April/May 2015 Teacher's Guide for Smartphones, Smart Chemistry Table of Contents

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Background Information

(teacher information)

More on the history of the rare earth elements
The first rare earth elements to be discovered were yttrium and cerium. They were discovered in minerals (in 1787 and 1794) from Sweden. Although the minerals ytterbite (now gadolinite) and cerite were newly discovered, they appeared to be composed of common elements, so it took a while until the oxides of yttrium and cerium (yttria and were isolated from them, and the new elements were discovered. By 1803, then, only these two rare earths were known.
It took more than 30 more years to determine that more rare earth elements existed within these minerals. This was due to the fact that the chemistry of the rare earths is essentially the same for all of them (see “More on the physical and chemical properties of the rare earth elements”), making separation and identification extremely difficult. Eventually, terbium and erbium were isolated from the new oxides terbia and erbia found in yttria (the oxide of yttrium), and lanthanum and didymium (not really an element, as we now know) were isolated from cerite. So, by 1842 six rare earths were known: yttrium, cerium, terbium, erbium, lanthanum and didymium (which, as it turns out, wasn’t really an element at all, but a combination of two other elements).
And there discovery languished for another 30 years, until spectroscopy matured as a scientific endeavor. The spectrum of didymia, the oxide of didymium, eventually revealed the existence of two different elements, neodymium and praseodymium and so didymium was removed from the list of elements. Around this same time, samarium was tweaked out of a mineral called samarskite. Ytterbia was extracted from erbia, and ytterbium was identified as a new element. Further purification of erbia produced the new oxides holmia and thulia, from which elements holmium and thulium were identified. Dysprosium was then isolated from holmia (which was a mixture of the oxides of holmium and dysprosium). Later, gadolinium was also isolated from samarskite. Europium was later discovered from the spectroscopic study of samarskite, samaria and yttria (oxides of these elements).
Scientists didn’t know how many rare earth elements there were, but Moseley, by 1912, using x-ray crystallography, had established the concept of the atomic number of the elements. Using this idea, scientists were able to determine that there were to be only 15 rare earths, and after the 14 mentioned above were discovered, it was observed that one element was missing, between neodymium and samarium, element number 61. It was another 30+ years before promethium would be discovered in 1947 from the fission products of the nuclear reactor at Oak Ridge.

(sources: http://www.periodni.com/history_of_rare_earth_elements.html and http://en.wikipedia.org/wiki/Rare_earth_element)

The chart below shows a graphic portrayal of the discovery of these elements, starting with the minerals cerite and ytterbite and branching out from there. Note that it somewhat resembles a family tree.

(E. Generalic, http://www.periodni.com/rare_earth_elements.html)
The table below from Wikipedia provides information on the atomic number, symbol, name, etymology and applications of the rare earth elements. Note that some of the rare earths are named after scientists involved with their discovery or understanding of their properties, and some are named after their place of discovery.





Selected applications




from Latin Scandia (Scandinavia).

Light aluminium-scandium alloys for aerospace components, additive in metal-halide lamps and mercury-vapor lamps,[4] radioactive tracing agent in oil refineries




after the village of Ytterby, Sweden, where the first rare earth ore was discovered.

Yttrium aluminium garnet (YAG) laser, yttrium vanadate (YVO4) as host for europium in TV red phosphor, YBCO high-temperature superconductors, yttria-stabilized zirconia (YSZ), yttrium iron garnet (YIG) microwave filters,[4] energy-efficient light bulbs,[5] spark plugs, gas mantles, additive to steel




from the Greek "lanthanein", meaning to be hidden.

High refractive index and alkali-resistant glass, flint, hydrogen storage, battery-electrodes, camera lenses, fluid catalytic cracking catalyst for oil refineries




after the dwarf planet Ceres, named after the Roman goddess of agriculture.

Chemical oxidizing agent, polishing powder, yellow colors in glass and ceramics, catalyst for self-cleaning ovens, fluid catalytic cracking catalyst for oil refineries, ferrocerium flints for lighters




from the Greek "prasios", meaning leek-green, and "didymos", meaning twin.

Rare-earth magnets, lasers, core material for carbon arc lighting, colorant in glasses and enamels, additive in didymium glass used in welding goggles,[4] ferrocerium firesteel (flint) products.




from the Greek "neos", meaning new, and "didymos", meaning twin.

Rare-earth magnets, lasers, violet colors in glass and ceramics, didymium glass, ceramic capacitors




after the Titan Prometheus, who brought fire to mortals.

Nuclear batteries




after mine official, Vasili Samarsky-Bykhovets.

Rare-earth magnets, lasers, neutron capture, masers




after the continent of Europe.

Red and blue phosphors, lasers, mercury-vapor lamps, fluorescent lamps, NMR relaxation agent





Selected applications




after Johan Gadolin (1760–1852), to honor his investigation of rare earths.

Rare-earth magnets, high refractive index glass or garnets, lasers, X-ray tubes, computer memories, neutron capture, MRI contrast agent, NMR relaxation agent, magnetostrictive alloys such as Galfenol, steel additive




after the village of Ytterby, Sweden.

Green phosphors, lasers, fluorescent lamps, magnetostrictive alloys such as Terfenol-D




from the Greek "dysprositos", meaning hard to get.

Rare-earth magnets, lasers, magnetostrictive alloys such as Terfenol-D




after Stockholm (in Latin, "Holmia"), native city of one of its discoverers.

Lasers, wavelength calibration standards for optical spectrophotometers, magnets




after the village of Ytterby, Sweden.

Infrared lasers, vanadium steel, fiber-optic technology




after the mythological northern land of Thule.

Portable X-ray machines, metal-halide lamps, lasers




after the village of Ytterby, Sweden.

