A couple months ago I introduced my element collection with an article about the display I built for it. Back then I had 88 elements, and now I have 92 which is probably the end of the line. So today, I’m sharing pictures and a little information about each element I have, and a few that I don’t have. It’ll take a while, so settle down with some snacks and enjoy the tour!
My sample of hydrogen is a tiny tube of tritium, a radioactive isotope that has a couple neutrons in its nucleus along with the proton. As it decays it causes a fluorescent substance painted on the inside of the tube to glow, and this constant glow should last for over a decade.
This sample is kind of boring, just a clear glass ampoule of invisible helium gas. I was hoping to set up small discharge lamps for the gases, but those require such high voltage it would be difficult to fit into the space I have to work with. Helium is the least reactive element and was first discovered in the sun by spectroscopy.
As the lightest metal by far, lithium has about half the density of water and easily floats in the mineral oil that protects it from oxidation. It’s the first of the alkali metals, and the least reactive. When placed in water, it fizzles around slowly without any of the exciting violence its relatives are known for.
If you ever encounter beryllium powder roaming free, run away. If there’s any chance you inhaled some, you should immediately see a doctor. Some people are more susceptible than others but anyone can be poisoned by this element, and when inhaled it can cause an incurable disease called berylliosis. Symptoms may show up anytime from weeks to decades after the exposure, and are similar to tuberculosis. All that aside, beryllium is an interesting element that is strong and lightweight, transparent to X-rays, and useful for many things. It’s also the main component in the mineral beryl, the deep green variety of which is called emerald.
Much like carbon, pure crystalline boron is extremely hard. As you might expect, so is boron carbide, which is the third hardest material known and used in tank armor, bulletproof vests, neutron radiation shielding, and as an abrasive. Boron carbide powder will quickly destroy a car’s engine if you pour it into the oil, so it has also been used for sabotage purposes.
Carbon is amazing in its versatility. Not only is it the basis of all life on earth, it also has numerous allotropes with wildly different properties, forms the hardest substances we know of, remains solid above the melting point of every other element (it sublimates rather than melting), and so much more. I chose to represent carbon with two samples: a piece of graphite and a small natural diamond.
You may not think about it much, but nitrogen is everywhere. Not only is 78% of our atmosphere comprised of nitrogen, it’s also the fourth most common element in your body and an ingredient in just about every drug. Like hydrogen, oxygen, fluorine, and chlorine, nitrogen gas is diatomic, meaning its atoms pair up rather than floating around solo like the noble gases, and the triple bond between them means that nitrogen compounds often release a lot of useful energy when broken apart. From DNA to fertilizer to explosives to Kevlar, nitrogen is one of the basic building blocks of our lives, as well as being involved in a lot of destruction. The same can be said about the next element, too.
Oxygen is the most common element in earth’s crust, because it’s the third most common element in the universe and is very reactive and readily binds to most elements to form less reactive compounds. Such a reaction is called oxidation, or if it’s very rapid, “burning”. This is why the atmosphere of the early earth didn’t have much oxygen, as any available oxygen gas would have combined with other elements to form gaseous compounds like carbon dioxide, liquids like water, and solids like quartz.
Fluorine is one of the most difficult obtainable elements to collect in pure form, due to its extreme reactivity as the lightest of the halogens. My sample is actually 33% fluorine and 67% helium in a quartz ampoule; the addition of helium helps suppress reactions between the fluorine and quartz. It’s so reactive that it can form compounds with most of the noble gases as well as every other element. Due to its eagerness to react, fluorine can form some very stable and inert substances. Teflon, for example, is simply made of carbon and fluorine, and because the carbon-fluorine bond is so strong there are only a few extremely reactive chemicals (like the alkali metals) that are able to affect it.
Neon is the second least reactive element, after helium. Both of them can form unstable compounds in certain conditions, such as high pressure or very low temperatures, but in normal conditions they are complete loners. For a long time it was thought that they wouldn’t react at all, but neon compounds were finally discovered in the 21st century.
Eleven of the elements have symbols that don’t match the modern names, most because they originally had Latin (or New Latin) names. Sodium used to be called natrium, from nitron/natron, the name for sodium bicarbonate (aka baking soda) that originated in ancient Egypt. Sodium is much more reactive than lithium, and cheaper than potassium, so it’s the ideal alkali metal for dropping in water. It doesn’t always explode, but a large enough chunk (at least a gram) has a really good chance of going off with a bang every bit as loud as a large firecracker. The explosion is not caused by the ignition of hydrogen gas as originally thought, but rather is initiated by a coulomb explosion which shoots spikes of the molten metal in every direction, greatly increasing the surface area where the standard reaction can take place.
