On the surface, the periodic table may seem nothing more than a giant list of names. A register where scientists can keep a record of all the elements and show them off to the world or a boring piece of art, used in science classrooms for decoration rather than for any practical use.
Such a simple view betrays the elegance and profound nature of the periodic table. Peer a little deeper and all kinds of patterns, connections and information can be found. Blocks and groups (columns) contain elements that have similar properties. These may be physical properties such as appearance, strength and whether they are solid, liquid or gas. It could be their chemistry: how reactive they are or the compounds they form. It could even been how the electrons are arranged in each atom. Despite these patterns, there are always exceptions, elements whose behaviour seems strange where compared with their neighbours.
In Part I of our periodic drama, we explored the first 56 elements, focussing on the unusual elements, those that are not commonly heard about or have weird, wacky properties. We carefully met the reactive elements and brushed passed the dull, inert ones.
Part II will see us complete our walk through the elements. Here, we will meet the super weights of the periodic table: the heaviest, the nastiest, the rarest and the synthetic elements. We may stop at element number 118, but that doesn’t mean the periodic table has to. What does the future hold? Can we continue making more and more elements? And how far can the periodic table go?
So, get yourself comfy, get the popcorn ready and have your periodic tables on hand (https://www.ptable.com/) as the concluding part of the periodic table begins.
Elements 57 – 71: The Lanthanoids
We begin with the first row of those elements usually found underneath the periodic table. These may seem to be out of place and it is tempting to think of this row as some sort of dumping ground for useless elements or useless scientists who do not know where they should go. The simple reason this row of elements is placed where they are is purely for visual reasons.
We have already mentioned how the periodic table can be split and viewed as different blocks based on how the electrons are arranged. By the time we reach element number 58, there are so many electrons that they hang out in a new place around the nucleus. This new place can only hold 14 electrons and so forms a new block that extends between elements 58 and 71. However, including these elements as a new block would make the periodic table very wide and so they are often placed underneath. But what are these elements? Collectively, they are known as the lanthanoids[1].
The lathanoids are so called due to their similarity to the element lanthanum. Technically, lanthanum is not a lathanoid, but is often included as one. This set of elements is also known as the rare earth metals, although this is a misnomer since some of them are rather common on Earth. Many of them can probably be found in your mobile phone!
Lanthanum (La), element number 57, is a metal soft enough to be cut with a knife – a kind of metallic butter. When combined with nickel, the alloy[2] LaNi5 is very good at absorbing hydrogen gas, making it an ideal material for storing hydrogen. You will also find lanthanum in the battery of hybrid cars (these are cars that contain a fuel powered engine and an electric motor). A battery typically contains two components, which in this case are made from different materials. At one end (known as the cathode) is a combination of nickel hydride and another metal. The other end (known as the anode) is made from an alloy of lanthanum.
When combined with oxygen, lanthanum oxides (LaO) are used in the glass lenses of cameras, where they help to improve how much light bends when it moves through the lens (technically this is called its refractive index and is an important factor for lenses).
One very cool application of lanthanum is a product called Phoslock. This gravel like substance is actually a type of clay used to clean and restore lakes, reservoirs and other types of standing water. When added to the water, the lanthanum forms strong attachments (binds) with any phosphates that may be present. Removing phosphates from the water prevents algae from growing and helps to get rid of that horribly, gloopy green/brown scum that forms in dirty water. The lanthanum phosphate forms a solid that simply lies at the bottom of the lake and the water returns to looking pure, clear and refreshing.
Right next to lanthanum lies element number 58, cerium (Ce) – the first proper lanthanoid in the series. You may find cerium oxide in your car exhaust where it is used as catalyst to help change nasty, harmful gases into more harmless ones. The idea of a self-cleaning oven is very appealing because, let’s be honest, no one likes having to scrub the oven. Well self-cleaning ovens do exist and the magical substance found inside them is cerium oxide. Here, it coats the walls of the oven and helps to reduce any spilt food into ash.
Cerium appears to have no use in the human body and luckily is not too toxic. Throughout history, cerium has been used in medicine. In the Victorian age, cerium nitrate – Ce(NO3)3 – was used to prevent sickness, whilst cerium oxalate was believed to help reduce coughing for those suffering from TB (tuberculosis). More recently, our Victorian friend CeNO3 has found use in treating burns. A weak solution of the chemical has been found to be an effective first treatment for those suffering from very severe and deep burns.