Infrared lasers, chemical reducing agent, decoy flares, stainless steel, stress gauges, nuclear medicine




after Lutetia, the city that later became Paris.

Positron emission tomography – PET scan detectors, high-refractive-index glass, lutetium tantalate hosts for phosphors

The following abbreviations are often used:

  • RE = rare earth

  • REM = rare-earth metals

  • REE = rare-earth elements

  • REO = rare-earth oxides

  • REY = rare-earth elements and yttrium

  • LREE = light rare earth elements (Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd; also known as the cerium group)[7][8]

  • HREE = heavy rare earth elements (Y, Tb, Dy, Ho, Er, Tm, Yb, and Lu; also known as the yttrium group)[7][8]

The densities of the LREEs (as pure elements) range from 2.989 (scandium) to 7.9 g/cc (gadolinium), whereas those of the HREEs are from 8.2 to 9.8, except for yttrium (4.47) and ytterbium (between 6.9 and 7). The distinction between the groups is more to do with atomic volume and geological behavior (see lower down).


More on the rare earth elements
The International Union of Pure and Applied Chemistry is the official organization that regulates the scientific aspects of chemistry. It has issued this statement regarding the names of groups of elements on the periodic table, including the rare earth elements, as part of one of its provisional reports:
IR-3.6.2 Collective names of groups of like elements
The following collective names for groups of atoms are IUPAC-approved: alkali metals (Li, Na, K, Rb, Cs, Fr), alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra), pnictogens (N, P, As, Sb, Bi), chalcogens (O, S, Se, Te, Po), halogens (F, Cl, Br, I, At), noble gases (He, Ne, Ar, Kr, Xe, Rn), lanthanoids (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu), rare earth metals (Sc, Y and the lanthanoids), and actinoids (Ac, Th, Pa, U, Np, Pu, Am, Cm, Bk, Cf, Es, Fm, Md, No, Lr). [Emphasis added by Teacher’s Guide editor]
(http://old.iupac.org/reports/provisional/abstract04/RB-prs310804/Chap3-3.04.pdf, p 8)
This site further explains IUPAC’s position on rare earth elements:
The International Union of Pure and Applied Chemistry (IUPAC) defines rare earth elements (REE) or rare earth metals as a collection of seventeen chemical elements in the periodic table, specifically the fifteen lanthanides (Note: Even though lanthanoid means 'like lanthanum' and as such should not include lanthanum it has become included through common usage.) plus scandium and yttrium (Figure 1). Scandium and yttrium are considered rare earth elements since they tend to occur in the same ore deposits as the lanthanides and exhibit similar chemical properties.
(Generalic, E. http://www.periodni.com/rare_earth_elements.html)


The graph at right shows the abundances of the elements, compared to that of silicon. As you can see, the rare earth elements are NOT the least abundant elements (hence, rare)—although they are significantly LESS abundant than the lower atomic number, “rock-forming elements” at the left of the graph, in the aggregate approximately 100,000 times less abundant; however, they are all significantly MORE abundant than the true precious metals, in the aggregate, approximately 1000 times more abundant.

More on the physical and chemical properties of the rare earth elements
This table from Wikipedia summarizes some of the physical properties of the lanthanoids.

Note that the density of the lanthanoids generally increases across the row, as is the case for most rows of the periodic table. Also note that the metallic radius generally (although not as steadily) decreases. Since density is equal to mass divided by volume, and since mass increases slightly (greater atomic number, more protons and neutrons), as volume decreases slightly across the row, density is expected to increase across the row.
M As M increases M

D = and V decreases, = D

V D increases V
Europium and ytterbium, with half-full and full sets of f orbitals, respectively, have by far the largest metallic radii and lowest densities of all the lanthanoids. It is believed that the metal contains primarily the Eu2+ ion, with only two electrons in its conduction band (owing to the stability of its half-filled set of f orbitals). Ytterbium (with its full set of f orbitals) appears to behave similarly.
(E. Generalic, http://www.periodni.com/rare_earth_elements.html)

Note also that there appear to be two distinct groups of the lanthanoids in terms of their densities. Lanthanum through gadolinium (57–64) all have densities between 5.2 and 7.9, while terbium through lutetium (65–71) have densities between 8.2 and 9.8 (with the exception of ytterbium at 6.9). The former group, La–Gd, is referred to as the light rare earth elements (LREEs), while the latter group, Tb–Lu, is referred to as the heavy rare earth elements (HREEs). The LREEs each have only unpaired electrons in their f orbitals, while the HREEs (including yttrium) all have one or more f orbitals (the s orbital for yttrium) occupied by paired electrons.

Melting points and boiling points generally increase from left to right across the row of lanthanoids also. This is believed to be due to the extent of hybridization of the 6s, 5d and 4f orbitals. Cerium is believed to have the greatest degree of hybridization, and it has by far the lowest melting point of all the lanthanoids. Europium and ytterbium, with their half-full and full sets of f orbitals (respectively) would also be highly hybridized and therefore should (and do) have low melting points.
Hardness, although it is not one of the physical properties listed on the table above, also follows an increasing trend. All the lanthanoids are soft metals, but their hardness increases across the row.
Resistivities are relatively high for metals. Compare their numbers, roughly 30–130, to that of a good conductor of electricity—aluminum, for example, has a resistivity of 2.6.
The lanthanoids are all strongly paramagnetic, except for lanthanum, ytterbium and lutetium, which have no unpaired electrons. This is in keeping with their relatively high magnetic susceptibility readings.

Chemical properties
This table from Wikipedia summarizes a few of the chemical properties of the lanthanoids.

Chemical element
















Atomic number
















Ln3+ electron configuration*[10]
















Ln3+ radius (pm)[8]
















Note: Ln is the general abbreviation used here to represent any lanthanoid.

