Isoelectronic Ion Flashcards: Electron Counts & Radius Ranking
Count electrons, find matching ion configurations, rank ionic radii, and repair common charge and ordering errors with 42 short chemistry flashcards.
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Practice isoelectronic ions with 42 short English flashcards. Work with familiar monatomic ground-state ions in the 10-electron [Ne] and 18-electron [Ar] groups: N³⁻, O²⁻, F⁻, Na⁺, Mg²⁺, Al³⁺, P³⁻, S²⁻, Cl⁻, K⁺, and Ca²⁺. Atomic number Z is supplied whenever counting is the task.
The cards practice ion and Z → electron count, small list → matching-configuration group or outlier, confirmed isoelectronic pair or set → qualitative radius comparison, and constrained proton/electron counts → charge or ion symbol. Short error-repair cards address sign mistakes, equal-count/equal-size confusion, incorrect groupings, reversed orders, and skipped configuration checks. A few evidence-limit questions test what this rule can establish. Answers start with the result and give a brief explanation.
The sequence starts with charge bookkeeping and unchanged nuclei, introduces the 10-electron group, then brings in the 18-electron group before interleaving comparisons, constrained inverses, and repairs. Closely related variants are separated. Numerical radii, neutral noble-gas radius comparisons, full electron-configuration derivation, transition-metal and coordination cases, molecular species, broad periodic trends, isotope drills, and full-course or exam coverage are excluded to keep each decision short and well defined. Unconstrained radius → ion identification and exhaustive reverse/permutation cards are excluded because they do not provide one clear answer.
Original questions, explanations, organization, and metadata were written with AI assistance from common scientific facts, with factual checks against Purdue’s isoelectronic glossary, Purdue’s ionic-size lesson, and NIST’s atomic-number table. The cover is an original AI-generated conceptual illustration, not a particle-count or radius-scale diagram. CC0 1.0 applies to the original deck text, organization, metadata, and cover to the extent applicable rights exist. Scientific facts are not owned; referenced works retain their own rights. No source or competitor prose, exercises, tables, or diagrams are reproduced.
An independent learning resource with no claimed curriculum or exam alignment, affiliation, or endorsement.
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Kort 1
Fråga
For a monatomic ion, how do atomic number Z and signed charge q give its electron count?
Svar
Electron count = Z − q. Use q = +2 for a 2+ ion and q = −2 for a 2− ion.
Kort 2
Fråga
When an atom forms a monatomic ion by gaining or losing electrons, what happens to its proton count?
Svar
It stays the same. Ion formation changes the electron count, not the element’s atomic number.
Kort 3
Fråga
Na⁺, Z = 11: electron count?
Svar
10 electrons. The 1+ charge means one fewer electron than the 11 protons.
Kort 4
Fråga
What does isoelectronic mean for the closed-shell monatomic ions compared here?
Svar
They have the same electron configuration. For these ground-state 10- or 18-electron ions, matching electron totals gives the matching configuration.
Kort 5
Fråga
O²⁻, Z = 8: electron count?
Svar
10 electrons. The 2− charge means two more electrons than the eight protons.
Kort 6
Fråga
A magnesium ion has 12 protons and 10 electrons. What is its signed charge?
Svar
2+. There are two more protons than electrons: 12 − 10 = +2.
Kort 7
Fråga
Cl⁻, Z = 17: electron count?
Svar
18 electrons. A 1− ion has one more electron than its proton count.
Kort 8
Fråga
O²⁻ (Z = 8) and Mg²⁺ (Z = 12) both have 10 electrons. Which has the smaller ionic radius?
Svar
Mg²⁺. With the same electron configuration, its greater proton count pulls the electron cloud closer.
Kort 9
Fråga
Al³⁺, Z = 13: electron count?
Svar
10 electrons. Subtract the positive charge: 13 − 3 = 10.
Kort 10
Fråga
Which ion has the same electron configuration as Na⁺ (Z = 11): F⁻ (Z = 9), K⁺ (Z = 19), or Ca²⁺ (Z = 20)?