Cerium has not just saved lives through its medical ability. A Jewish chemist called Primo Levi, who wrote one of the first general science books on the periodic table, wrote about how cerium helped him survive the concentration camp Auschwitz during the Second World War. When metal cerium is struck it produces sparks, making it perfect for use in cigarette lighters. By making light flints from cerium, Levi was able to trade them for food, which no doubt helped his survival.
If you ever have used microphones or in-ear headphones then you will been very close to our next element. In fact, if you own a laptop or desktop computer then chances are your hard disk will also contain this element. This is because element number 60, neodymium, can be made into very powerful magnets when combined with iron and boron. These powerful NIB magnets – with the chemical formula NdFeB – are also found in the speakers and microphones of mobile phones. These magnets do however have a health warning. People who have been unfortunate (or stupid) enough to swallow these magnets have suffered major problems, especially when several magnets have been swallowed. The attraction between these magnets is so strong they will find each other inside the body, crushing and pinching the insides! Not very nice at all!
Neodymium, a hard, silvery looking metal, has also found uses in lasers. This includes Nd:YAG (which we met in Part I), a powerful laser that has been found uses in dentistry, medicine and for cutting steel. It is also widely find in research labs. Another neodymium laser, Nd:YVO4, can also be made to produce green light and is the main component in laser pointers. It is important to note that lasers can be dangerous especially to our eyes. Despite the use of neodymium for lasers, it is unlikely that we will be able to buy laser producing watches or glasses anytime soon – a setback for wannabe secret agents and superheroes.
All of the lanthanoids we have met so far are relatively common, even with their deceptive name of rare earth elements. Our next element, Europium (Eu), is however one of the rarer elements. In its pure form, europium is a shiny white metal that is very soft. One of its major uses is to provide red colour in the screens of TVs, computers and mobile phones.
We can also take advantage of the light emitted by Europium atoms (a feature called fluorescence). If you use, or have ever used, Euro bank notes then you will notice how colourful and detailed they are. Displaying not just how much they are worth, but an image of some grand building along with the EU flag in the corner. These bank notes are printed with a special (and secret) ink, which includes a fluorescent dye to which is attached europium. When the notes are put under a special laser, the paper itself appears black. However, where the dye and europium ink has been placed a magical light show appears. Green lights glow along the outline of the map of Europe, the stars of the EU flag shimmer red or yellow and hidden features emerge from the dull plastic note as sparkles of blue. This light display is certainly pretty and makes dull bank notes more exciting, but why go to so much trouble? Well, fake counterfeit notes will not show this dazzling arrangement of fluorescent, helping authorities to find, prevent and remove fake bank notes from being used.
Europium’s colourful display may be useful for spotting fake money, but its neighbour gadolinium (Gd) is useful for finding tumours in people. Gadolinium, element number 64, has found widespread use as an MRI contrast agent. MRI (Magnetic resonance imaging) is a common procedure used in hospitals to see what is happening inside your body. Unlike other possible treatments, MRI is painless (always a good thing!) and can be used on any part of the body.[3] So what role does the gadolinium play and what is a contrast agent?
We have already mentioned about the electrons in different elements are arranged differently. As they are being arranged, the electrons can either be on the own, or paired up with another one. Gadolinium contains five unpaired electrons making it respond to a magnet very easily (the correct term is paramagnetic). Before an MRI is done, patients may be injected with a solution containing gadolinium. This helps to enhance the image of our insides and makes the area containing any gadolinium really stand out. For example, in a grey image, areas containing gadolinium will appear as white. By making gadolinium compounds that find and attach to tumours, an MRI scan can clearly show areas of our body where cancer may be.
Without wishing to cause alarm, gadolinium on its own is highly toxic! However when surrounded and bound to large, cyclic structures – as it is in contrast agents – it loses this toxicity. Recent work though has raised concerns that gadolinium may remain in the brain after being used.
Elements 72 – 88
After the lanthanoids, the periodic table returns to its more familiar appearance. By this point we have reached period six of the periodic table. This includes the third row of the transition metals and includes the well-known elements platinum, gold, mercury and lead. It also includes some the densest and deadliest elements, as well as those that simple refuse to melt or boil!
The elemental trio of tungsten (W), rhenium (Re) and osmium (Os) can all boast some of the greatest physical properties on the periodic table. Tungsten has the highest melting point of all the elements[4], giving up its solid state at temperatures over 3400 °C. Coming in a distant second is rhenium, which melts at a slightly cooler 3180 °C. This rivalry still continues when it comes to which element has the highest boiling point. You would need to reach a scorching 5600 °C to boil both rhenium and tungsten.