The lanthanoids all react to form a +3 ion (Ln3+). This is due to the hybridization of the two electrons in the 6s and (usually) one electron in the 4f orbitals that are available for bonding. Electrons in the other f orbitals typically are not involved in bonding because they reside closer to the nucleus, within inner orbitals. They penetrate the Xe core and are isolated, thus not participating in bonding. The phenomenon known as the “lanthanide contraction”, where the radius of the Ln3+ ion in the series decreases as you go from left to right across the periodic table, is thought to be due to the poor shielding provided by the 4f orbitals for the 5s and 5p orbitals. The similar hybridization in the lanthanoids goes a long way to explaining why they all have similar chemistry.


And their similar chemistry also explains in part why chemists had such a difficult time isolating them and establishing their existence as true elements. The other factor that prevented their early separation is their similar Ln3+ ionic radii in the metallic oxides in which they occur in natural ores and minerals. Chemists during the early days of research into the rare earths would find rare earth oxides, but they would miss other rare earths that existed within these ores, and only later were these other rare earths separated and “discovered”.

More on rare earths’ supply and demand today
OK, so we’ve give you a lot of information about lanthanoids, aka rare earths. But why are they so important? The table below provides a partial list of the uses for rare earth elements. For many of these applications, rare earths are the only substances that will work; substitutes are either not available, or they are far inferior to the real thing.

Table 1. Distribution of rare earths by end use.

Product groups

Fraction / %

metallurgical applications and alloys




chemical catalysts


rare-earth phosphors for computer monitors, lighting, radar, televisions, and x-ray-intensifying film


automotive catalytic converters


glass polishing and ceramics


permanent magnets


petroleum refining catalysts





The material below provides information from the U.S. Geological Survey (USGS) about the supply of and demand for the rare earth elements.
Rare Earths1
Events, Trends, and Issues: In 2014, increased domestic consumption of rare earths was stimulated by lower prices and increased availability of rare-earth compounds. Increased domestic production of separated rare-earth products was hampered by technical difficulties in the rampup of new production capacity. Despite increased global demand for rare earths in the permanent magnet and catalyst industries, prices for most rare-earth compounds declined in 2014 owing to an excess of inventory in the market. Consumption of rare-earths in the phosphor industry decreased owing to the increased use of LED lighting, which requires less rare earths than fluorescent lighting.
Global consumption of rare earths was expected to increase at a compound annual growth rate in excess of 5% from 2014 through 2020. China continued to dominate the global supply of rare earths. In 2014, China’s rare-earth export quotas were 31,000 tons, including 27,383 tons for light rare earths and 3,617 tons for heavy rare earths. In August, the World Trade Organization upheld a ruling in favor of the United States, the European Union, and Japan’s claims that China violated trade rules with respect to the unfair imposition of export restrictions on rare earths despite China’s claims that the controls were aimed at protecting the environment and conserving resources. China continued efforts to consolidate its rare-earths industry and clamp down on illegal production and exports. China’s State Bureau of Material Reserve continued to expand its stockpile of rare earths.
Rare Earths1
[Data in metric tons of rare-earth oxide (REO) equivalent content unless otherwise noted]
Domestic Production and Use: Rare earths were mined by one company in 2014. Bastnäsite, a fluorocarbonate mineral, was mined and processed into concentrates and rare-earth compounds at Mountain Pass, CA. The United States continued to be a net importer of rare-earth products in 2014. The estimated value of rare-earth metals and compounds imported by the United States in 2014 was $210 million, a decrease from $256 million imported in 2013. The estimated distribution of rare earths by end use was as follows, in decreasing order: catalysts, 60%; metallurgical applications and alloys, 10%; permanent magnets, 10%; glass polishing, 10%; and other, 10%.
Salient Statistics—United States: 2010 2011 2012 2013 2014e

Production, bastnäsite concentrates — — 3,000 5,500 7,000



Cerium compounds 1,770 1,120 1,390 1,160 1,500

Other rare earth compounds 10,500 6,020 3,900 8,080 10,000


Rare-earth metals, scandium, and yttrium 525 468 240 393 310

Ferrocerium, alloys 131 186 267 313 360



Cerium compounds 1,350 1,640 992 734 640

Other rare-earth compounds 1,690 3,620 1,830 5,570 5,600


Rare-earth metals, scandium, and yttrium 1,380 3,030 2,080 1,040 160

Ferrocerium, alloys 3,460 2,010 951 1,420 2,100

Consumption, estimated 15,000 11,000 15,000 15,000 17,000

Price, dollars per kilogram, yearend3:

Cerium oxide, 99% minimum 60–62 40–45 10–12 5–6 4–5

Dysprosium oxide, 99% minimum 285–305 1,400–1,420 600–630 440–490 320–360

Europium oxide, 99.9% minimum 620–640 3,780–3,800 1,500–1,600 950–1,000 680–730

Lanthanum oxide, 99% minimum 59–61 50–52 9–11 6 5

Mischmetal, 65% cerium, 35% lanthanum 57–60 47–49 14–16 9–10 9–10

Neodymium oxide, 99% minimum 86–89 190–200 75–80 65–70 56–60

Terbium oxide, 99% minimum 595–615 2,800–2,820 1,200–1,300 800–850 590–640

Employment, mine and mill, annual average 98 146 275 380 394

Net import reliance4 as a percentage of

estimated consumptione 100 100 80 63 59
Import Sources (2010–13): Rare-earth compounds and metals: China, 75%; France, 6%; Japan, 6%; Estonia, 4%; and other, 9%.

