One of the simplest and best known kinds of crystals is ionic salt, of

Question

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Passage # 111, Date: 26-May-2020
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One of the simplest and best known kinds of crystals is ionic salt, of which a typical example is sodium chloride, or ordinary table salt. The fundamental components of an ionic salt are ions: atoms or molecules that have become electrically charged by gaining or losing one or more electrons. In forming sodium chloride. For example, sodium atoms give up an electron (thereby becoming positively charged) and chlorine atoms gain an electron (thereby becoming negatively charged). The ions are attracted to one another by their opposite charges, and they stack together compactly like tightly packed spheres.

Recently, scientists at Michigan State University created a new kind of crystal called an electride. In electrides, the anions (negative ions) are completely replaced by electrons, which are trapped in naturally formed cavities within a framework of regularly stacked cations (positive ions). Electrides are the first examples of ionic salts in which all these anionic sites are occupied solely by electrons.

Unlike other types of anions, anionic electrons do not behave as if they were simple charged spheres. In particular, because of their low mass and their tendency to interact with one another over great distances, they cannot be "pinned down" to any one location. Instead, they wander close to and among the atoms lining the cavity and interact with electrons in nearby cavities, perhaps changing places with them.

The properties of an electride depend largely on the distance between the cavities that hold trapped electrons. When the trapped electrons are far apart, they do not interact strongly, and so behave somewhat like an array of isolated negative charges. When they are closer together, they begin to display properties associated with large ensembles of identical particles. When they are still closer, the ensemble properties dominate and the electrons "delocalize": they are no longer tightly bound within individual cavities but are more or less free to pass through the spaces within the framework of positive ions.

By synthesizing electrides from a variety of materials, one can vary the geometry of the anionic cavities and their relation to the surrounding cations. The resulting properties may make it possible for electrides become a basis for economically useful new materials and devices. For instance, because the electrons income electrides are very weakly bound, these crystals could be effective as photosensitive detectors, in which can impinging photon liberates an electron, resulting in a small electric current. The same weak binding could also make electrides useful in solar-energy converters and as cathodes in batteries. One obstacle is the tendency of electrides to decompose through reaction with air and water. Researchers are seeking ways to increase their stability.   1 
 B 
 1. The passage is primarily concerned with discussing

A. a way to isolate electrons
B. The characteristics of a new kind of crystal
C. The structure of ionic salt crystals
D. the process of electride synthesis
E. the outcome of research in salt chemistry

2 
 E 
 2. In the first paragraph, the author is primarily concerned with

A. introducing a variant on the standard atomic theory
B. describing how chlorine atoms can become negatively charged
C. distinguishing between electrides and other ionic salts
D. presenting the identifying properties of an electride
E. providing background for the technical discussion to follow

3 
 E 
 3. According to the passage, the defining characteristic of an electride is which of the following? 
A. Its positive ions are of particularly low mass.
B. Its ions possess identical electrical stacked ions.
C. It contains a framework of regularly stacked ions.
D. Its ions demonstrate strong mutual attraction.
E. Its negative ions consist solely of electrons.

4 
 E 
 4. It can be inferred from the passage that anion behaving as "simple charged spheres’ could be expected to

A. readily lose electrons and become positively charged
B. move freely in and out of their cavities
C. respond to photons by liberating electrons
D. stack with other anions to create a regular framework
E. remain fixed relative to their cations

5 
 D 
 5. It can be inferred from the passage that an electride behaves most like a normal ionic crystal when the electride has which of the following features?

A. The anionic cavities are widely separated.
B. All of the trapped electrons are able to delocalize.
C. The trapped electrons are liberated by impinging photons.
D. The ions are tightly packed together.
E. Most of the cations have lost their electrical charge.

Sejal16 · Answer

Please explain the answer to Q1 ?

globaldesi · Answer

Official solution
1. OA: B

Tag: Big Picture

The passage discusses crystals - more specifically a new kind of crystal called electride.

Option B is most apt.

A: no focus on isolating electrons provide
B: Yes
C: 'ionic salt crystals' is too broad. The passage does not do this
D: The process itself is not described in the passage.
E: 'research in the field of salt chemistry' is too broad.

2. OA: E
Tag: Inference
The passage discusses crystals in general in the first paragraph and delves deeper into a particular kind of crystal in the following paragraphs. Option E is therefore apt.

A: No variant is discussed
B: This is not the primary concern of the first paragraph
C: The first paragraph does not talk about electrides at all.
D: The first paragraph does not talk about electride identifying qualities
3. OA: E
Tag: anchor phrase

The scope for this question is in the second paragraph
”Electrides are the first examples of ionic salts in which all these anionic sites are occupied solely by electrons.”

4. OA: E
Tag: inference
The second paragraph discusses this. The complementary information here is that these simple charged spheres are unlike anionic electrons that are "pinned down" to any one location. Therefore these simple charged spheres are NOT pinned down in one location.

