Kamis 28 Juli 2017, Fakultas Matematika dan Ilmu Pengetahuan Alam dan ke-12 fakultas beserta program studi Universitas Jember secara serentak melaksanakan yudisium bagi calon wisudawan dan wisudawati. Berbagai persiapan dilaukan bagi para mahasiswa aktif dan para wisudawan untuk menyambutnya, mulai dari pernak-pernik yang akan digunakan selama yudisium sampai dengan mental karena kebahagiaannya. Pada periode ini, fakultas matematika dan ilmu Pengetahuan Alam Universtias Jember meluluskan 44 wisudawan dan wisudawati, dengan konfigurasi 16 Kimia, 7 Biologi S2 Biologi 2 orang, 16 Fisika, dan S1 Matematika 3 orang dan S2 Matematika 3 orang. Pada yudisium kali ini, mahasiswa berpredikat “Cumlaude/Dengan Pujian” jatuh pada Dana Iswara Putra dengan perolehan IPK 3,67 dan lulus kuliah selama 3 tahun 7 bulan 16 hari. Dana yang sering teman-teman panggil, memberikan sambutannya di depan para wisudawan dan wisudawati pada acara yudisium tersebut. Apresiasi diberikan kepada Dana Iswara Putra beserta kelima belas wisudawan dan wisudawati kimia lainnya yang telah berhasil melewati masa perkuliahannya. Harapan dan doa disematkaan kepada seluruh wisudawan dan wisudawati, semoga ilmu yang diperoleh selama berkuliah di Fakultas MIPA jurusan Kimia ini bisa bermanfaat untuk diri sendiri dan untuk masyarakat luas karena Indonesia membutuhkan orang-orang yang berani memunculkan inovasi-inovasinya untuk kemajuan bersama.
Spektrofotometri visible disebut juga spektrofotometri sinar tampak. Yang dimaksud sinar tampak adalah sinar yang dapat dilihat oleh mata manusia. Cahaya yang dapat dilihat oleh mata manusia adalah cahaya dengan panjang gelombang 400-800 nm dan memiliki energi sebesar 299–149 kJ/mol.
Elektron pada keadaan normal atau berada pada kulit atom dengan energi terendah disebut keadaan dasar (ground-state). Energi yang dimiliki sinar tampak mampu membuat elektron tereksitasi dari keadaan dasar menuju kulit atom yang memiliki energi lebih tinggi atau menuju keadaan tereksitasi.
Cahaya yang diserap oleh suatu zat berbeda dengan cahaya yang ditangkap oleh mata manusia. Cahaya yang tampak atau cahaya yang dilihat dalam kehidupan sehari-hari disebut warna komplementer. Misalnya suatu zat akan berwarna orange bila menyerap warna biru dari spektrum sinar tampak dan suatu zat akan berwarna hitam bila menyerap semua warna yang terdapat pada spektrum sinar tampak. Untuk lebih jelasnya perhatikan tabel berikut. Continue reading
Biocompatible, jelly-like materials that can repair themselves without losing their colour could find uses in photonics or biomedicine
Scientists in China have created hydrogels that show self-repairing properties combined with lasting structural colours. This new class of material could be used for tissue engineering or to build photonic integrated circuits and biosensors.
Many organisms – including birds, butterflies and beetles – display structural colours. These arise when light rays are scattered by tiny structures and then interfere with one another at certain wavelengths. This natural phenomenon has inspired researchers to create materials with similar optical properties. Hydrogels with structural colour have been made, but everyday use can damage these materials. If they could heal themselves that would be a solution, but it is challenging to retain their colours after healing.
A team led by Yuanjin Zhao at Southeast University, Nanjing, now has an answer to this problem. The researchers fabricated a composite material consisting of a stable scaffold – prepared using a methacrylated gelatin hydrogel and silica nanoparticle templates – filled with a glutaraldehyde cross-linked bovine serum albumin hydrogel containing the enzymes glucose oxidase and catalase. The structural colour of the hydrogels is provided and maintained by the scaffold, which is composed of inverse opal photonic crystals – 3D periodic structures with photonic band gaps that locate and reflect light with certain wavelengths. The self-healing properties are supplied by the protein filler, which uses the reversible imine attachment of the glutaraldehyde cross-linker to lysine residues of the protein as a repair tool. The enzymes keep the self-healing process going by adjusting the pH of the system in the presence of glucose.