World Mine Production and Reserves: …
Mine productione Reserves5

2013 2014

United States 5,500 7,000 1,800,000

Australia 2,000 2,500 63,200,000

Brazil 330 — 22,000,000

China 95,000 95,000 55,000,000

India 2,900 3,000 3,100,000

Malaysia 180 200 30,000

Russia 2,500 2,500 (7)

Thailand 800 1,100 NA

Vietnam 220 200 (7)

Other countries NA NA 41,000,000
World total (rounded) 110,000 110,000 130,000,000
World Resources: Rare earths are relatively abundant in the Earth’s crust, but discovered minable concentrations are less common than for most other ores. U.S. and world resources are contained primarily in bastnäsite and monazite. Bastnäsite deposits in China and the United States constitute the largest percentage of the world’s rare earth economic resources, and monazite deposits constitute the second largest segment.
eEstimated. NA Not available. — Zero.

1Data include lanthanides and yttrium but exclude most scandium. See also Scandium and Yttrium.

2REO equivalent or contents of various materials were estimated. Source: U.S. Census Bureau.

3Price range from Metal-Pages Ltd.

4Defined as estimated consumption ‒ production. Insufficient data were available to determine stock changes and unattributed imports and exports of rare-earth materials.

5See Appendix C for resource/reserve definitions and information concerning data sources.

6For Australia, Joint Ore Reserves Committee (JORC)-compliant reserves were about 2.2 million tons.

7Included with “Other countries.”
A separate document, “Rare Earths” that contains only the two pages of data that deal with rare earths can be found here: http://minerals.usgs.gov/minerals/pubs/commodity/rare_earths/mcs-2015-raree.pdf. The source above also provides two pages of information, similar to that mentioned above, for scandium and yttrium, frequently associated or grouped with the rare earth elements.
The graph below shows the last 50 years of global production of mined rare earth elements. Note that although the U.S. was the primary producer from 1960 to 1985, China for the last 20 years has “cornered the market”, while U.S. production has dropped to almost zero (7,000 metric tons (1,000 kg/metric ton) in 2014, almost not registering on a graph of this scale). This clearly shows why all the major technologically-advanced countries of the world are so concerned about the future supply of rare earths.

It is interesting to note that, despite the ever-more critical need for rare earth elements for technology and electronics (and defense), the U.S. Government does not stockpile these materials, as it does petroleum, for example.
More on substitutes for rare earth elements
As mentioned in the article, the rare earths are difficult to find and mine because they are so “dilute” in the Earth’s crust. China’s near-monopoly of the rare earths has provided cause for concern about the continued availability of these elements for technological uses. Indeed, the use and continued availability of many metals in modern society has become a critical issue.
A metal’s life cycle tells a great deal about the current situation [of its availability] but says nothing about possible changes in supply or demand at any point in the cycle. Those aspects can be addressed to at least some degree by studies of a metal’s criticality. This concept originated in 2006 when the US National Research Council (NRC) undertook a study to address the lack of understanding and of data on nonfuel minerals important to the US economy. The report (16) defined the criticality of minerals as a function of two variables: importance of uses and availability. The NRC committee carried out preliminary criticality analyses for several metals. Of those surveyed, a number were identified as critical: rhodium, platinum, manganese, niobium, indium, and the rare earths. [Editor’s emphasis]
And no viable substitutes for these elements have been (or are likely to be) found. Yale professor Thomas Graedel has done a study of the possible substitution for various metals and metalloids presently in use and reached rather serious conclusions.
Modern life is enabled by the use of materials in its technologies. Over time, these technologies have used a larger and more diverse array of materials. Elemental life cycle analyses yield an understanding of these materials, and a definite concern that arises is that of possible scarcity of some of the elements as their use increases. We studied substitution potential for 62 different metals in their major uses. For a dozen different metals, the potential substitutes for their major uses are either inadequate or appear not to exist at all. Further, for not 1 of the 62 metals are exemplary substitutes available for all major uses.
(Graedel, T.; Harper, E.; Nassar, N.; Reck, B. On the Materials Basis of Modern Society. Proceedings of the National Academy of Sciences of the United States of America. PNAS 2013; published ahead of print December 2, 2013, doi:10.1073/pnas.1312752110; abstract from http://www.pnas.org/content/early/2013/11/27/1312752110; complete article here: http://www.pnas.org/content/early/2013/11/27/1312752110.full.pdf+html)
The periodic table below from Graedel’s study uses the color-coded scheme to illustrate the status of substitute materials for the various elements. Note the lack of blues and true greens, indicating the lack of excellent substitutes for these elements.

The Graedel article also provides online supporting information with a comprehensive, detailed table (34 pages) of those 62 elements, citing for each element: its applications in society and details thereof; the percentage of the element used in that application; the element’s primary substitute material; and the substitute’s performance. This list may be useful in your classes as you discuss metals in the curriculum, just to show students the diversity of uses for metals in today’s society.
A second supporting document contains details about how and why the study was done, as well as the periodic table from the article, and a graph showing the aggregated “ratings” of those elements vis a vis the performance of presently available substitute materials. This graph shows that not a single metal has a substitute material that performs adequately in all applications, and roughly one-fourth of these metals have substitutes that only work extremely poorly in most applications.


More on glass
The diagram below appeared in the July 29, 2008 issue of the New York Times.

glass, up close

The October 2006 ChemMatters Teacher’s Guide that accompanies the article, “Glass: More than Meets the Eye” contains much information about glass, its composition and its properties. Some is reproduced here.

