Question

which statement best describes how electrons fill orbitals in the periodic table?

• electrons fill orbitals in order of their increasing energy from left to right.
• electrons fill orbitals in order of their increasing energy from right to left.
• elements fill orbitals in order of increasing energy from top to bottom in each group.
• elements fill orbitals in order of increasing energy from bottom to top in each group.

Explanation:

To determine the correct statement about electron orbital filling in the periodic table, we recall the Aufbau principle (and related concepts like the Madelung rule). Electrons fill orbitals in order of increasing energy. Looking at the periodic table, as we move from left to right across a period, the energy of the orbitals being filled generally increases (due to increasing nuclear charge and filling of subshells in order of increasing energy, like \(1s \to 2s \to 2p \to 3s \to 3p \to 4s \to 3d \), etc.).

• The second option is incorrect because electrons do not fill from right to left (left - to - right is the direction of increasing proton number and orbital energy filling in periods).
• The third option: In a group (vertical column), as we go from top to bottom, the principal quantum number \(n\) increases, but the filling order of orbitals for elements in a group is not about filling from top to bottom in terms of energy order for orbital filling (the energy of orbitals with higher \(n\) is higher, but the filling of orbitals across the periodic table follows the period - wise left - to - right order for energy - increasing orbital filling).
• The fourth option is incorrect as filling from bottom to top in a group is not how orbital filling energy order works.

The first option correctly states that electrons fill orbitals in order of their increasing energy from left to right (across a period, which corresponds to filling orbitals of increasing energy as per the Aufbau principle).

Answer:

A. Electrons fill orbitals in order of their increasing energy from left to right.