Zhao explains that the micro- and nanostructure of the hydrogels could be preserved in this way. Although the reflection properties were slightly affected at the joining points, the original colour was maintained throughout the rest of the material on both sides. ‘This could not be achieved in pure self-healing hydrogel systems because their neighbouring nanostructures tend to fuse together, causing the destruction of the periodic photonic scaffolds and the related structural colours,’ Zhao says. By using different sizes of silica nanoparticles for the templates, the researchers could produce hydrogels of different colours. The self-repairing properties of the materials also allowed them to create complex structures such as 3D integrated photonic paths or a yin and yang motif.
David Weitz, a physicist who studies soft condensed matter at Harvard University, US, says that the use of structural colours ‘makes the materials more robust and better able to use the light’. ‘In addition, they can renew themselves, automatically recovering from damage, providing a new means of assembly and making them much more robust for practical applications.’ Weitz points out that each component plays an important role: ‘The materials are very cleverly fabricated by combining properties of different ingredients,’ he says. The scaffold guarantees the structural stability of the hydrogels while the protein filler provides the self-repairing properties.
Zhao says that the new hydrogels could serve as building blocks for many applications. ‘Our method can be used to construct different kinds of composite materials with self-healing properties including materials for novel photonic circuits, tissue engineering biomaterials or biosensor materials.’
Y Zhao et al, Proc. Natl. Acad. Sci. USA, 2017, DOI: 10.1073/pnas.1703616114
Pola makan adalah salah satu cara untuk mencegah kanker usus besar. Berikut makanan yang memiliki peran penting dalam menurunkan risiko kanker usus besar.
Kanker usus besar adalah salah satu penyebab utama pada pria dan wanita setelah kanker paru-paru, demikian menurut American Cancer Society pada 2013.
Bahaya, metode pencegahan dan pilihan pengobatan untuk kanker usus besar, tidak banyak diketahui secara luas, karena lokasi dari usus besar itu sendiri. Mengingat usus besar terhubung ke anus, sehingga orang mungkin enggan atau malu membicarakannya.
Dibandingkan dengan pap smear atau deteksi dini kanker serviks dan deteksi dini kanker payudara, masih banyak orang yang belum tahu bahwa kanker usus besar atau kolon juga bisa dideteksi dini.
Perlu diketahui juga bahwa setiap orang yang memiliki orang tua, saudara, atau saudara yang menderita kanker usus besar, memiliki risiko mengalami hal yang sama sebanyak dua hingga tiga kali lebih besar dibanding orang yang tidak punya riwayat keluarga dengan kanker usus besar.
Deteksi dini kanker usus besar telah menyelamatkan banyak nyawa dan sangat penting bagi mereka yang berusia 50 tahun ke atas. Pasalnya, 90 persen kasus terjadi pada kelompok usia itu. Meski kini juga semakin banyak usia muda yang menderita kanker usus besar.
Deteksi dini memiliki tingkat akurasi atau presisi yang cukup dan dapat mendeteksi polip prakanker sebelum berubah menjadi kanker sepenuhnya. Kanker usus besar sangat dapat disembuhkan jika berhasil ditemukan ketika masih stadium dini.
Pola makan adalah salah satu cara untuk mencegah kanker usus besar. Karena kanker ini berkembang dari sel abnormal pada lapisan usus besar atau rektum, maka gizi memainkan peran yang cukup besar dalam meningkatkan atau menurunkan risikonya. Berikut ini makanan yang dianjurkan untuk mencegah kanker usus besar:
Serat sangat faktor yang sangat penting untuk memerlancar pencernaan dan mencegah munculnya polip.