Next to both of these elements, you will find osmium. Even though the melting and boiling point of osmium is very high, it wins the award for being the densest element (with a value of 22.59 g/cm3), narrowly beating iridium. This means that a teaspoon of osmium (around 112g) would feel as heavy as two medium sized eggs. However, unlike an egg and spoon race, the osmium would probably be easier to balance on the spoon!
The very high melting point of tungsten has made it the ideal element when very high temperatures are involved. Good old-fashioned light bulbs – the kind seen in cartoons when someone has a good idea – contain a small piece wire, called a filament, made of tungsten. These light bulbs work by passing an electric current through the wire that causes it to heat up and emit light. These filaments can heat up to several thousand degrees making tungsten, with its high melting point, an ideal material.
Tungsten can also be used to make very hard and strong materials. One such material is tungsten carbide, which you will find in dentist’s equipment as well as the ball in ball-point pens. The pen might well be mightier than the sword, but not without some help from tungsten.
Most people know that lead (Pb) and its compounds are toxic, such as tetraethyl lead, which was talked about in September’s molecule of the month. Lead is just one of harmful elements found in the toxic corner of the periodic table. Thallium (Tl) and Polonium (Po), elements number 81 and 84, are amongst the most poisonous and lethal substances on the periodic table. Throughout history, thallium has been the choice of poison for getting rid of your enemies – only one gram of this element is fatal! Thallium can also be absorbed through the skin, so even if you avoid swallowing it, any contact with your skin could also be deadly! But why is this element so toxic? The problem is that in our body’s thallium acts very similar to potassium, a vital element to our health. By pretending to be potassium, the thallium can sneak its way all around our body where it wreaks havoc. Symptoms of thallium poisoning include hair loss, fever, stomach pain and nausea. Your nerves would be affected as well, leading to numbness and a tingling sensation that would become more and more painful.
Polonium is so dangerous because of the intense radioactivity it possesses. Luckily, it is an extremely rare element so you are unlikely to come across it. However, it has been reported that as little as 1 microgram (a millionth of a gram) could be fatal. Strangely enough, polonium itself is not thought to be toxic. Polonium’s radioactivity means it has very few uses and normally would be a reclusive element, known only to chemists and periodic table fans. However, this element became infamous in 2006, when it was found to be responsible for the death of the Russian Alexander Litvinenko.
Our toxic and lethal corner of the periodic table contains one rather unusual element, bismuth (Bi), element number 83.
Despite being squashed between highly toxic thallium and hyper radioactive polonium, bismuth is harmless. In fact, bismuth has been used in medicines for many years now. The popular product Pepto-Bismol, used mainly in the US to relieve stomach issues is actually a bismuth compound known as bismuth subsalicylate[5] or pink bismuth.
Bismuth was believed to be the element with heaviest stable (non-radioactive) isotope. Research has shown though that it is actually slightly radioactive with a half-life of 20 billion billion years – a billion years longer than the age of the Universe. On a more day to day basis, bismuth oxychloride is used in make-up to give a shiny, pearl-like effect.
Unlike bismuth, many of the elements with no stable isotopes occur in very small amounts on Earth. As we pointed out the earlier, the reason we do not live in constant fear of polonium is because of how rare this element is and the short amount of time that any form of it exists for. Polonium begins a sequence of elements (astatine, radon, francium and radium) which are the rarest naturally occurring elements on Earth, mainly due to the radioactive and short lives. Astatine (At) is the rarest naturally occurring element[6]. It is so rare that no one has ever managed to get enough to see it with the naked eye. Although, funnily enough astatine is so radioactive that even if you were to find enough to see, it would produce enough heat to instantly boil itself away! The second rarest naturally occurring element is francium (Fr), element number 87. The most stable version of this element has a half-life of only 22 minutes and so doesn’t stick around for very long.
Elements 89 – 103: The Actinoids
As we reach the final period of the periodic table, we reach the end of the naturally found elements and enter into the synthetic world. Here, the elements have and will only ever be man-made. For some of them, only a dozen or so atoms have ever been made. The creation of these elements may seem rather crude and essentially involve smashing two nuclei together in the hope they stick together and form a new, larger and heavier nucleus – a new element. This is a bit like throwing two snowballs at each other. Sometimes the snowballs hit each other and either rebound or break apart. Other times, they stick together initially, but quickly fall apart and occasionally they stick together and stay together, forming a larger snowball. As simple as this seems, there is one important factor that makes this method difficult – the nuclei need to be moving fast, very fast, usually around 10% the speed of light, a rather rapid 30 000 000 meters per second. By comparison, Usain Bolt’s average speed was a little over 10 meters per second when setting the 100 m world record. None of these elements have any stable forms – they are all radioactive and decay over varying amounts of time. This continues the trend that started with bismuth and polonium.
