and the Periodic Table
Valence Electrons of Elements (Simplified)
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For a main-group element, how can you determine the number of valence electrons using the periodic table?
A
Use the element’s group number (1–2 give 1–2 valence electrons; 13–18 give 3–8 valence electrons, with helium as an exception having 2).
B
Use the element’s atomic number; the atomic number equals the number of valence electrons.
C
Use the element’s average atomic mass; the atomic mass equals the number of valence electrons.
D
Use the element’s period number; the period number equals the number of valence electrons.
Verified step by step guidance1
Understand that valence electrons are the electrons in the outermost shell of an atom and are important because they determine the chemical properties and bonding behavior of the element.
Identify that for main-group elements (those in groups 1, 2, and 13 through 18), the number of valence electrons can be found using the group number on the periodic table.
Recall the rule: elements in groups 1 and 2 have 1 and 2 valence electrons respectively, while elements in groups 13 through 18 have valence electrons equal to the group number minus 10 (for example, group 13 elements have 3 valence electrons, group 14 have 4, and so on).
Note the exception that helium, although in group 18, has 2 valence electrons because its outer shell is the first shell, which can hold only 2 electrons.
Recognize that atomic number, atomic mass, and period number do not directly give the number of valence electrons, so the correct method is to use the group number as described.
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