Discover the Largest Ion in an Isoelectronic Series: S2-, Cl-, K+, and Ca2+

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Discussion Overview

The discussion revolves around identifying the largest ion in the isoelectronic series consisting of S2-, Cl-, K+, and Ca2+. Participants explore concepts related to atomic size, periodic trends, and the implications of being isoelectronic.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions the relevance of the term "isoelectronic series" to the problem.
  • Another participant explains that isoelectronic ions have the same number of electrons, with variations in nuclear charge affecting size.
  • A participant notes that typically, cations are smaller than anions in an isoelectronic series due to differences in proton number and effective nuclear charge.
  • There is a reference to previous contributions from other participants regarding the comparison of radii among isoelectronic ions.

Areas of Agreement / Disagreement

Participants express varying levels of understanding about isoelectronic series and atomic size trends, with no consensus on which ion is the largest or how to approach the problem.

Contextual Notes

Participants mention the need to consider effective nuclear charge and proton number, but do not resolve how these factors quantitatively affect the size of the ions in question.

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15. The following ions comprise an isoelectronic series: S2, Cl, K+, and Ca2+
Which is the largest ion?

A. S2-
B. Cl-
C. K+
D. Ca2+
E. All should be the same size.

Don't even know what one is.
 
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What are your periodic trends for atomic size?
 
Atomic radius increases to the left and down.
 
Does the term "isoelectronic series" do anything for this problem?
 
It just means that all ions have exactly the same number of electrons, the only thing that changes is nucleus charge.
 
Last edited by a moderator:
It quite self-explanatory, atoms with the same number of electrons. You should be able to figure out the electron number in a neutral atom of the element, and further deduce the electron number of a corresponding ion.

In reference to the size of each of these, you'll need to consider the relative proton number with the electron number, effective nuclear charge. Typically, a isoelectronic cation is smaller than the anion because you've got the same number of electrons for both with a smaller proton number for the latter.
 
Not to blow any trumpets here but this essentially summarizes what has been said above by Borek and GenChemTutor, about comparing radii among isoelectronic ions.
 

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