Magnesium is the lightest metal that is stable enough to use in the construction of everyday objects. It’s about 74% heavier than water, and more than 30% lighter than aluminium. The only lighter metals are lithium, sodium, potassium, rubidium, and calcium, all of which are much softer and more reactive. One of the coolest properties of magnesium is how bright and hot it burns, which is less cool when the burning magnesium is a Porsche engine block. I once drove by an old 911 burning in the left turn lane of an intersection, and when I passed by again hours later, it was still smoldering. Magnesium fires are very difficult to extinguish, but fortunately the bulk metal is also difficult to ignite. Shavings and powder, on the other hand, must be handled with care.
When aluminum was first isolated in usable quantities, the process was so difficult that it was more expensive than gold, despite it being the most common metal in earth’s crust. I made this little ingot of aluminum by melting down soda cans and kitchen foil with my propane torch, and then I made about 30 more before I got tired of the tedious process. I still have a good stash of scrap aluminum, which I plan to melt down when I have access to a better source of heat, and use for casting chess pieces and other items.
Because silicates (silicon oxides plus other elements) make up around 90% of the earth’s crust, silicon comes just after oxygen in the Earth’s Crust Popularity Contest, and just ahead of aluminum. Quartz is a form of silicon dioxide, also called silica, which is the main component of sand and glass. The closely related feldspar minerals are more common than quartz, comprising around 60% of the earth’s crust on their own, and they’re made of silicon, oxygen, and aluminium, plus potassium, sodium, and/or calcium.
My favorite thing about the sample of phosphorus in my collection is that it’s the amorphous red allotrope, which happens to be almost exactly the same color as my bed sheets. This is one of the chemicals used in matches, either in the striking strip on the box or in the match head. The white allotrope of phosphorus is much more reactive and will ignite on its own in air, so it’s a little too extreme for matches.
I’m very fond of my sample of sulfur, which is a beautiful crystal about 20 mm long from Italy. One of only three yellow elements (if you count gold and exclude the slightly gold-ish tint of cesium and a few rare earths), sulfur burns with a blue flame and turns dark red when molten, both of which I observed on accident when I tried to seal some in a small ampoule and got it too hot. Like oxygen, it is fairly reactive and forms compounds with most other elements, many of which are known for smelling bad. The odors of garlic, rotten eggs, skunk spray, and many other notoriously stinky things are due to sulfur compounds.
I originally had a tiny ampoule of liquid chlorine under pressure, but it was slowly leaking so I replaced it with a boring ampoule of invisible gas. Pure chlorine is much easier to deal with than fluorine, but still a nightmare gas that reacts with almost anything. One of the most insane chemicals ever is chlorine trifluoride, a terrifying substance that even the Nazis decided was too dangerous to use. A spill of about 900 kilograms once burned through a foot of concrete and then three feet of gravel, because all you can do with such an incident is wait for it to finish burning. John Drury Clark, a chemist who developed rocket fuels, wrote this about chlorine trifluoride: “It is, of course, extremely toxic, but that’s the least of the problem. It is hypergolic with every known fuel, and so rapidly hypergolic that no ignition delay has ever been measured. It is also hypergolic with such things as cloth, wood, and test engineers, not to mention asbestos, sand, and water — with which it reacts explosively. It can be kept in some of the ordinary structural metals — steel, copper, aluminum, etc. — because of the formation of a thin film of insoluble metal fluoride which protects the bulk of the metal, just as the invisible coat of oxide on aluminum keeps it from burning up in the atmosphere. If, however, this coat is melted or scrubbed off, and has no chance to reform, the operator is confronted with the problem of coping with a metal-fluorine fire. For dealing with this situation, I have always recommended a good pair of running shoes.”
Add one more proton and electron to chlorine, and it turns from a very reactive and dangerous gas to a completely benign noble gas. Argon comes after nitrogen and oxygen as the third most abundant gas in the atmosphere, at a concentration of nearly 1%.
The symbol for potassium is K, from its New Latin name, kalium. It’s more reactive than sodium and burns with a pretty purple flame. When alloyed with sodium, the result is a metal that’s liquid at normal temperatures and at least as reactive as pure potassium.
A fundamental component of bones, teeth, and shells, calcium is the most common metallic element in many animals. It’s also a major rock-forming element, and one rare isotope was instrumental in creating several superheavy elements, being slammed atom by atom into a kindaheavy element until they fused to make something with 20 more protons. We’ll come back to that at the end of the tour.