Svar
F⁻. Both F⁻ and Na⁺ have 10 electrons; K⁺ and Ca²⁺ each have 18.
Kort 11
Fråga
A learner writes: “P³⁻ has 15 − 3 = 12 electrons.” With Z = 15, repair the calculation.
Svar
15 + 3 = 18 electrons. A negative charge adds electrons to the neutral count.
Kort 12
Fråga
A monatomic ion has more electrons than protons. What sign must its charge have?
Svar
Negative. The excess electrons give a net negative charge.
Kort 13
Fråga
N³⁻ (Z = 7) and Na⁺ (Z = 11) both have 10 electrons. Which has the larger ionic radius?
Svar
N³⁻. Its smaller proton count holds the same electron configuration less tightly.
Kort 14
Fråga
N³⁻, Z = 7: electron count?
Svar
10 electrons. Add three for the 3− charge: 7 + 3 = 10.
Kort 15
Fråga
Does the isoelectronic radius rule justify ranking F⁻ (Z = 9) and Cl⁻ (Z = 17) by proton count alone?
Svar
No. F⁻ has 10 electrons and Cl⁻ has 18, so their configurations differ. This rule alone does not establish their order.
Kort 16
Fråga
Which aluminium ion has 13 protons and 10 electrons? Give its symbol and charge.
Svar
Al³⁺. The three-electron deficit gives a 3+ charge.
Kort 17
Fråga
All three ions have 10 electrons. Rank O²⁻ (Z = 8), Mg²⁺ (Z = 12), and F⁻ (Z = 9) by increasing ionic radius.
Svar
Mg²⁺ < F⁻ < O²⁻. Increasing radius follows decreasing proton count within this series.
Kort 18
Fråga
S²⁻, Z = 16: electron count?
Svar
18 electrons. Add two for the 2− charge: 16 + 2 = 18.
Kort 19
Fråga
A learner says Na⁺ (Z = 11) and Al³⁺ (Z = 13) have equal radii because both have 10 electrons. Repair the conclusion.
Svar
Al³⁺ has the smaller radius. Equal electron configurations do not mean equal sizes; Al³⁺ has the greater nuclear charge.
Kort 20
Fråga
Which ions form the 18-electron group: P³⁻ (Z = 15), Mg²⁺ (Z = 12), Cl⁻ (Z = 17), and S²⁻ (Z = 16)?
Svar
P³⁻, Cl⁻, and S²⁻. Each has 18 electrons; Mg²⁺ has 10.
Kort 21
Fråga
O²⁻ (Z = 8) and F⁻ (Z = 9) both have 10 electrons. Which has the larger ionic radius?
Svar
O²⁻. Its eight protons attract the same electron configuration less strongly than the nine protons in F⁻.
Kort 22
Fråga
A phosphorus ion has 15 protons and 18 electrons. What is its signed charge?
Svar
3−. Three excess electrons give a charge of −3.
Kort 23
Fråga
For 10-electron ions, a learner gives this increasing-radius order: N³⁻ < Na⁺ < Al³⁺. Z values are 7, 11, and 13. Repair the order.
Svar
Al³⁺ < Na⁺ < N³⁻. The greatest proton count gives the smallest radius in this series.
Kort 24
Fråga
Ca²⁺, Z = 20: electron count?
Svar
18 electrons. Subtract two for the 2+ charge: 20 − 2 = 18.
Kort 25
Fråga
Do an ion’s proton and electron counts give its exact ionic radius in picometres?
Svar
No. They support a qualitative comparison within a matching-configuration series, not an exact radius value.
Kort 26
Fråga
K⁺ (Z = 19) and Ca²⁺ (Z = 20) both have 18 electrons. Which has the smaller ionic radius?
Svar
Ca²⁺. Its extra proton attracts the same electron configuration more strongly.
Kort 27
Fråga
A learner groups F⁻ (Z = 9) with Cl⁻ (Z = 17) as isoelectronic because both are 1−. Repair the grouping claim.
