Classify each compound as ionic or molecular. a. CO2 b. NiCl2 c. Nal d. PCl3

Video transcript

All right. Hi everyone. So this question is asking us of the following compounds. Part one which ones exist as molecules and two, which ones manifest as extended structures spanning three dimensions. Here we have sodium chloride, carbon dioxide, silicone dioxide and boron tr fluoride. So let's go ahead and start with sodium chloride. Now recall that sodium chloride is an ionic compound in which sodium has a positive charge and chloride has a negative charge. No, because of this opposite charge, then both ions are going to be attracted to each other via electrostatic forces. So what that does is it creates a very regular three dimensional lattice structure because if sodium is a white circle and chloride is a black circle, then this pattern creates. But this attraction creates a sort of alternating pattern. It creates a very regular alternating pattern in which two ions of the same charge never actually interact with each other forming a very regular three dimensional lattice. Therefore, sodium chloride falls under the category described in part two here because sodium chloride manifests as an extended structure spanning three dimensions because of this electrostatic attraction. Now, by contrast, right, and carbon dioxide has linear geometry in which carbon is in the center and it has two double bonds, the two atoms of oxygen. Now, because of this linear geometry, carbon dioxide is actually nonpolar and not only is it non polar and carbon dioxide exists predominantly as a gas, right. So because of this individual molecules of carbon dioxide don't form an extended structure in the gaseous state. So while carbon dioxide is a covalent molecular compound, it doesn't form an extended structure with other molecules of co two because they're in the gaseous state, right. So there's simply too much distance between them for them to create a larger structure. So carbon dioxide primarily exists as a molecule. Now, by contrast, we have silicone dioxide and silicon dioxide exists not only as a solid but as a covalent network solid, which explains why it's found in courts, for example, right, because silicon dioxide does actually form an extended three dimensional network structure in which each atom of silicone is bound to four oxygen atoms in a tetrahedral structure. So for example, right, we've got one atom of silicone in the center and it's going to be found or bound to four different atoms of oxygen which are further bound to other atoms of silicone. And so what that does is create this sort of three dimensional lattice. Therefore, silicone dioxide does manifest as an extended structure spanning three dimensions. Now, BF three on the other hand, or boron trifle is another covalent molecular compound in which an animal boron is bound to three atoms of fluorine. Now it is trigonal planar and it is therefore, or it's trigonal planar and also nonpolar. And recall also that individual molecules of boron tr fluoride do not tend to have an extended structure, meaning that they tend to retain this configuration as BF three and they don't tend to create larger three dimensional structures the way that silicone dioxide can't, right. So boron tr fluoride predominantly exists as simply BF three and not as part of a larger network and there you have it. So here is our final answer, right. Of the four compounds listed the ones that exist as molecules are carbon dioxide and boron tr fluoride. Whereas the ones that manifest as extended structures spanning three dimensions are sodium chloride and silicone dioxide. So with that being said, thank you so very much for watching. And I hope you found this helpful.