It’s unfortunate that scandium is so expensive, because it’s a very useful metal. With aluminum it makes lightweight alloys as strong as titanium and as hard as ceramic, which is perfect for the aerospace industry, baseball bats, bicycle frames, and many other applications. Because of scandium’s high cost, however, titanium alloys are more commonly used.
The remarkable thing about titanium is that it has the highest strength/weight ratio of any elemental metal. There are stronger metals, and lighter ones, but titanium is the best of both worlds, and it also resists corrosion nearly as well as platinum. In pure form it’s already as strong as some steel, but its mythical reputation for strength is a little overblown. Titanium rings can be cut off just fine in an emergency, nobody’s going to remove your finger instead. What this element really excels at is forming very strong and lightweight alloys that resist corrosion, which are used in an enormous number of different industries, especially aerospace. Its oxides are used for pigments, and almost all white paint now is made with titanium, a much better choice than lead. My personal favorite application of this metal is my titanium spork, which I consider to be the most perfect utensil ever created.
Vanadium is another strong and relatively lightweight metal, but it’s much rarer than titanium and around 33% heavier. Its main use is in steel alloys for added strength.
Like vanadium, chromium is a major component of certain steels, both to add strength and to increase resistance to corrosion. Stainless steel contains at least 10.5% chromium, and the metal stamps I used to mark my homemade ingots are chrome-vanadium steel, a common alloy for tools because of its high strength. Because of its resistance to corrosion and lasting shine, chromium is often plated over base metals for protection and decoration, especially on cars and plumbing fixtures.
The brittle manganese is an important element for all life we know of, and similar to iron. It rusts in the same way, and is usually obtained from iron ores. Non-biological uses for manganese include pigments and batteries. If you’ve ever taken apart a zinc-carbon or alkaline battery, the black powdery substance is manganese dioxide. Its most common use is in steel, to remove oxygen, sulfur, and phosphorus, as well as to increase corrosion resistance. It’s also alloyed with aluminum to make beverage cans.
In Latin, iron was called ferrum, thus the symbol Fe. It is the base metal of magnets and steel, the most common element in our planet (thanks to the molten iron core), and the last element produced by fusion in large stars. It’s the buildup of iron that ultimately triggers a supernova, which then produces the more extreme conditions required to create the rest of the elements. My sample is a fragment of the Campo del Cielo meteorite, which struck an area that is now in Argentina several thousand years ago. Some 100 metric tons of the meteorite have been found so far, with the largest fragment weighing 37 tons. Its composition is over 92% iron and almost 7% nickel, with a little bit of cobalt and other trace elements. Meteorites like this came from the cores of failed planets that broke up during the tumultuous birth of our solar system.
Another important metal for alloys, cobalt is famous for its distinctive blue compounds that have been used as pigments for thousands of years. It was the first new metal discovered since the seven of ancient times, when it was purified in 1735.
One of the world’s major sites for nickel production is the Sudbury Basin in Canada, the site of a meteor impact nearly two billion years ago. Likely because of their access to large quantities of the metal, Canada is one of the few countries that has made coins of pure nickel. My sample is a 5-cent coin from 1965, which is probably just as extraterrestrial as my iron meteorite fragment.
Copper’s Latin name was cuprum, and it was the first metal humans learned to use some 9,000 years ago. Like its fellow group 11 elements silver and gold (the trio is sometimes referred to as “noble metals”), copper is an excellent electrical conductor and can be found in its native form as natural nuggets, like the one from Michigan that I obtained for my collection.
I made my own zinc ingot by melting down a few pennies, which is only illegal if it’s done for fraudulent reasons like selling the metals for profit…exceptions are made for purposes such as art, education, jewelry, novelty, etc, which is why pressed penny souvenir machines are perfectly legal. Up to 1982, American pennies were mostly copper, but when it became too expensive they switched to a zinc core with a thin copper plating. These days, pennies once again are worth less than their component metals, so I think it’s time to get rid of them entirely instead of criminalizing people who take advantage of that fact to melt and sell them for scrap metal prices. Who needs one-cent coins anymore?
The fun thing about gallium is that its melting point is about 86° F, so you can melt it in your hand. And unlike the other metallic elements with very low melting points (rubidium, cesium, and mercury), it won’t burst into flames or burn your skin off or poison you. It’s relatively non-toxic, though it does stain things, corrodes and weakens some other metals, and wets glass. For my sample I put about four grams in a glass ball and shook it, to turn it into a spherical mirror. I also alloyed some of my extra gallium with a bit of indium, tin, and bismuth to make metal that is liquid even after being refrigerated for several hours.
