What is the ground-state electron configuration of aluminum (atomic number 13)?Answer: 1s2 2s2 2p6 3s2 3p1. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the ground-state electron configuration of argon (atomic number 18)?Answer: 1s2 2s2 2p6 3s2 3p6. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the ground-state electron configuration of carbon (atomic number 6)?Answer: 1s2 2s2 2p2. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the ground-state electron configuration of chlorine (atomic number 17)?Answer: 1s2 2s2 2p6 3s2 3p5. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the ground-state electron configuration of fluorine (atomic number 9)?Answer: 1s2 2s2 2p5. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the ground-state electron configuration of lithium (atomic number 3)?Answer: 1s2 2s1. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Show all 69 questions (63 more)
Configurations, continued
What is the ground-state electron configuration of neon (atomic number 10)?Answer: 1s2 2s2 2p6. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the ground-state electron configuration of nitrogen (atomic number 7)?Answer: 1s2 2s2 2p3. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the ground-state electron configuration of oxygen (atomic number 8)?Answer: 1s2 2s2 2p4. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the ground-state electron configuration of phosphorus (atomic number 15)?Answer: 1s2 2s2 2p6 3s2 3p3. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the ground-state electron configuration of sodium (atomic number 11)?Answer: 1s2 2s2 2p6 3s1. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the noble-gas short form of the ground-state configuration of calcium (atomic number 20)?Answer: [Ar] 4s2. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the noble-gas short form of the ground-state configuration of chromium (atomic number 24)?Answer: [Ar] 4s1 3d5. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the noble-gas short form of the ground-state configuration of copper (atomic number 29)?Answer: [Ar] 4s1 3d10. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the noble-gas short form of the ground-state configuration of iron (atomic number 26)?Answer: [Ar] 4s2 3d6. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the noble-gas short form of the ground-state configuration of magnesium (atomic number 12)?Answer: [Ne] 3s2. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the noble-gas short form of the ground-state configuration of manganese (atomic number 25)?Answer: [Ar] 4s2 3d5. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the noble-gas short form of the ground-state configuration of potassium (atomic number 19)?Answer: [Ar] 4s1. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the noble-gas short form of the ground-state configuration of scandium (atomic number 21)?Answer: [Ar] 4s2 3d1. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the noble-gas short form of the ground-state configuration of silicon (atomic number 14)?Answer: [Ne] 3s2 3p2. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the noble-gas short form of the ground-state configuration of sulfur (atomic number 16)?Answer: [Ne] 3s2 3p4. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the noble-gas short form of the ground-state configuration of titanium (atomic number 22)?Answer: [Ar] 4s2 3d2. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
What is the noble-gas short form of the ground-state configuration of zinc (atomic number 30)?Answer: [Ar] 4s2 3d10. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Which element has the ground-state configuration 1s1?Answer: Hydrogen. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Which element has the ground-state configuration [Ar] 4s2 3d3?Answer: Vanadium. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Which element has the ground-state configuration [Ar] 4s2 3d8?Answer: Nickel. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Which element's ground-state configuration is 1s2 2s2 2p1?Answer: Boron. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Which element's ground-state configuration is 1s2 2s2?Answer: Beryllium. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Which element's ground-state configuration is 1s2?Answer: Helium. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Orbital diagrams 23
A student drew this for the ground state of beryllium. Which rule, if any, does it break? (Picture: A row of boxes with arrows. 1s: a pair. 2s: down and down.)Answer: The Pauli exclusion principle. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
A student drew this for the ground state of carbon. Which rule, if any, does it break? (Picture: A row of boxes with arrows. 1s: a pair. 2s: a pair. 2p: a pair, empty, empty.)Answer: Hund's rule. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
