Practice question · True or false
The 4s subshell is filled before the 3d subshell in the neutral atoms of the fourth period.
Hints
- Compare the energies, not the shell numbers.
- The 4s orbital penetrates closer to the nucleus and sits slightly lower in energy.
Show the answer
True
Why
True, although is larger, the orbital penetrates more effectively toward the nucleus and lies slightly below in the neutral atom, so it fills first. It also ionises first, which surprises many students.
Practise Orbitals, Quantum Numbers and Electron Configuration
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More questions on Orbitals, Quantum Numbers and Electron Configuration
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- Complete the statement of the three filling rules.
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- In a hydrogen atom the 2s and 2p orbitals have equal energy, but in lithium the 2s lies lower. Why?