With germanium we depart the transition metals for a bit, and enter the strange diagonal section of the table occupied by “metalloids”, elements with intermediate or mixed traits between those of metals and nonmetals. Typically these are boron, silicon, germanium, arsenic, selenium, antimony, and tellurium, though several other elements may be included depending on the criteria. The distinction is a bit arbitrary, but metalloids are generally more brittle and less conductive than metals, and behave chemically like nonmetals. Germanium is quite rare and has some important uses in electronics, like fiber optics, infrared, LEDs, and solar cells. It was the original semiconductor used in transistors and other devices, but mostly replaced in that role by silicon.
While arsenic is famously poisonous, it is also a necessary trace element for many animals. Its main use is in lead alloys for added strength, and it also has applications for electronics.
All animals require trace amounts of selenium, which like sulfur is implicated in some bad smells. Outside of biology its main uses are for pigments, and in the production of glass to remove green or yellow tint from iron impurities.
Possibly the most unique element in terms of appearance, bromine is also one of the most frightening. Bromine, being another halogen, is much like fluorine and chlorine except it’s a liquid at room temperature. A dark, angry-looking reddish-brown liquid that releases clouds of deadly fumes into the air whenever it isn’t contained. The vapor is an immediate threat to your life at just 3 ppm. If it gets on your skin it will quickly cause a nasty chemical burn. Drop aluminum into bromine and it will burst into flames. As you might expect, my sample is very small and sealed in a glass ampoule. I also keep a sodium thiosulfate solution on hand for capturing the bromine in case of a spill.
Because it has several emission lines across the spectrum, krypton is useful in gas discharge lamps as a source of white light.
Like the previous alkali metals (lithium, sodium, and potassium), rubidium follows the trend of getting more reactive. It can spontaneously burn in air, and reacts instantly and violently with water. For safety and to save money, my sample is a few milligrams in a tiny glass ampoule.
Strontium is very similar to calcium and is similarly deposited in bones, which is why the radioactive isotope strontium-90 is one of the most dangerous components of nuclear fallout. However, the stable isotopes pose little danger to your health. Because the ratios of strontium isotopes vary from place to place, the region of origin for old human bones and teeth can be determined by analyzing their strontium content. This also helps us trace migration patterns of ancient humans and animals. In technological use, strontium’s main application is in the front glass of a CRT monitor to absorb X-ray radiation. As CRTs are replaced by newer technology, demand and production of strontium are changing significantly.
Yttrium is chemically very similar to the lanthanides (“rare earth” elements), which we’ll come back to later. It’s always found associated with them in ores such as ytterbite, a mineral discovered near and named after the town of Ytterby in Sweden. It has a few uses in electronics and medicine, as well as a trace component in various alloys to give them specific properties like better ductility or more strength at high temperatures.
With a high melting point and strong resistance to corrosion, zirconium is similar to titanium and used in alloys for similar purposes. Its dioxide and the mineral zircon also have applications where resistance to high temperatures is needed, such as refractory materials and metal casting molds, as well as in ceramics, jewelry, and abrasives.
Niobium’s major use is in steel alloys, where a small fraction of a percent can increase hardness and high temperature stability. It is also an important element for various superconducting alloys.
While it may seem like a more obscure element, molybdenum is essential for all eukaryotes and some bacteria. Its extreme melting point and high strength also make it a useful additive for many alloys.
Technetium is the lightest element with no stable isotopes, one of only two that come before lead. Because the longest-lived isotope has a relatively short half-life of 4.2 million years, the only technetium that exists in the earth’s crust now is a small amount created via the decay of other radioactive elements. I did not expect to get a sample of it, but then it popped up on eBay in the form of a compound I’m pretty sure is tetraphenylarsonium pertechnetate, (C6H5OH)4TcAsO4.
This is the first of the platinum group metals, and the most common. It’s slightly more common than gold, making it the eighth least common stable element in earth’s crust. It’s also the densest of the first 71 elements. Like the other platinum metals, it mainly has uses in electronics and as a catalyst.
Not many years ago, rhodium cost over $10,000 an ounce. Its price has dropped since then, but it remains one of the rarest and most expensive metals. To save money, my sample is a tiny piece of ribbon. It’s often used as a wear and corrosion resistant coating, especially on jewelry.
The majority of palladium is used in catalytic converters, along with platinum, as they are the most effective catalysts for converting dangerous exhaust gases to the less troublesome nitrogen, carbon dioxide, and water vapor. This means that both of these precious elements can actually be mined from the dust along heavily traveled roads, and also why jerks often screw up the exhaust of junkyard cars by cutting out the catalytic converters. Other uses for palladium are numerous, such as fuel cells, electronics, medicine, dentistry, and of course jewelry.