We now come to the lower row of the elements sitting below the main periodic table, from actinium through to lawrencium. ADD. We saw earlier how the row above, the lanthanoids, was named because all the elements were similar to lanthanum. This is, however, not necessary the case with the actinoids, all of which are quite distinct from each other. The most famous elements of the actinoids are uranium and plutonium, which everyone instantly associates with nuclear weapons and power plants.
Actinium (Ac) glows a mystical pale blue in the dark. Thorium (Th) and uranium (U) are unusual in that, despite being radioactive, they decay very slowly with half-lives of millions and billions of years. This means that large amounts of these elements can still be found in the Earth’s crust.
Plutonium may be well known as an element of nuclear destruction and power, but it also marks the point at which the naturally occurring elements finish[7] and the man-made elements begin. By this point, the elements have very little use and are mainly the play things of scientists. There are a few exceptions though. Away from the nuclear world, the heat produced by plutonium’s radioactivity can be used as a heat or power source for space equipment and satellites, such as Cassini and Voyager.
The first of the synthetic, exclusively man-made elements is number 95, americium[8]. It is one of the few post-plutonium elements that have real world applications and are not confined merely to research labs. Americium was first made in 1944 by bombarding plutonium with neutrons. Although this element is radioactive and is therefore dangerous, one of its main applications is in helping to keep us safe.
Every student and working person will have experienced the loud, droning sound of the fire alarm. Some of us have even been unlucky enough to be woken up in the middle of the night and forced to line up in the cold and wet because the alarm has gone off. Nevertheless, fire alarms are essential for keeping us safe and warning us when there is fire and smoke. The vast majority of smoke alarms contain a small amount of americium. The radiation from the americium causes the air particles nearby to become charged and be attracted towards metal plates of the opposite charge (remember negative is attracted to positive and the other way around). This movement produces a current, which keeps the alarm quiet. However, smoke can interact with these charged air particles and disrupt the electric current, causing the alarm is ring out.
The only other actinoid element to have any use is californium (Cf), element number 98. As a radioactive element, californium is a source of neutrons, which can be used to make a device called a neutron moisture meter. This device can be used to measure how much water there is in soil or rock.
Towards the end of the actinoids, we reach the milestone of element number 100 – fermium. This element has no uses except in research labs, but is significant as being the last element that can be produced in large amounts. However, when we say “large” amounts, we are actually talking about micrograms, a millionth of a gram. This may sound a very small amount when compared with the everyday objects around us, but when it comes to the super heavy, synthetic elements it is a relatively big amount. If you still don’t believe that a microgram can be considered a big amount, then let’s explore the next element, Mendeleevium. This element, named after our famous periodic table formatter, can only be produced in femtogram amounts. A femtogram is a billion times smaller than a microgram, which suddenly sounds rather big! Even worse is the next element along, nobelium. Creating nobelium involves smashing together californium and carbon atoms, a process that produces only several thousand atoms! A very, very, very small amount indeed!
Elements 104 – 118 and beyond…
At long last, we have reached the final chapter in our periodic drama. These elements mark the end of the periodic table…for now. None of these elements are stable and exist only for minutes and hours. The very short lifetime of these elements makes them difficult to study and quite often their properties have to be predicted using computers or assumed to be similar to the elements above.
Because only very small amounts of each element can be created, proving you have successfully made a new element is a long and complicated process. It also leads to intense rivalry between different research groups, each claiming to have discovered the element first. As well as pride and fame, being the first to discover a new element also allows you to name it, usually after a famous scientist or location. Because of this, a furious argument over the first discovery and naming of elements 104 through to 106: rutherfordium, dubnium and seaborgium rumbled on for neatly forty years. The solution to this conflict also resulted in the naming of elements 107 to 109: bohrium, hassium and meitnerium.
To stress just how little of these elements are produced, let us look at element number 110, darmstadtium, named after the German city of Darmstadt where the research lab that first created the element is based. The experiment used to try and create darmstadtium involved hitting a lead target with atoms of nickel. Using this method, the research team were able to create a grand total of one atom of darmstadtium. Like any good scientists, they repeated the experiment and this time managed to create a more impressive nine atoms of the element. This was sufficient to claim the discovery, but really shows the extremely small amounts that are made of these new elements.
