Questions: Which of the following atoms contains only three valence electrons: Ar, S, Mg, Al, or Cl ? (Enter your answers as a comma-separated list.)

Solution Steps

To determine the number of valence electrons in an atom, we need to identify the group number of each element in the periodic table. The group number for main-group elements (s and p blocks) typically indicates the number of valence electrons.

• Argon (Ar) is in Group 18.
• Sulfur (S) is in Group 16.
• Magnesium (Mg) is in Group 2.
• Aluminum (Al) is in Group 13.
• Chlorine (Cl) is in Group 17.

Using the group numbers, we can determine the number of valence electrons for each element:

• Argon (Ar): Group 18 elements have 8 valence electrons.
• Sulfur (S): Group 16 elements have 6 valence electrons.
• Magnesium (Mg): Group 2 elements have 2 valence electrons.
• Aluminum (Al): Group 13 elements have 3 valence electrons.
• Chlorine (Cl): Group 17 elements have 7 valence electrons.

From the above analysis, Aluminum (Al) is the element with three valence electrons.

Final Answer