Alpukat adalah salah satu jenis makanan tinggi serat, begitu juga gandum utuh, oatmeal beras merah, dan kacang-kacangan hitam.
Makanan kaya antioksidan adalah pilihan yang baik untuk menangkal semua jenis sel kanker karena dapat menetralisir efek negatif yang disebabkan oleh radikal bebas.
Makanan seperti bayam, kale, brokoli, ubi dan wortel merupakan sumber antioksidan alami.
Rempah-rempah seperti jahe dapat bertindak sebagai anti-inflamasi yang berguna untuk membunuh sel-sel kanker usus besar.
Rempah-rempah lain yang memiliki fungsi yang sama yaitu bawang putih, kunyit, oregano, dan bawang merah.
Probiotik mampu merangsang usus dan merupakan sumber bakteri baik yang berguna untuk menjaga flora usus Anda tetap sehat dan seimbang.
Selain yoghurt, makanan lain yang kaya akan probiotik antara lain adalah acar, sup miso, dan cuka sari apel atau apple cider vinergar.
(Bestari Kumala Dewi/Kompas.com)
Ahli kimia dari China mengusulkan sebuah ide baru yaitu menggunakan kekuatan rumput laut untuk meningkatkan kemampuan baterai masa depan.
Selama ini, fokus penelitian terhadap penyimpanan energi hanya berfokus pada senyawa yang berbasis karbon, seperti grafena.
Namun, seorang ahli kimia dari Universitas Qingdao, China, Yang Dongjiang, mengusulkan sebuah ide baru yaitu menggunakan kekuatan rumput laut untuk meningkatkan kemampuan baterai masa depan.
Menurut Yang, struktur alga laut dapat dikombinasikan dengan logam untuk menghasilkan material baterai yang lebih baik, dan dapat diproduksi terus menerus.
“Kami ingin memproduksi material berbasis karbon melalui jalur ‘hijau’ yang sebenarnya. Karena rumput laut dapat diperbaharui, kami memilih ekstraknya sebagai prekursor dan contoh untuk mensintesis karbon berpori hirarkis,” ujarnya.
Yang bekerja dengan sebuah tim yang ditarik dari Qingdao, dari pekerjaan lamanya di Universitas Griffith, Australia, dan Laboratorium Nasional Los Alamos di New Mexico.
Mereka memproduksi nanofiber kobalt-alginat dengan struktur yang tahan lama serupa kotak telur. Fiber tersebut dapat digunakan untuk mendorong kinerja baterai dan kapasitor, perangkat elektrik yang dapat menyimpan dan melepaskan tenaga dalam banyak perangkat elektrik.
Walaupun telah dipublikasikan di jurnal ACN pada tahun 2015, penemuan Yang dan timnya dipresentasikan dalam pertemuan Perhimpunan Kimiawi America di San Francisco pada minggu lalu.
Sebenarnya, ini bukan kali pertama para peneliti menggunakan rumput laut untuk membuat baterai yang lebih baik. Namun, Yang bersama timnya berkata bahwa mereka telah mampu menambah jumlah tenaga yang tersimpan dalam masing-masing gram baterai lithium-ionnya secara signifikan dengan menggunakan bahan yang mereka produksi.
Yang dan timnya mengklaim, jika diproduksi dengan kualitas yang cukup tinggi, baterai ini berpotensi mampu melipatgandakan rentang waktu penggunaan mobil listrik.
Akan tetapi, penemuan ini masih jauh untuk dipasarkan. Yang berkata bahwa lebih dari 20.000 ton rumput laut perlu dipanen setiap tahunnya untuk memproduksi bahan yang diperlukan dalam skala industri.
(Lutfy Mairizal Putra/Kompas.com)
Harnessing nitrogenase enzyme makes key fertiliser material while generating electricity
Ammonia-producing proteins from humble nitrogen-fixing soil bacteria could help flip humanity’s fertiliser consumption from a massive energy drain into a power generator, thanks to a biofuel cell that reacts atmospheric nitrogen with hydrogen.
