Electron Configuration Quiz
Questions: 16 · 10 minutes
1. Neutral iron is [Ar] 3d⁶ 4s². If its two 4s electrons are removed to form Fe²⁺, what configuration results?
[Ar] 3d⁴ 4s² — two electrons removed from 3d instead
[Ar] 3d⁵ 4s¹ — one electron removed from each occupied subshell
[Ar] 3d⁶ — both 4s electrons removed
[Ar] 3d⁸ — two electrons added to 3d
2. Which principle most directly explains why a ground-state atom fills the lower-energy 3s subshell before the 3p subshell?
Hund's rule, which governs occupancy within equal-energy orbitals
The Aufbau principle, which directs electrons toward lower-energy orbitals first
The octet rule, which describes a common valence-shell pattern
The Pauli exclusion principle, which limits occupancy within one orbital
3. Magnesium changes from [Ne] 3s² to [Ne] when it forms Mg²⁺. What does this change show?
The ion has gained a newly occupied electron shell.
The ion has two more valence electrons than the neutral atom.
The ion and neutral atom contain identical numbers of electrons.
The ion has lost both 3s electrons, leaving the third shell unoccupied.
4. Which option can represent an excited state of a neutral carbon atom?
1s² 2s¹ 2p³ — six electrons with one electron promoted from 2s to 2p
1s² 2s² 2p³ — a seven-electron arrangement
1s² 2s³ 2p¹ — an impossible occupancy for an s subshell
1s² 2s² 2p² — carbon's ground-state subshell configuration
5. A student writes potassium's ground-state configuration as [Ar] 3d¹. Which correction follows the usual filling order?
[Ar] 4s¹, placing the nineteenth electron in the lower-energy 4s subshell
[Ar] 3d², adding another electron to the same subshell
[Ne] 3s² 3p⁶, which accounts for only eighteen electrons
[Ar] 4p¹, skipping both the 4s and 3d subshells
6. Which notation exceeds the maximum capacity of the indicated subshell?
3d¹⁰, showing a completely filled d subshell
2p⁷, showing seven electrons where only six can fit
1s², showing a completely filled s subshell
4f¹⁴, showing a completely filled f subshell
7. An unknown main-group atom has the outer configuration 3s² 3p¹. In which periodic-table group is it found?
Group 2, because the 3s subshell contains two electrons
Group 18, because the third energy level is occupied
Group 16, because a p subshell can hold six electrons
Group 13, because the atom has three outer-shell electrons
8. An orbital diagram for sulfur shows four electrons distributed across its three 3p orbitals according to Hund's rule. How many of those electrons are unpaired?
Two unpaired electrons, because one orbital is paired and two are singly occupied
No unpaired electrons, because all four form two pairs
One unpaired electron, because only the last electron remains single
Four unpaired electrons, even though only three p orbitals are available
9. Which element has the ground-state shorthand configuration [Ne] 3s² 3p⁵?
Sulfur, whose 3p subshell contains four electrons
Argon, whose 3p subshell is completely filled
Chlorine, with seven electrons beyond the neon core
Phosphorus, whose 3p subshell contains three electrons
10. Which shorthand configuration represents a neutral iron atom in its ground state?
[Ar] 3d⁶ 4s² — 26 electrons in total
[Ar] 3d⁸ — 26 electrons but with the 4s occupancy omitted
[Ne] 3d⁶ 4s² — only 18 electrons in total
[Kr] 3d⁶ 4s² — more electrons than neutral iron possesses
11. A neutral sodium atom loses its outermost electron to form Na⁺. Which option gives the ion's configuration?
1s² 2s² 2p⁶ 3s² — twelve electrons after filling the 3s orbital
1s² 2s² 2p⁶ 3s¹ — the unchanged neutral-sodium arrangement
1s² 2s² 2p⁵ 3s¹ — one electron removed from the 2p subshell
1s² 2s² 2p⁶ — ten electrons with the former 3s electron removed
12. Which statement correctly describes the Pauli exclusion principle?
Electrons occupy equal-energy orbitals singly before any pairing occurs.
Electrons enter the orbital farthest from the nucleus before lower-energy orbitals.
One orbital can contain at most two electrons, and those electrons must have opposite spins.
Every occupied subshell must contain an even number of electrons.
13. Which option gives the ground-state electron configuration of a neutral oxygen atom?
1s² 2s¹ 2p⁵ — eight electrons with an unfilled 2s subshell
1s² 2s² 2p⁶ — the ten-electron neon arrangement
1s² 2s² 2p⁴ — eight electrons filled in ground-state order
1s² 2s² 3p⁴ — electrons placed in 3p before 2p
14. A ground-state carbon atom has two electrons in its three 2p orbitals. Which arrangement follows Hund's rule?
Both electrons pair in the first 2p orbital while the other two remain empty.
Only one of the two electrons is placed in the 2p subshell.
The two electrons occupy separate 2p orbitals with opposite spin directions.
The two electrons occupy separate 2p orbitals with parallel spins.
15. What is the maximum number of electrons that can occupy an entire p subshell?
Two electrons, the capacity of one orbital
Six electrons, distributed across three p orbitals
Four electrons, leaving one p orbital empty
Ten electrons, the capacity associated with a d subshell
16. A chloride ion, Cl⁻, contains 18 electrons. Which neutral atom is isoelectronic with it?
Neon, which has 10 electrons
Argon, which has 18 electrons
Potassium, which has 19 electrons
Sulfur, which has 16 electrons