More on the Composition of Glass
Because glass is used in so many different ways, there is no one chemical composition for each glass sample. There are thousands of different glass compositions. However, there are three categories of substances in all glass – formers, fluxes and stabilizers. The most common former is silicon dioxide, SiO2, in the form of sand. Other possible formers include B2O3 and P2O5. The former makes up the bulk of the glass. Fluxes change the temperature at which the formers melt during the manufacturing of glass. Substances commonly used as fluxes include sodium carbonate, Na2CO3, and potassium carbonate, K2CO3. Stabilizers strengthen the glass and make it resistant to water. Calcium carbonate, CaCO3, is the most frequently used stabilizer.
The raw materials for making glass are all oxides. So the composition of any sample of glass can be given in terms of the per cent of each oxide used to make it. For example, the glass used to make windows and bottles has the following approximate composition:

Silica – SiO2 73.6 %

Soda – Na2O 16.0 %

Lime – CaO 5.2 %

Potash – K2O 0.6 %

Magnesia – MgO 3.6 %

Alumina – Al2O3 1.0 %

Note that the magnesia and alumina are present as impurities.

According to the Corning Museum of Glass Web site (http://www.cmog.org/default.asp) [no longer accessible] there are six basic types of glass based on composition: “Nearly all commercial glasses fall into one of six basic categories or types. These categories are based on chemical composition. Within each type, except for fused silica, there are numerous distinct compositions.
Soda-lime glass is the most common (90% of glass made), and least expensive form of glass. It usually contains 60-75% silica, 12-18% soda, 5-12% lime. Resistance to high temperatures and sudden changes of temperature are not good and resistance to corrosive chemicals is only fair. Flat glass and container glass is this type.
Lead glass has a high percentage of lead oxide (between 20% and 80% of the batch). It is relatively soft, and its refractive index gives a brilliance that may be exploited by cutting. It is somewhat more expensive than soda-lime glass and is favored for electrical applications because of its excellent electrical insulating properties. Thermometer tubing and art glass are also made from lead-alkali glass, commonly called lead glass. This glass will not withstand high temperatures or sudden changes in temperature.

Borosilicate glass is any silicate glass having at least 5% of boric oxide in its composition. It has high resistance to temperature change and chemical corrosion. Not quite as convenient to fabricate as either lime or lead glass, and not as low in cost as lime, borosilicate's cost is moderate when measured against its usefulness. Pipelines, light bulbs, photochromic glasses, sealed-beam headlights, laboratory ware, and bake ware are examples of borosilicate products.

Aluminosilicate glass has aluminum oxide in its composition. It is similar to borosilicate glass but it has greater chemical durability and can withstand higher operating temperatures. Compared to borosilicate, aluminosilicates are more difficult to fabricate. When coated with an electrically conductive film, aluminosilicate glass is used as resistors for electronic circuitry.
Ninety six percent silica glass is a borosilicate glass, melted and formed by conventional means, then processed to remove almost all the non-silicate elements from the piece. By reheating to 1200°C the resulting pores are consolidated. This glass is resistant to heat shock up to 900°C. “Fused silica glass is pure silicon dioxide in the non-crystalline state. It is very difficult to fabricate, so it is the most expensive of all glasses. It can sustain operating temperatures up to 1200°C for short periods.”
More on Properties of Glass
Glass combines some properties of crystals and some of liquids but glass is distinctly different from both. Glass is rigid like a crystal but the molecules that make up glass are arranged randomly like liquids. In general glass is formed by melting crystalline substances and then cooling the liquid before the molecules can form a crystal. Glass does not have a specific melting point but softens over a range of temperatures.

According to the Corning Museum of Glass, the properties of glass include:

  • Mechanically Strong – Glass has great inherent strength and is weakened only by surface imperfections, which give everyday glass its fragile reputation. Special tempering can minimize surface flaws.

  • Hard surface – Glass resists scratches and abrasions. (Because the composition can vary, so can the hardness. On average the hardness of glass is about 5.5 on the Moh’s scale)

  • Elastic – Glass “gives” under stress – up to a breaking point – but rebounds exactly to its original shape

  • Chemical corrosion-resistant – Glass is affected by few chemicals. It resists most industrial and food acids.

  • Thermal shock-resistant – Glass withstands intense heat or cold as well as sudden temperature changes.

  • Heat-absorbent – Glass retains heat, rather than conducts it. Glass absorbs heat better than metal.

  • Optical Properties – Glass reflects, bends, transmits and absorbs light with great accuracy.

  • Electrical Insulating – Glass strongly resists electric current. It stores electricity very efficiently.

More on Glass Manufacturing
The raw material that is the largest component of glass is silica sand or silicon dioxide, SiO2. Glass is formed by melting the SiO2 and then cooling the melt before crystals can form. However, the melting temperature of the silica is about 1700 oC, and at that temperature the liquid phase is very viscous. Sodium oxide, Na2O, is added to the silica in the form of sodium carbonate in order to lower the melting temperature. In the heating, CO2 is driven off the leaving Na2O. The sodium carbonate serves as a flux in glass making. In order to stabilize the glass product, add strength to the product and make it resistant to water, calcium carbonate (CaCO3) is added. Again, in the heating, CO2 is driven off leaving CaO as the stabilizer in the glass. Broken glass, called cullet, may also be added to the mix. Other compounds may be added (see “Additives and Color”). There are many formulations for glass. This paragraph is based on the common soda-lime glass.
(October 2006 ChemMatters Teacher’s Guide, accompanying the article, “Glass: More than Meets the Eye”)
More on toughened glass
Thermally-toughened glass
Tempered glass (sometimes called toughened glass or heat-toughened glass) is used in applications requiring extra strength or thermal resistance, or where safety is a concern. It is 4–6 times as strong as regular glass and it does not shatter when it breaks, but instead completely crumbles into tiny pieces that don’t have sharp edges, unlike normal window glass that shatters into shards. In the diagram below, the piece of glass illustrated on the right side shows this tendency to fracture.
Tempered glass is made by heating annealed glass to very high temperatures (>600 oC) and then cooling it suddenly (quenching) with high-pressure jets of air. This process causes the molten outside surface of the glass to freeze into position, while the inside is still molten. As the molten inside cools, the molecules slow down and the entire center contracts, creating tension inside. It pulls the outside along with it and creating compression on the outside of the glass as it is pulled inward (see illustration below). The compression of the outside surfaces also tends to press closed any microscopic cracks or imperfections that could otherwise lead to system failure (breaking of the entire piece of glass). Tempered glass breaks when the toughened outer compressive layer is penetrated, exposing the inner area of tension.
Because tempered glass is under forces of compression and tension, any fabrication of the glass (e.g., cutting to size, drilling holes, etching or edging the piece) must be done prior to tempering. Any such work done on the piece after tempering makes it likely that it will fracture or at least will weaken the glass, thus negating the benefits of the tempering process.
Tempered glass is used in side and rear windows of automobiles (not windshields, though, due to the danger of the flying glass), tub and shower enclosures, microwave ovens, skylights, architectural glass doors, refrigerator shelves, cookware (think, Pyrex), etc. It is also used in smartphone screen savers.
Chemically-toughened glass

