Elements—This article provides a great opportunity for students to learn about the elements that make up their world—and why they’re important.
Rare earth elements—This article shows students practical uses for these elements with the strange-sounding names.
Lanthanides/Lanthanoids—This group of elements usually seems rather generic and useless, but the article shows their criticality to our technological world.
Periodic Table—The lanthanoids are just one of many groups of elements on the periodic table with similar properties; the potassium ion exchange for sodium in glass is an example of family members on the periodic table acting similarly.
Amorphous vs. crystalline substances—Glass is an amorphous substance, while ceramics are crystalline; these examples provide an opportunity to discuss these two types of solids.
Covalent and ionic bonding—Glass contains primarily covalent bonds, with some ionic bonds also, while ceramics contain primarily ionic bonds, perhaps with some covalent bonds also.
Electron flow—Both resistive and capacitive touchscreens depend on the flow of electrons to complete electrical circuits that result in actions on the screen.
Phases of matter—Although molecules in glass are arranged in no particular order, like a liquid, they are frozen in place, like a solid; glass is a solid, NOT a liquid.
Properties of matter—Both physical and chemical properties are relevant here (e.g., metals are good electrical conductors, glass is an electrical insulator; glass is hard but brittle; glass is amorphous, ceramics are crystalline.
Possible Student Misconceptions
(to aid teacher in addressing misconceptions)
“There are lots of other materials available that we can use to substitute for the rare earth elements in smartphones and our other electronic technology.” As discussed in the “More on substitutes for the rare earth elements” above, many rare earth elements have NO substitutes, and others have substitutes that work only poorly, compared to the “real thing”.
“I’ve heard that glass is a liquid, so glass flows.”Glass is not a liquid but an amorphous solid. Because glass is often discussed in terms of its similarity to liquids, many people still believe the old tale that “glass flows,” especially in very old windows (think, ancient cathedrals) where the bottom of the panes seem thicker than the tops. Glass is, in fact, made up of molecules that are tightly held by their chemical bonds. The panes that seem thicker at the bottom were probably made that way in the early days of flat glass manufacturing.
“Glass is glass; it’s all the same.”Glass is such a common substance in our environment that we do not often consider its range of properties and, therefore, differences in different types of glass. See “More on glass” above for a list of types of glass.
“I don’t understand why they don’t make smartphone displays out of plastic—plastics in smartphones wouldn’t shatter when they hit the ground.”Although plastics don’t break, they are not as clear as glass, which would result in a “fuzzier” screen display, and they are easily scratched, which would greatly add to the “fuzziness” of the display.
Anticipating Student Questions
(answers to questions students might ask in class)
“What are the specific uses of the rare earth elements (in smartphones)?”
Here are a few specific uses for rare earth elements in smartphones:
praseodymium, gadolinium and neodymium are used in alloys in the magnets in the speaker and microphone of the smartphone
neodymium, terbium and dysprosium are used in the vibration unit of the smartphone
praseodymium and neodymium are used in glass (e.g., television screens) to reduce glare
cerium (oxide) is used to polish glass, and to extract color from colored glass
europium and yttrium (oxides) produce the red colors in television screens (and smartphone screens?)
“Why are the rare earth elements called ‘rare’ if they aren’t all that rare?” The article explains that, although they are not all that rare, they are difficult to mine and produce because they are so widely dispersed within the earth’s crust; they don’t exist in “pockets” or areas of increased concentration, as do other elements like iron, copper and silver.
“I’ve heard that the new iPhone will have a display made of sapphire, true?”Sapphire is much harder than Gorilla Glass (a Moh scale of 9 for sapphire—corundum, the second-hardest substance, after diamond—vs. about 7 for Gorilla Glass), so from that standpoint, it does not scratch as easily as Gorilla Glass, a definite “plus”. But the increased hardness also makes it brittle, so it would be all that much more likely to break when the smartphone is dropped, a definite “minus”. So, it’s unlikely we’ll see a display made of a sheet of sapphire. The most likely scenario for using sapphire is to attach a coating of sapphire powder (aluminum oxide) onto another matrix to give it support and flexibility. They’re working on this.