Video Transcript
Which of the following types of structure is formed when anions and cations bond together? A) Alternating layers of cations and anions. B) Interacting clusters of cations and anions. C) A lattice of neutral atoms. D) A lattice of alternating cations and anions. Or E) interacting clusters of neutral atoms.
Let’s start with a quick recap of what anions and cations are. Anions are negatively charged ions, like the chloride ion. Cations are positively charged ions, like the sodium ion. Anions and cations can be multiply negatively charged or positively charged. However, in this example, I’m gonna focus on ions with single charges. The magnitude of the charge does not affect the outcome.
So, how do these ions interact with one another? Anions and cations follow the principle that opposites attract and likes repel. So, if we have four ions like this, the positively charged cations and the negatively charged anions will attract one another. The anions will repel one another, and so will the cations. So, the question is, which structure has the strongest attraction?
Anions and cations will naturally form whichever structure minimizes their repulsion and maximizes their attraction. So, let’s have a look at each option and draw a picture of what we’d see.
This is how alternating layers of cations and anions might appear. There would be strong repulsion within the layers but strong attraction between them. Interacting clusters of cations and anions would have strong repulsive forces within them and forces of attraction between them. While a lattice of neutral atoms would not be ionic. So, there would be no positive–negative attraction and no positive–positive or negative–negative repulsion.
Meanwhile, a lattice of alternating cations and anions would have a mixture of short-range attractive interactions and long-range repulsive interactions. Finally, interacting clusters of neutral atoms would have some unspecified interaction between the cluster of atoms with no attractive positive–negative interactions inside the clusters but no repulsive positive–positive or negative–negative repulsions.
C and E can automatically be eliminated because anions and cations are not suddenly going to give up or gain electrons, unless they’re highly unstable. In the alternating layers of cations and anions, option A, there is nothing holding the layers together. There are only repulsive interactions. Therefore, this would not be stable. Therefore, this is not a correct answer.
Meanwhile, interacting clusters of cations and anions would have nothing holding the clusters together. The ions would repel each other, and the material would explode. Therefore, this too is not a correct answer.
What about a lattice of alternating cations and anions? Here, every ion is setting up against an ion of the opposite charge, so there is a strong force of attraction. The further away two ions of the same charge are, the weaker the repulsion between them. So, in an alternating lattice of cations and anions, there is overall a weak repulsion and a strong attraction.
So, of the types of structure given, the one that forms when anions and cations bond together is a lattice of alternating cations and anions.