Today’s dominant and energy-intensive Haber-Bosch process also uses nitrogen and hydrogen to make ammonia. But its conditions, at around 500˚C and 200 times atmospheric pressure, mean it contributes up to 3% of global carbon dioxide emissions. ‘We could do it at room temperature and ambient pressure while simultaneously producing small quantities of electrical energy,’ says Shelley Minteer from the University of Utah, US, whose team developed the fuel cell.
Most biological fuel cells focus on increasing electricity generation from oxygen and hydrogen or glucose. By contrast, Minteer’s team realised that they could use the nitrogenase enzyme to replace the oxygen with nitrogen. Nitrogenase hasn’t been exploited before partly because it degrades in oxygen.
Having isolated the enzyme and kept it away from air, the researchers also faced the problem that electrons usually move slowly between enzymes and fuel cell electrodes. They therefore used methyl viologen to shuttle electrons in both compartments of their cell. In one compartment they put nitrogenase, nitrogen and a carbon paper electrode. The other, separated from the first by a membrane that allows only protons through, contained hydrogen, the enzyme hydrogenase that converts hydrogen to protons, and another electrode. The cell produced around five milligrams of ammonia for each milligram of nitrogenase, and passed 60 milliCoulombs of electrical charge between compartments.
Ammonia and power output can be continuous if the cell is kept supplied with its chemical fuels, which are hydrogen and the biological ‘energy’ molecule ATP. Eliminating ATP is an important hurdle to overcome, Minteer admits, which the group is working on.
They envision getting hydrogen from the same source as the current Haber-Bosch process, energy-intensive steam-reforming of methane. Minteer highlights that the energy their cell generates during the final step would reduce emissions during ammonia production. But she adds that her coauthors from CSIC, in Madrid, Spain, recently produced hydrogen using a photosynthesis protein and light. That could potentially erase ammonia’s carbon footprint altogether.
Producing the cell shows the team’s ‘deep understanding of the enzyme behaviour’, comments Katherine Holt from University College London. ‘The next question will be to improve enzyme stability and longevity for long-term use and to develop large surface area electrodes to allow for scale up.’
R D Milton et al, Angew. Chem. Int. Ed., 2017, DOI: 10.1002/anie.201612500
A twist on redox flow battery chemistry affords record performance
By simply adding bromide ions into a zinc–iodide battery, scientists from Hong Kong have reported the highest energy density for aqueous flow batteries to date.
Redox flow batteries have received growing attention as a cost-effective energy storage solution. Very different to traditional batteries, flow batteries make use of two different electrolyte solutions. When demand requires it, the solutions are pumped into a reactor, flow past each other and exchange electrons across a membrane. This provides a flexible approach to the energy storage conundrum. As flow battery expert James McKone from the University of Pittsburgh, US, explains: ‘The idea is to store large quantities of energy in liquid-phase electrolytes that can be held in very large, low-cost tanks for hours or even days at a time.’ However, the energy densities of flow batteries lag behind more developed technologies like lithium-ion batteries.
Researching a zinc–iodide flow battery, Yi-Chun Lu’s group from the Chinese University of Hong Kong have come up with an ingenious yet simple solution to exploit its full potential. ‘We pushed the limits of this system, and realised that we are actually wasting one third of the iodide ions as a complexing agent!’ comments Lu. ‘We asked ourselves, how can we fully utilise this battery chemistry?’
Zinc–iodide batteries contain a small amount of free I2 molecules, which are stabilised by iodine ions present in the system to form an I3– complex. Lu’s team introduced bromide ions to stabilise these I2 molecules – freeing up that third of the iodide ions to function as an active redox material. The increase in concentration of the active species gave an instant 20% improvement in capacity relative to a control system, with an energy density of 101Wh/l – the highest ever achieved experimentally for aqueous flow batteries.
