Video: Selecting the Substance That Is an Ionic Solid

Which of the following substances at room temperature is an ionic solid? [A] C (graphite) [B] MgO [C] N₂H₄ [D] CO [E] NO₂


Video Transcript

Which of the following substances at room temperature is an ionic solid? A) C, or graphite. B) MgO. C) N₂H₄. D) CO. Or E) NO₂.

An ionic solid is a type of compound that’s composed of oppositely charged ions. Ions are charged particles that form when an atom gains or loses an electron. If it has a positive charge, we call it a cation. And if it has a negative charge, we call it an anion. These ions in an ionic solid are formed because an electron is transferred between one element to another.

Though not always, it’s common to have ionic solids that are composed of a metal and a non-metal. For example, NaCl, or sodium chloride, which you probably have around your house in the form of table salt, is an example of an ionic solid. Sodium is a metal found in group one of the periodic table. And chlorine is a non-metal.

When sodium and chlorine come together to make sodium chloride, the sodium gives up one of its electrons to the chlorine so that sodium becomes a positively charged cation and that the chlorine becomes a negatively charged anion. At room temperature, this will form our ionic solid, which will be composed of the sodium cations and the chloride anions.

The covalent bond is another common bond in chemistry where electrons are shared as opposed to being transferred to form ions. Covalent bonds typically occur between non-metals, and some examples are H₂O or water, CH₄, and SF₆. Now, let’s look through our answer choices to determine which one will be an ionic solid. We’ll be looking for one that is most likely composed of a metal and a non-metal capable of forming ions.

A is C, or carbon in the form of graphite. Graphite is composed of a network of carbons. Each carbon in graphite is bound to three other carbons with covalent bonds. Carbon can form a maximum of four covalent bonds, so the carbons in graphite actually have a delocalized electron that gets spread out throughout the structure. Now, in this question, we’re looking for an ionic solid, and graphite is composed of a network of covalently bonded carbons. So, this isn’t the correct answer choice.

Answer choice B is MgO, or magnesium oxide. Magnesium is a metal that’s found in group two of the periodic table. And oxygen is a non-metal that’s found in group 16, or sometimes called group six of the periodic table. Magnesium likes to give up two of its electrons to form a cation. And oxygen can easily take those two electrons to form an anion. Magnesium oxide seems to be a pretty good fit for a description of an ionic solid as magnesium is a metal that can form a cation and oxygen is a non-metal that can form an anion. But let’s take a look at the other answer choices.

Answer choice C is N₂H₄, which is called dinitrogen tetrahydride. Both nitrogen and hydrogen are non-metals, so it’s most likely that this compound will form covalent bonds. Answer choice D is CO, which is called carbon monoxide. Carbon monoxide has a covalent bond, as carbon and oxygen are both non-metals. Answer choice E is NO₂, which is called nitrogen dioxide. Again, nitrogen and oxygen are both non-metals. This compound is bound by covalent bonds. So, as we suspected, magnesium oxide will be the substance that forms an ionic solid at room temperature.

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