Ag is an abbreviation of argentum, the Latin word for silver. My sample is a beautiful crystalline nugget from a mine on the California/Nevada border. Silver has the highest electrical conductivity of any metal, and an enormous number of applications beyond its traditional use as currency. It’s one of the seven metals identified and used by humans in prehistoric times, the others being copper, gold, tin, mercury, iron, and lead.
Cadmium is dangerously toxic, much like lead, and its major uses in pigments, rechargeable batteries, and corrosion resistant coatings are declining as less toxic alternatives take its place. It shares similarities with both zinc and mercury, which occupy the spots above and below it in the periodic table.
One of my favorite elements, indium is an extremely soft and stable metal that can be safely handled in elemental form and even chewed; its hardness is comparable to taffy. Indium has important uses in electronics, notably on smartphone screens in the form of indium tin oxide (ITO), a conductive substance that is transparent in thin layers. It’s also used in semiconductors, solders, and soft metal vacuum seals.
Tin’s symbol is Sn because its original name was stannum. When pure it is quite soft, though a little tougher than indium, and has a low melting point which makes it a popular choice for casting small objects like chess pieces and toy soldiers. It can be hardened significantly with the addition of about 1% copper to make a version of pewter. Adding a little tin to copper also has a hardening effect and we call the result bronze, which was the first metal alloy humans learned to make.
Stibium was the Latin name for antimony, and the source of its symbol Sb. It looks and feels very metallic, but is typically classified as a metalloid. Its compounds were used in ancient times for medicine and cosmetics, and in modern times its most important use is in flame retardant materials. Like arsenic, it is commonly alloyed with lead to increase its hardness.
Tellurium is a very rare element in the earth’s crust, surpassed in rarity only by the platinum metals, rhenium, and gold (ignoring radioactive elements). It’s also one of the elements you do not want to touch. Not because it’ll hurt you, but if any gets into your body it will make you reek of garlic for weeks, even in tiny amounts. Its main applications are alloys, solar panels, and semiconductors.
After bromine, the halogens turn solid with iodine, which is still almost as difficult to contain because it sublimates easily into a purplish gas. It is the heaviest element essential for human life, being found in thyroid hormones. It has an enormous number of important uses in sanitation, medicine, pigments, photography, catalysts, purification of other elements, and more.
Xenon was the first noble gas for which a compound was synthesized; xenon hexafluoroplatinate was discovered by Neil Bartlett in 1962 and proved the noble gases could in fact form compounds.
Because of the extreme reactivity of cesium, preparing and storing the pure metal is so expensive that it costs significantly more than gold. It is also one of five metals with melting points within the normal range of temperatures on earth, along with mercury, gallium, and its fellow alkali metals rubidium and francium. Cesium melts a few degrees lower than gallium, so you can melt it in an ampoule with just the heat of your hand.
One of the most interesting uses for barium is imaging the digestive system. Since it is opaque to X-rays, patients are given a barium sulfate “meal” to make their intestines visible in X-ray images. The pure metal has only a few minor uses, while the white sulfate is useful for various purposes in paint, ink, plastic, and rubber, as well as in drilling fluid for oil wells.
The rare earth elements aren’t called that because they’re rare…lanthanum for example is almost three times more common than lead in the earth’s crust, and cerium is abundant as copper. The “rarity” comes from the fact that all of these elements are very similar, and don’t occur in concentrated ores, so obtaining the pure metals is a difficult and expensive process.
One of the major uses of cerium is in ferrocerium “flints” for lighters, which also contain iron and several other rare earth elements. Scrape steel or another hard edge against it, and you get a shower of sparks. Cerium dioxide is also used as an abrasive for polishing glass.
Because the lanthanides have such similar properties, there are few uses for individual ones that couldn’t be done by others. Praseodymium has a few unique uses, but mostly it tags along with others like neodymium and yttrium.
Most people will recognize this element thanks to its use in the most powerful type of permanent magnet, an alloy of neodymium, iron, and boron. Because of that, this element is the most commonly encountered lanthanide in everyday life, found in electric motors, speakers, hard drives, and pretty much anywhere that a strong permanent magnet is needed.
Like technetium, promethium has no stable isotopes and is extremely rare, as the longest-lived isotope has a half life of only 17.7 years. It was used in place of radium in luminous paint for a short time in the 20th century, before safer alternatives became standard. The isotope used for paint has a half life under three years, so this old watch I found on eBay may not actually have any promethium remaining in it. At least it did at one point.
Samarium alloyed with cobalt makes the second-strongest type of permanent magnet, which is preferred over neodymium magnets in some cases due to retaining its magnetic properties at much higher temperatures.