The quest for smartphone screens that won’t smash didn’t end with heat-tempered glass, because that glass still can—and does break. Enter Gorilla Glass. This is a chemically-tempered glass, as the Rohrig smartphone article states. A bath of a potassium salt, usually potassium nitrate (KNO3) is heated to 300 oC. The potassium ions in the bath replace sodium ions in the glass, near the surface. Potassium ions, larger than sodium ions (95 pm for potassium vs. 133 pm for sodium), wedge into the structure of the glass as they replace the sodium ions that migrated into the molten potassium nitrate, This causes compression of the surface of the glass and corresponding tension in the glass core, resulting in a very strong, shatter-resistant glass—chemically tempered.

This Web site provides a very short animation showing the heating of a piece of sodium glass, potassium ions moving into the glass, and then the cooling of the now-chemically-strengthened glass. (http://www.glastroesch-schienenfahrzeuge.ch/en/products/chemical-tempered-glass.html) Note: the text is not “polished”.
More on the history of heat-tempered glass—the “Prince Rupert’s drop”
The idea of heat-tempering via the balance of compression and tension inside glass is not a new development. The phenomenon was known as early as 1625. And in 1660 Prince Rupert of Bavaria gave some small glass drops to King Charles II of England for his examination (play), who in turn gave some to the Royal Society for scientific study. The tadpole-shaped drops had been prepared by heating glass until it was molten and then letting some molten drops of the glass fall into cold water, quenching them. They sizzled as they hit the water but, instead of shattering as you might expect, the drops remained intact. They were extremely strong, resisting pliers-squeezes and even hammer blows. Yet, a small scratch or break on the tail that trailed behind the drop would result in the explosion of the drop into myriad tiny pieces. The drops are known even to this day as Prince Rupert drops.
As the drop is dropped into the cold water, the outside is immediately cooled to freezing. The inside cools more slowly and gradually becomes solid. As it does so, the glass molecules inside pull together more closely and draw the solid outside molecules in toward the center, creating that balance between tension inside and compression outside. This effectively makes the drop heat-tempered, so it is very strong and shatter-resistant, as evidenced by the inability to break it with a hammer. But the thinner tail does not have the same compression as the thicker bulb, so it is not as strong. When the tail is broken, a crack is formed and a shock wave propagates through the tension zone swiftly through the entire drop. What we see is an explosion of glass.
This 6:38 video from “Smarter Every Day” shows several attempts (and lots of successes) at breaking a Prince Rupert drop. It uses ultra-high-speed photography (130,000 frames per second) to show the process of breaking, beginning at the tail end and propagating to the bulb. The narrator uses polarized filters to show the stresses inside the drops (caused by the tension and compression forces), and he also uses animation to help explain the compression and tension forces at work inside the drop. (https://www.youtube.com/watch?feature=player_embedded&v=xe-f4gokRBs) See the “In-class Activities” section below for a student activity you can do with your class.



  1. b) c)

  1. Example of a Prince Rupert’s drop: http://www.digitalreviews.net/digitalreviews/media/images/news/monthly/2013/04/2_prince_ruperts_drop.jpg

  2. Ready to squeeze the pliers at the tail: http://www.thisiscolossal.com/wp-content/uploads/2013/03/glass-1.gif (Note: clicking on this link provides a very brief video clip of the explosion)

  3. Pliers squeezed—explosion of Prince Rupert’s drop: http://www.wired.com/wp-content/uploads/blogs/geekdad/wp-content/uploads/2013/03/Prince_Ruperts_Drop.png

More on Gorilla Glass™
Corning, Incorporated has produced two videos, providing a brief history of glass that leads up to the development of the various editions of Gorilla Glass™:

  • “The Glass Age, Part 1: Flexible, Bendable Glass” (https://www.youtube.com/watch?feature=player_detailpage&v=12OSBJwogFc) and

  • “The Glass Age, Part 2: Strong, Durable Glass” (https://www.youtube.com/watch?feature=player_embedded&v=13B5K_lAabw).

