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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Kadi namba 1
Swali
For a monatomic ion, how do atomic number Z and signed charge q give its electron count?
Jibu
Electron count = Z − q. Use q = +2 for a 2+ ion and q = −2 for a 2− ion.
Kadi namba 2
Swali
When an atom forms a monatomic ion by gaining or losing electrons, what happens to its proton count?
Jibu
It stays the same. Ion formation changes the electron count, not the element’s atomic number.
Kadi namba 3
Swali
Na⁺, Z = 11: electron count?
Jibu
10 electrons. The 1+ charge means one fewer electron than the 11 protons.
Kadi namba 4
Swali
What does isoelectronic mean for the closed-shell monatomic ions compared here?
Jibu
They have the same electron configuration. For these ground-state 10- or 18-electron ions, matching electron totals gives the matching configuration.
Kadi namba 5
Swali
O²⁻, Z = 8: electron count?
Jibu
10 electrons. The 2− charge means two more electrons than the eight protons.
Kadi namba 6
Swali
A magnesium ion has 12 protons and 10 electrons. What is its signed charge?
Jibu
2+. There are two more protons than electrons: 12 − 10 = +2.
Kadi namba 7
Swali
Cl⁻, Z = 17: electron count?
Jibu
18 electrons. A 1− ion has one more electron than its proton count.
Kadi namba 8
Swali
O²⁻ (Z = 8) and Mg²⁺ (Z = 12) both have 10 electrons. Which has the smaller ionic radius?
Jibu
Mg²⁺. With the same electron configuration, its greater proton count pulls the electron cloud closer.
Kadi namba 9
Swali
Al³⁺, Z = 13: electron count?
Jibu
10 electrons. Subtract the positive charge: 13 − 3 = 10.
Kadi namba 10
Swali
Which ion has the same electron configuration as Na⁺ (Z = 11): F⁻ (Z = 9), K⁺ (Z = 19), or Ca²⁺ (Z = 20)?
Jibu
F⁻. Both F⁻ and Na⁺ have 10 electrons; K⁺ and Ca²⁺ each have 18.
Kadi namba 11
Swali
A learner writes: “P³⁻ has 15 − 3 = 12 electrons.” With Z = 15, repair the calculation.
Jibu
15 + 3 = 18 electrons. A negative charge adds electrons to the neutral count.
Kadi namba 12
Swali
A monatomic ion has more electrons than protons. What sign must its charge have?
Jibu
Negative. The excess electrons give a net negative charge.
Kadi namba 13
Swali
N³⁻ (Z = 7) and Na⁺ (Z = 11) both have 10 electrons. Which has the larger ionic radius?
Jibu
N³⁻. Its smaller proton count holds the same electron configuration less tightly.
Kadi namba 14
Swali
N³⁻, Z = 7: electron count?
Jibu
10 electrons. Add three for the 3− charge: 7 + 3 = 10.
Kadi namba 15
Swali
Does the isoelectronic radius rule justify ranking F⁻ (Z = 9) and Cl⁻ (Z = 17) by proton count alone?
Jibu
No. F⁻ has 10 electrons and Cl⁻ has 18, so their configurations differ. This rule alone does not establish their order.
Kadi namba 16
Swali
Which aluminium ion has 13 protons and 10 electrons? Give its symbol and charge.
Jibu
Al³⁺. The three-electron deficit gives a 3+ charge.
Kadi namba 17
Swali
All three ions have 10 electrons. Rank O²⁻ (Z = 8), Mg²⁺ (Z = 12), and F⁻ (Z = 9) by increasing ionic radius.
Jibu
Mg²⁺ < F⁻ < O²⁻. Increasing radius follows decreasing proton count within this series.
Kadi namba 18
Swali
S²⁻, Z = 16: electron count?
Jibu
18 electrons. Add two for the 2− charge: 16 + 2 = 18.
Kadi namba 19
Swali
A learner says Na⁺ (Z = 11) and Al³⁺ (Z = 13) have equal radii because both have 10 electrons. Repair the conclusion.
Jibu
Al³⁺ has the smaller radius. Equal electron configurations do not mean equal sizes; Al³⁺ has the greater nuclear charge.
Kadi namba 20
Swali
Which ions form the 18-electron group: P³⁻ (Z = 15), Mg²⁺ (Z = 12), Cl⁻ (Z = 17), and S²⁻ (Z = 16)?
Jibu
P³⁻, Cl⁻, and S²⁻. Each has 18 electrons; Mg²⁺ has 10.
Kadi namba 21
Swali
O²⁻ (Z = 8) and F⁻ (Z = 9) both have 10 electrons. Which has the larger ionic radius?
Jibu
O²⁻. Its eight protons attract the same electron configuration less strongly than the nine protons in F⁻.
Kadi namba 22
Swali
A phosphorus ion has 15 protons and 18 electrons. What is its signed charge?
Jibu
3−. Three excess electrons give a charge of −3.