The most reactive of the lanthanides, europium is very difficult to preserve without oxide discoloration. It turns dark rapidly when exposed to air, and a small piece like mine would oxidize away into a pile of greenish powder in just a few weeks. In order to keep it shiny, it has to be sealed in a glass ampoule with argon or another inert gas. Europium can be used to make incredibly bright phosphorescent paints and dyes.
Along with iron, nickel, and cobalt, gadolinium is one of only four elements that are ferromagnetic at normal temperatures, though it loses that trait above 68 F. A few other elements can become ferromagnetic at very low temperatures.
Like europium, terbium’s main use is in phosphorescent substances, though it also has a few applications in electronics.
Below -188 C, dysprosium is ferromagnetic with one of the highest magnetic strengths of any element. Above that temperature but below -94 C, it turns antiferromagnetic, and above that it becomes paramagnetic (weakly attracted to magnets but unable to become one itself). However, it has very few unique uses.
Holmium has the highest magnetic permeability of any element, so it’s sometimes used to strengthen magnetic fields. There’s not much else to say about it.
Erbium’s main use is in lasers, thanks to emission wavelengths and other properties of its ions that make it perfect for certain optical fiber and laser surgery applications.
As the rarest of the stable rare earths, thulium is one of the most expensive and obtained by extracting trace amounts from rare earth minerals. One of its main uses is in lasers, for the same reason as holmium.
Yttrium, Terbium, Erbium, and Ytterbium were all named after the Swedish town of Ytterby, where they were originally found. This element holds the record for the most accurate atomic clock ever made, which is stable within two parts in a quintillion.
The last of the lanthanides, lutetium is also the hardest, most dense, and has the highest melting point. It has few uses, though its radioactive isotopes have shown promise in experimental medical applications.
Because of its great similarity to zirconium and comparable rarity, hafnium doesn’t have many uses, and zirconium can substitute for most of them. It’s found in small concentrations in zirconium minerals and is difficult to separate, which makes it costly to use. Its limited applications are mostly in alloys and compounds for electronics and aerospace.
Tantalum occurs in association with niobium, and has very similar properties. Its main use is for smaller, more efficient capacitors in portable electronics. Also, like hafnium, it is useful in special alloys for demanding applications. It’s quite inert and has a very high melting point, so it has been used for light bulb filaments. However, element 74 is both cheaper and makes better filaments.
Rather than Latin, tungsten’s symbol comes from the original German name, wolfram, which is still its name in several European languages. It’s another of my favorite elements due to its extreme hardness, and the density being nearly identical to that of gold. It has the highest melting point of any element, and the highest tensile strength of any pure metal. A single tungsten carbide cutting tip for my Dremel helped me slice through a lot of steel, whittle down the heads of welded bolts on my truck’s exhaust, and more. It is the primary material used for light bulb filaments, and surprisingly is the heaviest element that is essential for some living organisms, as it’s used by a few species of bacteria and archaea. It also forms the densest gas known, the dangerously corrosive tungsten hexafluoride, which is about eleven times heavier than air. The sample I chose for display is one of the more expensive in my collection, a solid one-inch cube of pure tungsten. My 1.25-inch cube of magnesium weighs two ounces; the smaller tungsten cube weighs more than ten ounces. The density difference is so great it’s like comparing a marble to a ping-pong ball.
Rhenium, osmium, iridium, and platinum are the only stable elements denser than gold. The main use for rhenium is in nickel-based alloys for turbines in jet engines and other demanding applications, to increase strength at high temperatures. It has the second highest melting point, after tungsten, and the highest boiling point of any element.
Osmium has a beautiful bluish tint, and its claim to fame is being the densest known element. Some transuranic elements may be denser if it were possible to assemble their atoms into solid form, but osmium reigns among touchable elements with almost double the density of lead, at 22.59 g/cc. Since iridium is so close (22.56), it took some work to figure out which one was actually denser. Osmium was briefly used for light bulb filaments, but tungsten is cheaper and more stable.
If you want rarity without radioactivity, iridium is your element. It’s the rarest stable element in earth’s crust, with about 1 atom for every 100 billion atoms of silicon, a thousand times rarer than gold. The second-rarest, osmium, is almost ten times more common. Both iridium and osmium are used in various alloys where extreme durability is needed, such as fountain pen tips and electrical contacts. For a time they were also used in record player needles, but turned out to be less durable than sapphire and diamond. Iridium can be found in some high-performance spark plugs, and because it is the most corrosion resistant metal it’s also used for special crucibles, electrodes, and other applications where most metals would be destroyed.
