Which of the following statements is false?

• A. The sublevels of each principal level are not degenerate for multielectron atoms.
• B. In a hydrogen atom, the sublevels of each principal level are degenerate.
• C. Due to shielding, the 3d orbitals lie lower in energy than the 4s orbital.
• D. Some atoms have anomalies in their electron configurations due to the fact that energy separations of the orbitals become smaller as the principal quantum number increases.

Answer: (C)

Verified step by step guidance

1. Understand the concept of degeneracy: In quantum chemistry, degeneracy refers to the condition where two or more orbitals have the same energy level. For hydrogen atoms, all sublevels within a principal energy level are degenerate because there is only one electron and no electron-electron repulsions.
2. Consider multielectron atoms: In multielectron atoms, electron-electron interactions cause sublevels within the same principal energy level to have different energies, meaning they are not degenerate.
3. Analyze the statement about 3d and 4s orbitals: In multielectron atoms, the 4s orbital is typically filled before the 3d orbital because it is lower in energy. However, after the 3d orbitals start filling, they become lower in energy than the 4s orbital due to electron-electron interactions and shielding effects.
4. Examine electron configuration anomalies: Some elements exhibit anomalies in their electron configurations, such as chromium and copper, due to the small energy differences between 3d and 4s orbitals. This can lead to unexpected electron configurations that minimize the overall energy of the atom.
5. Identify the false statement: The statement 'Due to shielding, the 3d orbitals lie lower in energy than the 4s orbital' is false in the context of initial electron filling order. Initially, 4s is lower in energy than 3d, but after 3d starts filling, it becomes lower in energy than 4s.