Svar
They are not isoelectronic. F⁻ has 10 electrons and Cl⁻ has 18; the same ionic charge does not guarantee the same configuration.
Kort 28
Fråga
A sulfur ion has 16 protons and 18 electrons. What is its signed charge?
Svar
2−. It has two more electrons than protons.
Kort 29
Fråga
All three ions have 18 electrons. Rank Cl⁻ (Z = 17), S²⁻ (Z = 16), and Ca²⁺ (Z = 20) by increasing ionic radius.
Svar
Ca²⁺ < Cl⁻ < S²⁻. Within the shared configuration, radius increases as proton count decreases.
Kort 30
Fråga
K⁺, Z = 19: electron count?
Svar
18 electrons. A 1+ charge removes one electron from the neutral count.
Kort 31
Fråga
A learner says Mg²⁺ has 12 electrons because magnesium keeps its 12 protons when it ionizes. Repair the electron count.
Svar
10 electrons. The 12 protons stay, while a 2+ charge means two fewer electrons.
Kort 32
Fråga
Which nitrogen ion has 7 protons and 10 electrons? Give its symbol and charge.
Svar
N³⁻. Three excess electrons give a 3− charge.
Kort 33
Fråga
Are N³⁻ (Z = 7) and F⁻ (Z = 9) isoelectronic in their ground states?
Svar
Yes. Each has 10 electrons and the same closed-shell configuration.
Kort 34
Fråga
All three ions have 18 electrons. Rank S²⁻ (Z = 16), K⁺ (Z = 19), and P³⁻ (Z = 15) by decreasing ionic radius.
Svar
P³⁻ > S²⁻ > K⁺. Within this series, the ion with the fewest protons has the largest radius.
Kort 35
Fråga
A calcium ion has 20 protons and 18 electrons. A learner labels it Ca²⁻. Repair the charge sign.
Svar
Ca²⁺. The ion has two more protons than electrons, so the charge is positive.
Kort 36
Fråga
Can you apply the isoelectronic radius rule to Mg²⁺ (Z = 12) and Ca²⁺ (Z = 20) just because both have charge 2+?
Svar
No. Mg²⁺ has 10 electrons and Ca²⁺ has 18. A different comparison is needed; sharing a charge does not make this rule applicable.
Kort 37
Fråga
Which ion breaks the 10-electron group: O²⁻ (Z = 8), Ca²⁺ (Z = 20), F⁻ (Z = 9), or Mg²⁺ (Z = 12)?
Svar
Ca²⁺. It has 18 electrons; the other three each have 10.
Kort 38
Fråga
A chlorine ion has 17 protons and 18 electrons. What is its signed charge?
Svar
1−. One excess electron gives a charge of −1.
Kort 39
Fråga
A learner says O²⁻ is smaller than F⁻ because it is more negative. Both have 10 electrons; Z is 8 for O and 9 for F. Repair the comparison.
Svar
O²⁻ is larger. Within the same configuration, its smaller proton count gives a weaker nuclear pull and a larger electron cloud.
Kort 40
Fråga
Al³⁺ (Z = 13) and Mg²⁺ (Z = 12) both have 10 electrons. Which has the smaller ionic radius?
Svar
Al³⁺. It has more protons pulling on the same electron configuration.
Kort 41
Fråga
A solution ranks S²⁻ (Z = 16) and Na⁺ (Z = 11) by proton count alone. Which required check was skipped?
Svar
Whether the electron configurations match. S²⁻ has 18 electrons and Na⁺ has 10, so the isoelectronic radius rule cannot justify that ranking.
Kort 42
Fråga
Can a qualitative ionic-radius rank, with no element, charge, or candidate list, uniquely identify an ion?
Svar
No. A size rank alone does not fix an element or charge. Identification needs further constraints, such as proton and electron counts.
42 kort
Isoelectronic Ion Flashcards: Electron Counts & Radius Ranking
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