These videos star Adam Savage and Jamie Hayneman from the television show MythBusters. In their inimitable style they explain the difference between regular soda-lime glass and Gorilla Glass. They discuss compressive strength and show a Prince Rupert drop as a prime example of how Gorilla Glass works.
Sapphire glass, more durable but also more expensive, may replace Gorilla Glass: (http://www.extremetech.com/computing/151146-your-next-smartphone-might-use-sapphire-glass-instead-of-gorilla-glass)
More on electronic displays
There are several different kinds of smartphone and other electronic device displays in use today, and many more are in research stages globally for potential future use, or in their infancy stages of actual production and use. Here’s a very brief run-down on each of them. The reference at the end of this section contains much more information of a scientific nature for each of the displays.
Displays being used today

  • Liquid Crystal Displays (LCDs):in many electronic display devices today and in the past

  • Active Matrix Organic Light Emitting Diodes (AMOLEDs): in Samsung products

  • Electrophoretic Ink (E-ink): black & white, in Amazon’s Kindle, image-persistent, low power requirements

Displays being researched for future use

  • Cascaded LCD: Invidia has stacked 2 LCDs on top of one another with a slight offset and used algorithms to sharpen the image to a 4K equivalent display

  • Quantum Dots (QDs) in televisions from The Creative Life (TCL, a Chinese company) and in the Kindle Fire HDX tablets: better color gamut and contrast

  • Liquid Crystal Additives: use carbon nanotubes to help stabilize LCDs

  • Transflective (TFT) LCDs: able to both transmit and reflect light, eliminating the need for backlighting, a big power drain

  • Vision Correcting Displays: use mathematical algorithms to correct users’ vision problems, like near- and far-sightedness

  • Crystal IGZO Transistors: Indium-gallium-zinc oxide semiconducting material: provides faster refresh rate and higher resolution

  • Nanopixels containing phase-changing material (PCM, made of germanium, antimony and tellurium (GST): highly power-efficient, persistent image, like E-ink

  • Interferometric Modulator (IMOD) now in Qualcomm products: uses thin-film technology (like butterfly wings) to change color, color-persistent, very low energy consumption

  • Flexible Organic Light Emitting Diodes (OLEDs): Samsung and LG are both using/researching these for curved television and smartphone displays; uses flexible polyimide film as the backbone of the display


More on the elements of smartphone chemistry
The infographic below, from compoundchem.com, describes some of the uses for some of the elements found in the typical smartphone. The creator of this site admits that the uses of many specific elements within the smartphone are very difficult, if not impossible, to find online. He cites the probability of trade secrets as the reason.



More on what smartphones can do FOR chemistry
While the rest of the background information above details what chemistry does for smartphones, smartphones are also doing great things for chemistry. Here are a few examples:
The abstract from the Bulletin of the Korean Chemical Society of the article

“Smartphone-based Chemistry Instrumentation: Digitization of Colorimetric Measurements”, authored by Byoung-Yong Chang, describes the use of a smartphone as a colorimeter.

This report presents a mobile instrumentation platform based on a smartphone using its built-in functions for colorimetric diagnosis. The color change as a result of detection is taken as a picture through a CCD camera built in the smartphone, and is evaluated in the form of the hue value to give the well-defined relationship between the color and the concentration. To prove the concept in the present work, proton concentration measurements were conducted on pH paper coupled with a smartphone for demonstration. This report is believed to show the possibility of adapting a smartphone to a mobile analytical transducer, and more applications for bioanalysis are expected to be developed using other built-in functions of the smartphone.
(Chang, B-Y. Smartphone-based Chemistry Instrumentation: Digitization of Colorimetric Measurements. Bulletin of the Korean Chemical Society 2012, 33 (12), pp 549-552)
Here is the reference to the actual article: http://journal.kcsnet.or.kr/main/j_search/j_download.htm?code=B120235
This article from the September 12, 2012 online issue of Science 2.0 provides the basic idea of how the smartphone colorimeter mentioned above works: http://www.science20.com/anirban_mudi/blog/mobile_chemistry_using_smartphone_make_colorimetric_measurements-93840.
Microscopes/magnifying lenses
Lenses that transform smartphone cameras into microscopes are available commercially. This one that magnifies 15x the digital zoom of the smartphone lens only costs $15 (as of 10/17/2012).


Scientists have also created an inexpensive lens made of polydimethylsiloxane, a clear polymer, that they then used with a smartphone as a dermatoscope, a (normally costly) magnifying device used by dermatologists to check a patient for skin cancer. (http://www.isciencetimes.com/articles/7162/20140505/scientific-breakthrough-transforms-smartphones-cancer-detecting-microscopes.htm)
This September 17, 2013 online article from Science Daily, “Smartphone 'microscope' can detect a single virus, nanoparticles” discusses the development at UCLA of a portable microscope that attaches to the smartphone camera. The device can detect a single virus and material less than 1/1000th the width of a human hair. The microscope “… can be used to perform sophisticated field testing to detect viruses and bacteria without the need for bulky and expensive microscopes and lab equipment. The device weighs less than half a pound.” (http://www.sciencedaily.com/releases/2013/09/130917093933.htm)
A device and app for detecting and diagnosing eye refractive problems for people in third-world countries has been developed by MIT scientists. The inexpensive ($2.00) device attaches to the smartphone; the user simply puts the device up to their eye and lasers inside detect problems and suggest what is required to effect the fix (i.e., what prescription is needed for glasses). (http://www.scientificamerican.com/article/8-apps-that-turn-citizens-into-scientists/?page=1)
This October 27, 2014 online article from iSPEX, “Citizen Science network produces accurate maps of atmospheric dust”, details an ongoing series of experiments in the Netherlands by scientists using data from non-scientists (average citizens). The experiment involved an inexpensive add-on device to, and an app for, smartphones (iPhones only) that provided (and continues to provide) data on atmospheric dust in the atmosphere. “Thousands of participants performed iSPEX measurements throughout the Netherlands on three cloud-free days in 2013. This large-scale citizen science experiment allowed the iSPEX team to verify the reliability of this new measurement method.” (http://ispex.nl/en/ispex-metingen-leveren-nauwkeurige-kaarten-van-fijnstof-boven-nederland-op/)
The article “Why Your Smartphone Needs an Infrared Sensor” in the January 22, 21015 digital edition of Popular Mechanics discusses the present-day uses of two new devices that connect to your smartphone to “see” objects’ infrared footprint (e.g., heat leaks around windows). Although author Dan Dubno doesn’t give any chemistry applications, it’s only a matter of time before they’re used in chem labs to determine temperatures of reaction vessels.


