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