And so we reach the final scene of our periodic drama, the last two elements of the periodic table. Element 117, tennessine, is the most recently discovered, having been first created in 2010. Oganesson, element number 118, is the final element in the current periodic table and has the honour of being the element with the highest atomic number and atomic mass. As oganesson lies in group 8, this makes it a noble gas similar to the very inert argon and xenon, and lying just below radon. However, computer predictions suggest this element may be nothing like a noble gas, but it is unlikely a large enough sample will ever be made to really find out what properties oganesson possess.
So is this end of the periodic table? Is the story finished and the table complete?
Not yet. Research groups around the world have already been trying to create elements number 119 and above. You may be surprised to learn that even in the 1970s, attempts were being made to create elements in the 120s. As before, making these elements is not easy and only a small number of atoms may ever be created. It is, however, probably only a matter of time before new elements are discovered. This then raises the question of how far can the periodic table go? Could we reach element number 200, 500 or even 999, or is there a limit and if so where? There is some debate where the limit of the periodic table may be, but generally it is thought to be less than elements with an atomic number of 200.
Some say the limit is at 137, after which the electrons closest to the nucleus would have to travel faster than the speed of light – an impossible situation. More advanced calculations predict the limit to be at 173. Whatever the limit is, these elements are unlikely to ever be part of our everyday lives, the exception being that the periodic table found in every chemistry textbook and classroom will get a little bit bigger.
So there you have it, our periodic drama may have only covered a small portion of the elements, but those we have mentioned are less well-known. Those you may never have heard of, but are used somehow, somewhere in our everyday lives. Each element has a fascinating story to tell and it only gets more exciting and amazing when we start to combine the elements into molecules and compounds. As we celebrate 150 years of Mendeleev’s periodic table, it is far from the end for this spectacular arrangement and whilst an eventual limit may be reached, don’t be surprised if one day you see another row on your periodic table.
[1] You may sometimes see this group as elements written as lanthanides instead. The difference between lanthanides and lanthanoid is very small and often people taken both to mean the same thing. Strictly speaking, the elements from cerium (Ce) to lutetium (Lu) are known as the lanthanides. The lanthanoids are the same group of elements, but also include lanthanum (La) itself. BACK TO POST
[2] An alloy is a metal that also contains atoms of another metal or even non-metal elements. Steel, for example, is made from iron and carbon, whilst brass is a combination of copper and zinc. The advantage of alloys are they usually have much better properties (strength, reduced reactivity and so on) than the individual metal does. BACK TO POST
[3] Our body is full of water molecules (good old H2O) each of which comprises one oxygen and two hydrogen atoms. The nucleus of a hydrogen atom contains a single proton that acts as a very tiny magnet. This means that your body is full of tiny little proton magnets. When inside an MRI machine, a powerful magnet causes all the protons to line up and face the same direction. A radio wave is then passed through your body which causes some of these protons to spin and face different directions. Once this radio wave is turned off, the protons relax and line themselves up again so they are all facing the same direction. This creates a signal that can be viewed on a computer screen as a series of black, white and grey dots that are used to make an image of our insides. A contrast agent, such as gadolinium, affects how quickly the protons surrounding it relax. This shows up in the image and a much brighter region, allowing doctors to locate in the body where any gadolinium has collected, which may show the presence of any tumours. BACK TO POST
[4] There is some debate as to whether carbon’s melting point is higher. Even though carbon remains solid at temperatures higher than tungsten’s melting point, carbon does not actually melt. Instead it goes straight from a solid to a gas, a process called sublimation. So it is often argued that carbon does not have a melting point. BACK TO POST
[5] This molecule contains a component that is very similar to acetylsalicylic acid, otherwise known as aspirin. So it is therefore not surprising that bismuth subsalicylate is a useful medicine. BACK TO POST
[6] Any astatine present during the formation of the Earth has long since decayed. The main source of astatine is from the radioactive decays of the heavier elements such as thorium and uranium found in rocks and minerals. In fact, it has been estimate that at any one time, there only exists 1 gram of astatine on Earth BACK TO POST
[7] It is often claimed that uranium (U), element 92 is the last naturally occurring element and indeed you will see many textbooks refer to the 92 natural elements. However, the two elements after uranium, neptunium and plutonium, are naturally formed in tiny amounts from uranium and can therefore claim to be found naturally in nature. The vast majority of these two elements are however produced synthetically. BACK TO POST
[8] It is possible that this element occurred naturally millions years ago from reactions of uranium. However, with a half-life of much shorter than 10 000 years, then any americium that did exist, will have long decayed away. BACK TO POST
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