What best describes Groups in the periodic table?

• A. Vertical columns, each element in a group has the same number of valence electrons and typically behave in a similar manner when bonding with other elements
• B. Horizontal rows
• C. A set of elements with identical atomic numbers
• D. The bottom two rows

Answer: (A)

Groups are vertical columns in the periodic table. In a group, elements tend to have the same number of valence electrons, which largely controls how they bond and the kinds of compounds they form. Because valence electrons drive bonding patterns, elements in the same group exhibit similar chemical behavior and form comparable ions and compounds. For example, elements in one group typically form +1 ions, or in another group form -1 ions, and so on, reflecting their shared valence electron count.

The horizontal rows are periods, not groups, so that description doesn’t fit. A set of elements with identical atomic numbers isn’t possible, since each element has a unique atomic number. The bottom two rows refer to the lanthanide and actinide series, which are not groups. This vertical-column description with the common valence-electron count best captures what groups are.