A student drew this for the ground state of carbon. Which rule, if any, does it break? (Picture: A row of boxes with arrows. 1s: a pair. 2s: up. 2p: up, up, up.)Answer: The aufbau principle. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
A student drew this for the ground state of lithium. Which rule, if any, does it break? (Picture: A row of boxes with arrows. 1s: a pair. 2s: empty. 2p: up, empty, empty.)Answer: The aufbau principle. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
A student drew this for the ground state of lithium. Which rule, if any, does it break? (Picture: A row of boxes with arrows. 1s: up and up. 2s: up.)Answer: The Pauli exclusion principle. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
A student drew this for the ground state of nitrogen. Which rule, if any, does it break? (Picture: A row of boxes with arrows. 1s: a pair. 2s: a pair. 2p: a pair, up, empty.)Answer: Hund's rule. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
A student drew this for the ground state of nitrogen. Which rule, if any, does it break? (Picture: A row of boxes with arrows. 1s: a pair. 2s: a pair. 2p: up, down, up.)Answer: Hund's rule. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
A student drew this for the ground state of oxygen. Which rule, if any, does it break? (Picture: A row of boxes with arrows. 1s: a pair. 2s: a pair. 2p: a pair, up, up.)Answer: No rule: it is a correct ground state. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
A student drew this for the ground state of silicon. Which rule, if any, does it break? (Picture: A row of boxes with arrows that starts with [Ne]. 3s: a pair. 3p: up, up, empty.)Answer: No rule: it is a correct ground state. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
How many unpaired electrons does this orbital diagram show? (Picture: A row of boxes with arrows that starts with [Ne]. 3s: a pair. 3p: up, empty, empty.)Answer: One. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
How many unpaired electrons does this orbital diagram show? (Picture: A row of boxes with arrows. 1s: a pair. 2s: a pair. 2p: a pair, a pair, a pair.)Answer: None. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
How many unpaired electrons does this orbital diagram show? (Picture: A row of boxes with arrows. 1s: a pair. 2s: a pair. 2p: a pair, up, up.)Answer: Two. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
How many unpaired electrons does this orbital diagram show? (Picture: A row of boxes with arrows. 1s: a pair. 2s: a pair. 2p: up, up, up.)Answer: Three. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
Which element has this orbital diagram in its ground state? (Picture: A row of boxes with arrows that starts with [Ne]. 3s: a pair. 3p: a pair, up, up.)Answer: Sulfur. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Which element has this orbital diagram in its ground state? (Picture: A row of boxes with arrows that starts with [Ne]. 3s: a pair. 3p: up, up, empty.)Answer: Silicon. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Which element has this orbital diagram in its ground state? (Picture: A row of boxes with arrows that starts with [Ne]. 3s: a pair. 3p: up, up, up.)Answer: Phosphorus. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Which element has this orbital diagram in its ground state? (Picture: A row of boxes with arrows that starts with [Ne]. 3s: up.)Answer: Sodium. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Which element has this orbital diagram in its ground state? (Picture: A row of boxes with arrows. 1s: a pair. 2s: a pair. 2p: a pair, a pair, up.)Answer: Fluorine. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Which element has this orbital diagram in its ground state? (Picture: A row of boxes with arrows. 1s: a pair. 2s: a pair. 2p: a pair, up, up.)Answer: Oxygen. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Which element has this orbital diagram in its ground state? (Picture: A row of boxes with arrows. 1s: a pair. 2s: a pair. 2p: up, empty, empty.)Answer: Boron. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Which element has this orbital diagram in its ground state? (Picture: A row of boxes with arrows. 1s: a pair. 2s: a pair. 2p: up, up, empty.)Answer: Carbon. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Which element has this orbital diagram in its ground state? (Picture: A row of boxes with arrows. 1s: a pair. 2s: a pair. 2p: up, up, up.)Answer: Nitrogen. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Which element has this orbital diagram in its ground state? (Picture: A row of boxes with arrows. 1s: a pair. 2s: up.)Answer: Lithium. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
Rules 17
An atom has the configuration 1s2 2s2 2p5. How many valence electrons does it have?Answer: 7 electrons. Source: Purdue University chemistry review, Valence Electrons, and Wikipedia, Valence electron. Read 2026-10-01.