A: Not supported by the passage
B: The opposite of this is true
C: Not true
D: Don't know can't say

5. OA: D

Tag: inference
The 4th paragraph contains proof for this.
” When they are still closer, the ensemble properties dominate and the electrons "delocalize": they are no longer tightly bound...” This substantiates option D.

Subash22 · Answer

Please post explanation for Q5

Gowtham91 · Answer

Hi  Subash22 ,

Explanation for Q5.

In para1 author decsribes simple ionic salts as "The ions are attracted to one another by their opposite charges, and they stack together compactly like tightly packed spheres."

In para3 author describes the difference between anions (ionic salts) and anionic electrons (electrides) as "Instead, they wander close to and among the atoms lining the cavity and interact with electrons in nearby cavities, perhaps changing places with them." From this, we can infer that anionic electrons are not closely packed as they can move freely.

from the above 2 reference from passage, we can arrive at  Option D  The ions are tightly packed together.

Other options

A. The anionic cavities are widely separated.
 
This is misleading option. From para4, "The properties of an electride depend largely on the distance between the cavities that hold trapped electrons". So this says the  distance between the cavities that hold the electrons  and not cavities itself. This means the distance between cavities in both simple ions and electrides is the same, but the distance between cavities that hold the anionic electrons (say 10 out of 100 cavities only hold the electrons) is what differentiates between the two.

B. All of the trapped electrons are able to delocalize. - This is not true for simple ions but rather for electrides.

C. The trapped electrons are liberated by impinging photons. Same explanation as option B

E. Most of the cations have lost their electrical charge. - Out of context/ irrelevant.

skhemani · Answer

Hi,

Can anyone please explain Q5. I read the given explanation here. Regular iconic salts - "The ions are attracted to one another by their opposite charges, and they stack together compactly like tightly packed spheres."

Difference between anions (ionic salts) and anionic electrons (electrodes): "Instead, they wander close to and among the atoms lining the cavity and interact with electrons in nearby cavities, perhaps changing places with them."

So, for electrides to behave as regular ionic salt, the electrons should sit tightly and close to the +ve ions (cations) and not move. However as per the passage:
"When they are still closer, the ensemble properties dominate and the electrons "delocalize": they are no longer tightly bound within individual cavities but are more or less free to pass through the spaces within the framework of positive ions."
Here "they" refer to cavity holding the electrons. There is no mention of what happens when ions of electrides are tightly packed. If from the above line of passage, we consider that the electron cavity being closer also refers to ions being closer, even then, the passage says, in such case, the electrons "delocalize".

Can anyone please explain.

Thanks

Subash22 · Answer

The two relevant references from the passage are
1. "The ions are attracted to one another by their opposite charges, and they stack together compactly like tightly packed spheres." in 1st paragraph
2. "When the trapped electrons are far apart, they do not interact strongly, and so behave somewhat like an array of isolated negative charges. When they are closer together, they begin to display properties associated with large ensembles of identical particles. When they are still closer, the ensemble properties dominate and the electrons "delocalize": they are no longer tightly bound within individual cavities but are more or less free to pass through the spaces within the framework of positive ions." in 4th paragraph
So we are looking for a feature which will make an electride behave like a normal ionic crystal, which means" they stack together compactly like tightly packed spheres"
Going to options,
A. The anionic cavities are widely separated. -This is the opposite of what we are looking for which is "tightly packed spheres". I think this is a trick option. I fell for it when I solved it the first time."When the trapped electrons are far apart," implies that the cations are also far apart. "behave like an array of isolated negative charges" This is not the behavior of a normal ionic cyrstal.
B. All of the trapped electrons are able to delocalize.- Does not say anything about the compactness of the ions. Irrelevant
C. The trapped electrons are liberated by impinging photons. -Irrelevant
D. The ions are tightly packed together. "When they are still closer, the ensemble properties dominate and the electrons "delocalize": they are no longer tightly bound within individual cavities but are more or less free to pass through the spaces within the framework of positive ions" implies that the electrons are free to move within the framework of positive ions, but not outside this framework. "When they are closer together" implies that the ions are tightly packed together. This is the closest to the feature we are looking for. 
E. Most of the cations have lost their electrical charge.- Irrelevant.
Hope this helps.

AOBang · Answer

Let me share my confusion

Between 'ionic salt' and 'electrides', the only difference is -  anions  in ionic salts are replaced with  electrons  in electrides... (agree ?)

For iconic salt >> "The ions are attracted to one another by their opposite charges, and they stack together compactly like tightly packed spheres."
 i.e they are closely packed to avoiding any relative motions of 'anions'  ... (agree?)

In electrons >> this is only possible when "the trapped electrons are far apart, they do not interact strongly, and so behave somewhat like an array of isolated negative charges."  i.e avoiding any relative motions of 'electron'.

So, option A. The anionic cavities are widely separated.

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One of the simplest and best known kinds of crystals is ionic salt, of

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