Excitingly, the approach could work on other systems. ‘Not only does this concept apply to aqueous flow batteries, but also to non-aqueous types – it’s really looking at how to stabilise this active redox couple, and this concept applies in both types of battery,’ says Lu. ‘It would be interesting to see if analogous approaches would be even more broadly useful in other candidate flow battery electrolytes,’ McKone adds.
This article is free to access until 20 April 2017
G-M Weng et al, Energy Environ. Sci., 2017, DOI: 10.1039/c6ee03554j
The shocking start to the electrical age
In March 2017, Elon Musk, chairman of Tesla, flamboyantly proposed a solution to South Australia’s chronic power shortages in the ever-worsening summer heat. He would meet peak electricity demand by building a wall of batteries capable of storing up to 100 MWh of electricity; and it would be operational in 100 days or he would give it away for free. The news was just the latest indication of how spectacularly the economics of electricity storage have shifted in recent years. Yet the problem of storage takes us right back to the earliest days of electrical discovery, when a semi-accidental discovery by a gentleman scientist set the world on the road toward an electrical future.
Ewald von Kleist was born with a silver spoon in his mouth. The von Kleists were one of the more prominent noble families in the Prussian aristocracy, which for generations would supply high ranking administrators and military officers for the state – almost all of them called Ewald. Little is known of his childhood, but he went to university in Leiden, Netherlands in the 1720s where he studied law and theology. But while he would later become dean of the cathedral chapter in Kamień Pomorski, Poland, he also seems to have fallen under the spell of Willem ’s Gravesande, who introduced Isaac Newton’s work to the Netherlands and quantified the idea of kinetic energy, and Jean-Nicolas-Sebastien Allamand, his Swiss–Dutch pupil. When von Kleist returned home to Pomerania he took up science as a hobby, a common pastime for educated gentlemen of the day.
The 18th century was the age of weird electrical phenomena. Building on the century-old observation that objects could be charged simply rubbing one against another, all kinds of electrical ‘machines’ had been built. Wonderful demonstrations were devised. Among the most famous was Stephen Gray’s ‘The Flying Boy’, in which a small child was suspended by silk threads and then charged up, giving off spectacularly amusing sparks to anyone who approached. Among the masters of the public demonstration was Georg Matthias Bose (no connexion with Satyendra Nath Bose who developed the quantum mechanics of even spin particles in the 20th century), whose demonstrations were particularly flamboyant and piquant – in the ‘Electric Venus’ an attractive young woman was made to stand on a disc of insulating resin and charged up. Men in the audience were then invited to come up and kiss her, only to receive a nasty shock on the lips. Then, with the lights in the room extinguished, Bose would charge up a volunteer or assistant dressed in a suit of medieval armour equipped with sharp spikes. As the voltage rose, a blue-violet corona discharge could be seen in the darkness, a ghostly effect effect that Bose called ‘beatification’.
But among the japes there was real science. Bose showed that electrical conductors could become charged provided they were insulated from the ground using suitable material. He ‘electrified’ water in a drinking glass, and drew sparks from it using a finger or, more theatrically, with a sword. It presented a contradiction: fire could somehow pass through water. In public, Bose heightened the drama by setting fire to alcohol using a spark.
His demonstration experiments caused a sensation. Von Kleist, who had an electrical machine of his own, probably wondered whether the electricity could not be stored in the liquid itself. On 15 October 1745 he filled a small medicine bottle with alcohol or water and stoppered it, having hammered a nail through the cork to allow the electricity to reach the liquid. He then touched the nail to his machine. In the dim evening light he noticed a ‘pencil of fire’ around the nail, which lasted while he walked 60 paces around the room holding the bottle. When he touched it with his finger he received a massive electrical shock that stunned his arm and shoulder – enough to make von Kleist extremely wary of his bottle.
Astonished by his discovery, he wrote to several academics in Berlin, Hallé, Leipzig and Gdánsk, all of whom failed to reproduce the effect. He may also have written to university friends in Leiden, because four months later the university’s professor of physics Pieter van Musschenbroek reported an almost identical experiment in letters to the French scientist René de Réaumur. Arguments have swirled among historians about how the Leiden experiment came about. It is known that a lawyer Andreas Cunaeus, who spent his spare time with van Musschenbroek and Allamand, was involved and he is generally agreed to have received the first major jolt in Leiden.
