The _____ in the group tells the number of valence electrons in that element

• A. Last Number
• B. Group Number
• C. Period Number
• D. Atomic Number

Answer: (A)

Valence electrons are the outermost electrons involved in bonding. For the main-group elements, the number of valence electrons is given by the column you’re in on the periodic table—the group number. So, the group tells you directly how many electrons are in the outer shell.

The period number tells which shell those outer electrons occupy (the energy level), not how many there are. The atomic number counts total protons (and, in a neutral atom, total electrons), not specifically the valence electrons. “Last Number” isn’t a standard way to describe this property.

For examples, elements in the first group have one valence electron, those in the sixteenth group have six, and so on. This makes the group number the best indicator of valence electrons for most elements.