The smartphone’s sound recorder has been used by scientists to pursue research in oceanic biodiversity. (http://www.isciencetimes.com/articles/7162/20140505/scientific-breakthrough-transforms-smartphones-cancer-detecting-microscopes.htm)
This article from Science Reports on nature.com, “Rapid and reagentless detection of microbial contamination within meat utilizing a smartphone-based biosensor”, provides detailed information about a method that uses only a smartphone camera and a near-infrared (NIR) LED light source to preliminarily detect Escherichia coli in ground beef. Existing methods require antibodies, microbeads or other agents to detect the bacteria. (http://www.nature.com/srep/2014/140805/srep05953/full/srep05953.html)
The December 9, 2014 online edition of Phys.org provides this article: “New Cheap NFC Sensor Can Transmit Information on Hazardous Chemicals, Food Spoilage to Smartphone.” The article details the technology behind the MIT chemists’ application of chemiresistors, made from commercial near-field communication (NFC) tags already used in other fields, and adapted to detect gases associated with food spoilage and hazardous chemicals. The information they collect is communicated wirelessly to any smartphone held close to (within 5 cm of) the tag. (http://phys.org/news/2014-12-cheap-sensor-transmit-hazardous-chemicals.html) Here is a 1:36 video clip that describes briefly how the MIT chemists adapted the NFC tags for chemical-sensing: http://www.laboratoryequipment.com/news/2014/12/smartphone-sensors-see-hazardous-gases-food-spoilage.
This February 6, 2015 ScienceFriday.com article, Honey, I Shrunk the Lab: Testing for STDs on a Smartphone discusses briefly a new add-on device to smartphones that tests blood from a finger-prick for STDs: http://www.sciencefriday.com/segment/02/06/2015/honey-i-shrunk-the-lab-testing-for-stds-on-a-smartphone.html.
And for the chemistry behind swimming pools (hey, chemistry is everywhere, right?), there is this list of “Pool Apps for your Smartphone”: http://blog.poolcenter.com/article.aspx?articleid=6162.
Let’s not forget the usual ways the smartphone can help chemistry—by helping chemistry students. This article, “The Application of Smartphones and Two-dimensional Barcodes in a Chemistry Laboratory Manual”, discusses the teacher’s use of 2D bar codes to give students instant access to videos, blogs and laboratory data sheets via their smartphones. (http://www.sapub.org/global/showpaperpdf.aspx?doi=10.5923/j.jlce.20140201.01)
Even science supply companies are getting in on the act. Edmund Scientifics now has a “Smartphone Science Lab” ($19.95, as of 2/24/2015) for kids 8+. It provides 20 different science experiments you can do using your smartphone. (http://www.scientificsonline.com/product/smartphone-science-lab)
More on smartphones of the future (?)
As mentioned in Rohrig’s article, the smartphone is evolving so rapidly that it is difficult to predict what will come next. But here are two possible scenarios. The first describes how touch screens work and how graphene will play a large role in defining smartphones of the future; the second describes a more immediate evolution of the smartphone.
Until recently, most electronic devices were controlled by pushing buttons, typing on a keyboard, or using a mouse. Today, most cell phones and tablet PCs have touch screens that allow the user to make selections by touching icons or letters directly on the display screen.
The basic idea of how most of these devices work is simple. A layer that stores electrical charge is placed on the glass panel of the screen. When a user touches the screen with his or her finger, or with a stylus pen, some of the charge is transferred to the user, so the charge on the layer decreases. This decrease is measured by sensors located at each corner of the screen, and this information is relayed to a processor inside the device, which determines what kind of action to take.
All of this is possible because these devices use screens that have thin and transparent coatings that are conductive and can hold a charge. Most portable devices today have screens that are coated with a conductive layer made of indium tin oxide. But this material is brittle, so it is layered on glass to protect and support it. This leads to thick and inflexible displays.

Touch screens made with graphene as their conductive element could be printed on thin plastic instead of glass, so they would be light and flexible, which could make cell phones as thin as a piece of paper and foldable enough to slip into a pocket. Also, because of graphene’s incredible strength, these cell phones would be nearly unbreakable. Scientists expect that this type of touch screen will be the first graphene product to appear in the marketplace.

(Tinnesand, M. Graphene: The Next Wonder Material? ChemMatters 2012, 30 (3),
pp 6–9)
And here’s to the near future (almost present?) of the smartphone: Google’s Ara project (2012 –2015) comprises a modular smartphone, with inserts that can be added to or removed from a base unit to increase functionality of the smartphone. These slide-in, slide-out modules include, but are not limited to, better speaker, better camera, extra battery life, replaceable screen (if it gets broken), and even night vision. Other uses shown are: a digital thermometer (remember above?), AM/FM radio, Wi-Fi adaptor, heart-rate monitor, compass, and GPS system. It uses open software, so tech geeks and tech start-up companies can make their own modules. Google even provides the Modular Developers Kit that can be used to develop new modules. The phone is projected to be available in 2015, debuting first in Puerto Rico. See this video for a glimpse into the future (as of 4/1/2015): https://www.youtube.com/watch?feature=player_embedded&v=intua_p4kE0. So, any of the applications we discussed in paragraphs above could soon be in a smartphone module near you!

This illustration, taken in a screenshot of the video clip above, shows and describes some of the modules that will be available for the ARA smartphone when it debuts.

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