Were the three aware of von Kleist’s work? Van Musschenbroek has been dismissed by historians as an indifferent electrical experimenter, tending to spend more time repeating others’ work carefully than on embarking on anything new. We may never know the precise sequence, but the uncertainty over priority has led to the gradual disappearance of the term Kleistian, to be replaced by the more generic Leyden (Leiden) jar – a term coined by French scientist Jean-Antoine Nollet, who translated van Musschenbroek’s work.
Von Kleist died less than three years after his discovery, probably oblivious to its significance. The ability to store charge opened up new possibilities in the study of electrical phenomena. Metallic coatings on the inside and outside of the jar improved its performance, but American scientist Benjamin Franklin in particular showed that the charge was stored on the glass rather than the metal. He also began to link them in series (‘in cascade’) to make a battery of Leyden jars. In Bologna, Luigi Galvani used the jars to make dead frogs twitch and likened electric eels to biological Leyden jars; Alessandro Volta (Chemistry World, June 2011, p58) used them to demolish Galvani’s speculations.Kleist has also been referred to, rather improbably, as ‘the father of the telegraph’ due to the role Leyden jars played in its development.
Perhaps there is some irony that, while today there has never been a greater need to store electricity, the first scientific studies of electricity were made possible by a reliable storage device. There really is nothing new under the sun.
Compact system turns waste plastic into fuels, allowing boats to power themselves while cleaning up the ocean
A retired research chemist has developed a small, portable reactor that uses a catalysed pyrolysis reaction to take discarded plastic and produce gasoline and diesel fuel directly. The idea is that supply ships could have this technology on board, enabling plastic waste collected to be converted into fuel that goes straight into their own tanks.
The technology, developed by Swaminathan Ramesh, formally of BASF, is a metallocene catalyst deposited on a porous support material that, when combined with a controlled pyrolysis reaction, produces high yields of fuel from polyethylenes, polypropolyenes and polystyrenes that needs no further refinement. ‘You don’t have to separate them out, they all can go into the same hopper,’ said Ramesh, who presented his work at the American Chemical Society’s Spring 2017 meeting in San Francisco. ‘The reaction is very efficient – we get a 90% to 95% yield.’
Ramesh explained that the reactor itself is continuously being fed plastic, which is heated as it goes through so that it is the right temperature when it hits the reactor, and the end product is immediately removed. ‘You can just operate it 24 hours a day and it takes up a [small] space,’ Ramesh said. ‘Ten pounds [of plastic] will give you a gallon of fuel depending on how pure the plastic is.’
To create this plastic-to-fuel conversion system, Ramesh partnered with long-time sailboat captain James Holm, the founder and executive director of Clean Oceans International, a California-based non-profit working to address marine plastic pollution.
‘Commercial shipping doesn’t have a method of recycling their plastic, this would be ideal for them,’ Holm stated. He also suggested that remote resort communities would greatly benefit from such technology because they could avoid having to ship out plastic waste to be recycled elsewhere. ‘Forty years at sea I have seen a steady decline in the health of the ocean, most notably the plastics problem,’ Holm recalled. ‘We wanted the option if we found and collected plastic in large enough quantities … to do something practical with it – just burying it in a landfill didn’t seem like the right response.’ Billions of pounds of plastic waste are currently estimated to be littering the world’s oceans.
When Holm looked into the existing plastic-to-fuel conversion technologies, he found that these systems were too large to work for his purposes of traveling by boat to remote areas. ‘We wanted something that was small enough to travel with us, hopefully even on board a vessel,’ Holm said.
The hope is that Ramesh’s plastic-to-fuel conversion system will be in operation on vessels in a few years. Ramesh and Holm will kick off a demonstration project for the city government of Santa Cruz, California to see whether the technology can help the city address unrecyclable plastic waste and create diesel fuel to power vehicles.