One of the interesting things about the heavy platinum metals and gold is that they came from space. Due to their high density, these elements sank with iron to the center of the molten earth when it formed, and what we dig up now came from later bombardment of the planet by asteroids. Platinum itself is valued similarly to gold, sometimes more and sometimes less depending on supply and demand. It has many uses across numerous industries, especially as a catalyst.
Gold is an impressive element even aside from its mythical reputation and high value. It’s incredibly malleable, able to be hammered or drawn into extremely thin sheets and wires. It’s almost entirely impervious to corrosion and an excellent electrical conductor (only surpassed by silver and copper), which is why it’s used on sensitive electrical connections in computers where oxidation would be a big problem. I collected a 4 mm bead by recovering gold foil from about 75 old sticks of RAM and a few other computer parts. It isn’t a very cost-effective way to obtain gold due to all the acid required and hazardous waste produced, but I wanted the experience of collecting gold myself. When I was young I always dreamed of finding a gold nugget, but never did and making my own was the next best thing. The four other nuggets in my sample are natural ones from Alaska.
My collection of metals that are liquid below room temperature has three samples: sodium-potassium alloy (NaK, usually pronounced like “knack”), gallium-indium-tin alloy (aka “galinstan”), and elemental mercury. It’s a shame that mercury is so toxic, because it’s a beautiful and fascinating element, and the only one that remains liquid at 0° F (bromine freezes under 19° F). The original New Latin name, hydrargyrum, literally means “water silver”. Its high density and low viscosity make it great fun to experiment with, as it flows like water but has more than 13 times the density. The only stable elements that will sink in mercury are numbers 73-79. Lead will float in it like wood in water.
You might worry about lead and mercury poisoning, but the element between them takes deadliness to a new level. Thallium and its compounds are highly soluble in water, and easily absorb through skin. Along with arsenic and polonium, thallium is one of the few elements potent enough to be an effective poison for assassination, and the odorless, tasteless sulfide was widely used for rat poison until a few accidental human poisonings prompted the US to ban it in 1972. My one-gram chunk is safely encased in polyester casting resin.
The original Latin name for lead, plumbum, is where we get the symbol Pb as well as the English word plumbing and its relatives. Despite its reputation for being heavy, lead is actually less dense than all of the platinum group metals and only slightly more dense than silver. However, due to its relatively high density, corrosion resistance, low melting point, softness, and abundance, it has been widely used for thousands of years in applications where that combination of traits is useful. Because it is so toxic, many uses have been replaced with safer alternatives, but lead remains a highly important element thanks to its unique nature. The abundance of lead relative to other heavy elements is due to it being the endpoint of three major decay chains of radioactive elements.
Along with tin, bismuth is one of the best elements to play with. Both of them are safe to handle, both have low enough melting points to be liquefied on a kitchen stove, and both are beautiful with interesting properties. Bismuth expands when it cools and forms spectacular stair-stepping square crystals, which you can easily make yourself by removing them from the pool of melted bismuth before it solidifies fully. The oxides also turn different colors depending on what temperature the metal was when they formed, and they’re slightly iridescent, so the color of the crystals is a sparkling metallic rainbow. While it’s sometimes called the last stable element, bismuth is technically radioactive, but the half life is so incredibly long that for our purposes it’s practically stable.
This is one of the elements I didn’t expect to obtain. The problem with polonium is that it’s very radioactive and an extremely potent poison which has been used in multiple assassinations. A speck the size of a grain of sand is plenty to kill you; a gram could kill ten million people. So I don’t have the longest-lived isotope, or a significant amount, but it’s possible to buy a check source with a tiny bit of polonium-210. The half life is only 138 days, so if my math is correct the amount I have should be completely gone after about twelve years.
Here we have the first element of which I cannot obtain a sample. Astatine has a half life measured in hours, and a visible specimen would violently vaporize and kill anyone nearby. To fill the spot in my display, I used my woodburning tool to inscribe the element symbol, number, atomic weight, and density into a piece of nice maple wood.
The main problem with collecting radon is that its half-life is just a few days, so any sample will be gone very quickly. Since it’s produced by the decay of radium, some element collections use a radium-containing ore to represent it. I decided to use a few antique watch hands to produce a small but real presence of radon as the radium in the paint decays.
Francium has an even shorter half life than astatine, just 22 minutes for the longest-lived isotope, so it barely exists in nature and has never been seen directly. The largest amount we have ever collected in one place was only 300,000 atoms.