Kadi namba 23
Swali
For 10-electron ions, a learner gives this increasing-radius order: N³⁻ < Na⁺ < Al³⁺. Z values are 7, 11, and 13. Repair the order.
Jibu
Al³⁺ < Na⁺ < N³⁻. The greatest proton count gives the smallest radius in this series.
Kadi namba 24
Swali
Ca²⁺, Z = 20: electron count?
Jibu
18 electrons. Subtract two for the 2+ charge: 20 − 2 = 18.
Kadi namba 25
Swali
Do an ion’s proton and electron counts give its exact ionic radius in picometres?
Jibu
No. They support a qualitative comparison within a matching-configuration series, not an exact radius value.
Kadi namba 26
Swali
K⁺ (Z = 19) and Ca²⁺ (Z = 20) both have 18 electrons. Which has the smaller ionic radius?
Jibu
Ca²⁺. Its extra proton attracts the same electron configuration more strongly.
Kadi namba 27
Swali
A learner groups F⁻ (Z = 9) with Cl⁻ (Z = 17) as isoelectronic because both are 1−. Repair the grouping claim.
Jibu
They are not isoelectronic. F⁻ has 10 electrons and Cl⁻ has 18; the same ionic charge does not guarantee the same configuration.
Kadi namba 28
Swali
A sulfur ion has 16 protons and 18 electrons. What is its signed charge?
Jibu
2−. It has two more electrons than protons.
Kadi namba 29
Swali
All three ions have 18 electrons. Rank Cl⁻ (Z = 17), S²⁻ (Z = 16), and Ca²⁺ (Z = 20) by increasing ionic radius.
Jibu
Ca²⁺ < Cl⁻ < S²⁻. Within the shared configuration, radius increases as proton count decreases.
Kadi namba 30
Swali
K⁺, Z = 19: electron count?
Jibu
18 electrons. A 1+ charge removes one electron from the neutral count.
Kadi namba 31
Swali
A learner says Mg²⁺ has 12 electrons because magnesium keeps its 12 protons when it ionizes. Repair the electron count.
Jibu
10 electrons. The 12 protons stay, while a 2+ charge means two fewer electrons.
Kadi namba 32
Swali
Which nitrogen ion has 7 protons and 10 electrons? Give its symbol and charge.
Jibu
N³⁻. Three excess electrons give a 3− charge.
Kadi namba 33
Swali
Are N³⁻ (Z = 7) and F⁻ (Z = 9) isoelectronic in their ground states?
Jibu
Yes. Each has 10 electrons and the same closed-shell configuration.
Kadi namba 34
Swali
All three ions have 18 electrons. Rank S²⁻ (Z = 16), K⁺ (Z = 19), and P³⁻ (Z = 15) by decreasing ionic radius.
Jibu
P³⁻ > S²⁻ > K⁺. Within this series, the ion with the fewest protons has the largest radius.
Kadi namba 35
Swali
A calcium ion has 20 protons and 18 electrons. A learner labels it Ca²⁻. Repair the charge sign.
Jibu
Ca²⁺. The ion has two more protons than electrons, so the charge is positive.
Kadi namba 36
Swali
Can you apply the isoelectronic radius rule to Mg²⁺ (Z = 12) and Ca²⁺ (Z = 20) just because both have charge 2+?
Jibu
No. Mg²⁺ has 10 electrons and Ca²⁺ has 18. A different comparison is needed; sharing a charge does not make this rule applicable.
Kadi namba 37
Swali
Which ion breaks the 10-electron group: O²⁻ (Z = 8), Ca²⁺ (Z = 20), F⁻ (Z = 9), or Mg²⁺ (Z = 12)?
Jibu
Ca²⁺. It has 18 electrons; the other three each have 10.
Kadi namba 38
Swali
A chlorine ion has 17 protons and 18 electrons. What is its signed charge?
Jibu
1−. One excess electron gives a charge of −1.
Kadi namba 39
Swali
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.
Jibu
O²⁻ is larger. Within the same configuration, its smaller proton count gives a weaker nuclear pull and a larger electron cloud.
Kadi namba 40
Swali
Al³⁺ (Z = 13) and Mg²⁺ (Z = 12) both have 10 electrons. Which has the smaller ionic radius?
Jibu
Al³⁺. It has more protons pulling on the same electron configuration.
Kadi namba 41
Swali
A solution ranks S²⁻ (Z = 16) and Na⁺ (Z = 11) by proton count alone. Which required check was skipped?
Jibu
Whether the electron configurations match. S²⁻ has 18 electrons and Na⁺ has 10, so the isoelectronic radius rule cannot justify that ranking.
Kadi namba 42
Swali
Can a qualitative ionic-radius rank, with no element, charge, or candidate list, uniquely identify an ion?
Jibu
No. A size rank alone does not fix an element or charge. Identification needs further constraints, such as proton and electron counts.
kadi 42
Isoelectronic Ion Flashcards: Electron Counts & Radius Ranking
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