Which factor determines the length of each period in the periodic table?

• A. The number of electrons that can occupy the available energy levels (shells) for that period
• B. The number of valence electrons in the outermost shell
• C. The atomic mass of the elements in that period
• D. The chemical reactivity of the elements in that period

Answer: (A)

Verified step by step guidance

1. Understand that the periodic table is arranged in periods (rows) where each period corresponds to the filling of a specific principal energy level (shell) with electrons.
2. Recall that each principal energy level can hold a certain maximum number of electrons, determined by the formula \$2n^2\(, where \)n$ is the principal quantum number (energy level).
3. Recognize that the length of each period depends on how many electrons can fit into the available subshells (s, p, d, f) within that principal energy level.
4. Note that the number of elements in a period equals the number of electrons needed to fill the energy level associated with that period, which is why periods vary in length.
5. Conclude that the factor determining the length of each period is the number of electrons that can occupy the available energy levels (shells) for that period, not the atomic mass, valence electrons alone, or chemical reactivity.