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Question Video: Understanding How to Represent the Crystal Structure of an Ionic Compound Chemistry • 7th Grade

Which of the following diagrams best represents the crystal structure of an ionic compound? [A] Diagram A [B] Diagram B [C] Diagram C [D] Diagram D

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Video Transcript

Which of the following diagrams best represents the crystal structure of an ionic compound?

The question tells us that the correct diagram will represent an ionic compound, which is a compound that is composed of positively and negatively charged ions. This type of compound results when atoms transfer electrons and form ions. This behavior is explained by the octet rule of thumb, which tells us that, in general, atoms tend to lose or gain electrons to achieve an octet of valence electrons in the outermost shell. These now oppositely charged ions are attracted to each other, experiencing what is called electrostatic attraction.

The diagrams in the answer choices use these larger particles with a plus to represent positively charged ions and these smaller particles with a minus to represent negatively charged ions. And we must identify the diagram that represents what is called a crystal structure. And since we are working with an ionic compound, the crystal structure is formed due to the ionic lattice, which is a giant three-dimensional structure that is made up of oppositely charged ions. The ionic lattice occurs due to the very strong electrostatic attractions between oppositely charged ions.

These ions continue to attract other ions, with the positively charged ions attracting other negatively charged ions and the negatively charged ions attracting other positively charged ions, until there are many, many more ions in all directions. This orderly, tightly packed arrangement of alternating oppositely charged ions eventually forms the three-dimensional lattice of a crystal. However, drawing this three-dimensional lattice to represent a crystal structure is not practical. So, instead, we will often see in a diagram just one layer of the ionic lattice isolated and limited to two dimensions. So let’s compare the answer choices to our two-dimensional diagram of the crystal structure.

We can see that the best representation of a crystal structure of an ionic compound is answer choice (C).

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