An atom has the configuration 1s2 2s2 2p6 3s2 3p3. How many valence electrons does it have?Answer: 5 electrons. Source: Purdue University chemistry review, Valence Electrons, and Wikipedia, Valence electron. Read 2026-10-01.
How many boxes does a p subshell get in an orbital diagram?Answer: Three boxes. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
How many electrons can one orbital hold?Answer: 2 electrons. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
How many electrons fill a d subshell?Answer: 10 electrons. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
How many electrons fill a p subshell?Answer: 6 electrons. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
How many electrons fill an f subshell?Answer: 14 electrons. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
How many electrons fill an s subshell?Answer: 2 electrons. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
In an orbital diagram, what does one arrow stand for?Answer: One electron. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
What does [Ne] stand for in [Ne] 3s1?Answer: The ten electrons of neon, 1s2 2s2 2p6. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
Which rule means two electrons in the same orbital must have opposite spins?Answer: The Pauli exclusion principle. Source: Wikipedia, Pauli exclusion principle, and Georgia State University, HyperPhysics, Pauli Exclusion Principle. Read 2026-10-01.
Which rule puts one electron in each orbital of a subshell before any of them pairs up?Answer: Hund's rule. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
Which rule says electrons go into the lowest-energy orbital that still has room?Answer: The aufbau principle. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
Which subshell fills right after 2p?Answer: 3s. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
Which subshell fills right after 3p?Answer: 4s. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
Which subshell fills right after 4s?Answer: 3d. Source: Purdue University chemistry review, Electron Configurations, and Wikipedia, Aufbau principle and Hund's rule. Read 2026-10-01.
Which two elements of the first four rows do not follow the predicted filling order?Answer: Chromium and copper. Source: NIST Atomic Spectra Database, ground states, and the Purdue University chemistry review. Read 2026-10-01.
This electron configuration and orbital diagram quiz runs from hydrogen to zinc. Pick an atom's ground-state configuration, name the element behind a row of boxes and arrows, and spot which filling rule a wrong diagram breaks.
Read the full guide
Three sets
Configurations asks the full form, 1s2 2s2 2p4 for oxygen, and the noble-gas short form; exponents are written as plain digits. Orbital diagrams shows boxes and arrows. Rules asks the filling order and how many electrons each subshell holds.
Reading a diagram
Each box is one orbital and each arrow is one electron. Diagrams for sodium to argon start with [Ne] and show the third shell only.
Play or print
Tap a choice and the answer shows at once, with the reason. A round is ten questions. After a round, Print lists its questions: add more, tick With answer key, and print.
4s fills before 3d, so potassium is [Ar] 4s1.
Chromium and copper each keep one 4s electron: the two exceptions before zinc.
Questions and answers
What is the difference between an electron configuration and an orbital diagram?
A configuration counts the electrons in each subshell, such as 1s2 2s2 2p3 for nitrogen. An orbital diagram draws each orbital as a box and each electron as an arrow, so it also shows which electrons are paired.
What is Hund's rule?
Electrons enter the orbitals of one subshell one at a time, with the same spin, before any orbital takes a second electron. Carbon's two 2p electrons sit in two different boxes, both arrows up.
Why is chromium 4s1 3d5 and not 4s2 3d4?
The filling order predicts 4s2 3d4, but the measured ground state of chromium is [Ar] 4s1 3d5. Copper is the other exception among the first thirty elements: [Ar] 4s1 3d10.
Is 4s written before or after 3d?
Both ways are in use. This quiz writes the subshells in the order they fill, 4s and then 3d. Some reference tables list them by shell number, 3d and then 4s. The electrons counted are the same.
How many electrons can each subshell hold?
An s subshell holds 2 electrons, a p subshell 6, a d subshell 10 and an f subshell 14. Each orbital holds two electrons with opposite spins.