During the first half of the 20th century, radium was used to make luminescent paint. Since the longest-lived isotope has a half-life of about 1600 years, some antique watch hands with radium paint may still have a faint glow, but the fluorescent material also breaks down over time so most will not. Radium is particularly dangerous because it shares chemical traits with the other alkaline earth metals, including calcium, and when ingested ends up in your bones where it poisons you with radiation from inside for the rest of your suddenly shortened life. For luminescent paint now we mainly use tritium, which is much less dangerous.
Actinium is the last element that I haven’t obtained which might be possible to get. The longest-lived isotope has a half life of almost 22 years, so in nature it only exists in extremely small amounts along with uranium. Any available samples of the pure element would likely have to be synthesized by blasting radium with neutrons in a nuclear reactor.
With a half life of more than 14 billion years, thorium-232 is by far the most stable of any purely radioactive element. A handful of stable elements have longer-lived radioactive isotopes, but at this point we’re talking about a half life greater than the age of the universe (the longest half life known, for tellurium-128, is more than 160 trillion times longer). Thorium is therefore much less radioactive than even uranium and has several uses, including in tungsten welding rods and gas lantern mantles, although its decay products are more dangerous and its use is declining. I have a gram of thorium dioxide because the pure metal is nearly impossible to find and very expensive.
Another element I didn’t expect to find is protactinium. It has a long enough half life for collecting, but like most rare radioactive elements it only exists naturally on earth as a relatively brief stop in the decay chain of uranium, and is therefore present in tiny amounts in uranium ores and very expensive to refine. It’s also produced in nuclear reactors from thorium, which is likely where mine came from. My sample is a piece of aluminum with a very thin layer of protactinium plating.
Uranium is the last element that collectors can obtain in macroscopic samples, and also has a much longer half life than most of the intensely radioactive elements leading up to it. My sample is about a gram of depleted uranium, which has most of the bomb-making 235 isotope removed. What’s left is mainly uranium-238 with a half life of 4.5 billion years. Since it is nearly as dense as gold, hard as titanium, and only weakly radioactive, depleted uranium is used for armor-piercing ammunition by the US military, which is a bad idea because it’s still very toxic and contaminates the land with uranium dust wherever it’s used in action.
An actual sample of pure neptunium is unobtainable, but fortunately it is what americium-241 decays into. So I can represent both neptunium and americium with these parts from old smoke detectors. After about 400 years, half of the tiny sample will be neptunium.
The infamous 94th element is completely illegal for ordinary people, and all of America’s plutonium is stored and closely guarded in one location. The only exception is for a handful of older people who have plutonium-powered pacemakers, because you can’t really confiscate those until the owner dies. However, I found a loophole that allows me to have a very tiny but still real presence of the element in my collection. The little green chunk you see above is a glassy substance called trinitite, which was formed from melted sand in the Trinity bomb test way back in 1945. Since it was a plutonium bomb, trace amounts of plutonium are present in trinitite, along with many other radioactive isotopes. Since it has been decades since the test, the highly radioactive isotopes have long since decayed and trinitite is perfectly safe to handle. Collecting anything from the test site is now illegal, but pieces that were collected a long time ago are still available on the market for collectors. I was lucky enough to find an affordable little chunk on eBay.
Smoke detectors use a tiny amount of americium dioxide as a radiation source, which allows for highly sensitive and accurate detection of smoke particles. This is the last element that is legally obtainable in any form (unless you’re working in a scientific lab with the proper permits), and the sample of the element itself isn’t visible since it’s around 1/100,000th the weight of a grain of rice and contained inside a small piece of metal. Americium-241 has a half life of 432.2 years.
Elements 96 and up mostly have very short half lives and no uses outside of research. They are created by bombarding a heavy element target with extremely fast-moving atoms of a lighter one until they happen to fuse. For example, element 118 was produced by slamming calcium (20) into californium (98). That’s the last element we’ve found so far. Element 118, oganesson, is named after Yuri Oganessian, a Russian nuclear physicist who’s 84 now and still working on superheavy elements. Despite falling in the noble gases group, oganesson may actually be a solid. However, its physical properties are a matter of calculation and conjecture since we’ve only produced three or four atoms total since it was first discovered in 2002, and they don’t last very long.
No further elements have yet been synthesized because of several technical challenges, but scientists continue to try, hoping to find what’s called an “island of stability”. The idea, as predicted by some models, is that somewhere after 120 there might be elements that are stable enough to be useful outside of research. A new device is currently being constructed at Mr. Oganessian’s lab in Russia to hopefully create elements 119, 120, and beyond. While it’s unlikely I’ll ever be able to add more to my collection, I eagerly await the discovery of more elements and the things we will learn from them.