Writing electron configurations is a skill that only sticks with practice. This quiz draws a new question every time you press “New question” – a random element or ion from the range you choose, so beginners can stay with the first 20 elements and advanced students can include the transition metals, lanthanides and their exceptions.
There are seven kinds of question: the full configuration, the noble-gas shorthand, the configuration of a common ion (Fe³⁺, Cu⁺, S²⁻ …), the number of valence electrons, the number of unpaired electrons, “which element has this configuration?”, and conceptual multiple-choice questions on subshell capacities, the n + l filling order, Hund’s rule and the Pauli exclusion principle.
Type your answer the way you would on paper – 1s2 2s2 2p6, 1s^2 2s^2, [Ne] 3s² 3p⁴ or even 3d104s2 all work, in any subshell order. The quiz compares the electron counts, so it does not mind formatting. If you write the plain Aufbau prediction for an exception such as chromium or copper, it tells you so. A worked answer appears as soon as you are right, or when you choose to show it, and your score for the session is kept on the page.
How to use the Electron Configuration Quiz
- Question type
- Elements included
- Your answer — Configuration (1s2 2s2 2p6 or [Ne] 3s2), a number, an element symbol or A–D.
- Show the answer
Everything is calculated in your browser, so results appear instantly and nothing you type is sent to a server.
How it works
Each question is generated from the built-in periodic table: the correct configuration comes from the Madelung filling order with the measured exceptions, ion configurations remove the outermost electrons first, and conceptual questions are drawn from a bank with shuffled options. Your typed configuration is parsed into subshell counts and compared with the answer.
Worked example
Question: “Write the noble-gas configuration of manganese (Mn, Z = 25).” The previous noble gas is argon (18 electrons), leaving 7: two go into 4s and five into 3d. Answer: [Ar] 3d⁵ 4s² (also accepted: [Ar] 4s² 3d⁵ or the full 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁵). With five singly occupied 3d orbitals, manganese has 5 unpaired electrons.
Question types
| Type | Example | Answer format |
|---|---|---|
| Full configuration | Sulfur (Z = 16) | 1s2 2s2 2p6 3s2 3p4 |
| Noble-gas shorthand | Iron (Z = 26) | [Ar] 3d6 4s2 |
| Ion | Cu²⁺ | [Ar] 3d9 |
| Valence electrons | Gallium | 3 |
| Unpaired electrons | Nitrogen | 3 |
| Which element? | [Ne] 3s² 3p³ | P or phosphorus |
| Concept | Electrons in a d subshell? | A, B, C or D |
Tips
- Type formulas with normal capitals and numbers, e.g. Ca(OH)2 or CuSO4·5H2O – brackets and hydrates work.
- Atomic masses are IUPAC standard atomic weights; radioactive elements use the mass number of their longest-lived isotope.
- Electronegativity values are on the Pauling scale.
- Everything is calculated in your browser.
Common mistakes to avoid
- Writing CO (carbon monoxide) when you mean Co (cobalt) – capitals matter.
- Forgetting to multiply the bracket contents by the subscript after the bracket.
- Mixing up atomic number (protons) and mass number (protons + neutrons).
Formula
Filling order: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p · s 2, p 6, d 10, f 14 electronsValence electrons (main group) = group number (groups 1–2) or group number − 10 (groups 13–18)Worked example
Inputs — Question type: Mixed – any type; Elements included: Up to krypton (Z 1–36); Your answer: ; Show the answer: Only after I answer correctly.
Results — Question = How many valence electrons does a neutral krypton atom (Kr, Z = 36) have?; Result = Type a whole number in “Your answer”.; Score this session = No answers yet in this session.
Key terms
- Ground state
- The lowest-energy arrangement of an atom’s electrons.
- Subshell
- A set of orbitals with the same n and l (e.g. 3d), holding up to 2(2l + 1) electrons.
- Unpaired electron
- An electron alone in an orbital; atoms with unpaired electrons are paramagnetic.
- Isoelectronic
- Having the same number of electrons, like Na⁺, Ne and F⁻ (10 each).
Frequently asked questions
How should I type a configuration?
Any common format works: 1s2 2s2 2p6, 1s^2 2s^2 2p^6, 1s² 2s² 2p⁶ or [Ne] 3s2 3p4. Spaces are optional and the order of subshells does not matter.
Does the quiz accept the noble-gas shorthand for full-configuration questions?
Yes – the electron counts are compared, so [Ar] 4s1 is accepted for potassium. For shorthand questions the full form is accepted too.
What happens if I write the Aufbau prediction for chromium or copper?
It is marked wrong, with a note that the element is an exception: chromium is [Ar] 3d⁵ 4s¹ and copper [Ar] 3d¹⁰ 4s¹.
How are ion configurations checked?
Electrons are removed from the highest shell first, so Fe²⁺ must be [Ar] 3d⁶ and Cu⁺ [Ar] 3d¹⁰. Anions add electrons: Cl⁻ is [Ne] 3s² 3p⁶.
How is the score counted?
Each question counts once. It scores as correct if you get it right before showing the answer; retyping after a wrong attempt is allowed. The score is kept only while the page is open.
Which range should I start with?
Start with Z 1–20, where every element follows the simple rule, then move to Z 1–36 to practise the 3d series and the Cr and Cu exceptions.
What formula does the Electron Configuration Quiz use?
Filling order: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p · s 2, p 6, d 10, f 14 electrons.