Why can period 1 of the periodic table contain a maximum of two elements?

• A. Because the first energy level (n = 1) has only one s orbital, which can hold a maximum of two electrons.
• B. Because elements in period 1 have the highest electron affinity and cannot accommodate more atoms.
• C. Because the first period includes both s and p orbitals, but only two elements are stable.
• D. Because the atomic radius of period 1 elements is too small to allow more than two elements.

Answer: (A)

Verified step by step guidance

1. Understand that the periodic table is organized based on electron configurations, which depend on the arrangement of electrons in atomic orbitals.
2. Recall that the first energy level (n = 1) contains only one type of orbital: the 1s orbital.
3. Know that each orbital can hold a maximum of two electrons due to the Pauli exclusion principle, which states that no two electrons can have the same set of quantum numbers.
4. Since the 1s orbital is the only orbital in the first energy level and it can hold only two electrons, only two elements can fit in period 1 of the periodic table.
5. Therefore, period 1 contains only hydrogen and helium, corresponding to the filling of the 1s orbital with one and two electrons, respectively.