The next step involves scaling up. Ramesh already has the design plans to build the next-generation of his machine that can produce 2,000lbs of fuel per day, and even another one that can make 10,000lbs daily. ‘It costs around $1.5 million, but you will get back your money in 15 or 18 months, even at today’s low gasoline and diesel prices,’ he says.
Lanthanum and actinium, or lutetium and lawrencium? Time to pick a side
Like many chemistry undergraduates of my generation, I accepted Albert Cotton and Geoffrey Wilkinson’s Advanced inorganic chemistry as gospel. So when Cotton and Wilkinson presented the periodic table with lanthanum and actinium in group 3 of the d block, underneath scandium and yttrium, then that’s how it was. Their lanthanide and actinide series – the f block – floated freely beneath, running from cerium to lutetium and from thorium to lawrencium, and slotting into the ‘short form’ table, well, somehow or another, in a manner that didn’t greatly preoccupy me.
But do a Google search for images of the periodic table and this isn’t what you’ll see. A few retain Cotton and Wilkinson’s format – such as the CRC handbook of chemistry and physics. But many leave the sixth and seventh rows of group 3 undefined, labeled only ‘La–Lu’ and ‘Ac–Lr’. Others assign those two positions instead to Lu and Lr, with La and Ac now in the f block. A few, such as the Royal Society of Chemistry’s, keep La and Ac in the group 3 column while identifying only Sc and Y as truly belonging to the group.
What to make of it all? One option is to conclude that there is no definitive periodic table. Every chemist knows the arguments about where hydrogen should sit, given that it is by no stretch of the imagination comfortable atop the alkali metals. But that debate is mild compared with the fury that has been incited in arguments over group 3.1–4 Should we agree to disagree?
This doesn’t seem terribly satisfactory. The periodic table is widely considered chemistry’s prize exhibit: the most elegant condensation of all chemical lore, its ‘beautiful idea’ fit to stand alongside natural selection, the DNA double helix and the Dirac equation. How embarrassing, then, to admit that it doesn’t actually have a definitive shape at all.
Besides, the table is said to be dictated by physics. It’s not some arbitrary or empirical concoction: it has a structure defined and explained by the quantum theory of the atom, which governs the electronic configurations of elements. Out of that fundamental theory emerges not only Wolfgang Pauli’s Aufbau principle for the filling of electron orbitals but also the so-called Madelung rule for determining the ordering of the periodicity. This stipulates that the ordering of orbital filling follows the sequence of increasing quantum numbers n+l, where n is the shell number and l the orbital angular momentum: l=0,1,2,3… corresponds to the s, p, d, f orbitals and so on. For elements with equal n+l, that with the lowest n comes first.
This rule works wonderfully most of the time, but there are exceptions: for example, the pause in filling of the d orbitals while the outermost s orbitals are filled for chromium and molybdenum. It’s easy enough to rationalise those anomalies, but for the f block things get trickier. Take thorium. Its electronic structure beyond the radon closed-shell core is 6d27s2: it has no 5f electrons at all in its ground state! What is it doing in the f block? But it would be absurd to put it anywhere else – it’s easily accepted there as an anomaly.
A similar inconsistency clouds the question of which pair of elements claims the places in group 3, for none of the element candidates (La, Ac, Lu or Lr) has partially filled f orbitals either. Lanthanum and Ac have configurations [Xe]5d16s2 and [Rn]6d17s2 – and so, with their partially filled d shells, might lay claim to be d block elements. But wait: Lu also has that claim, with configuration [Xe]4f145d16s2! What of Lr? It seems to be different again; relativistic calculations have suggested that its outermost electron goes not into a 6d orbital but into 7p, and recent experiments on this very short-lived element seem to confirm this, indicating that it has a surprisingly low first ionisation potential.5Doesn’t that weaken its claim to be a d block element?
Some think so. Others say that Lr might instead be regarded as simply another anomaly: a d block element with no outer d electrons. That might seem like special pleading, but not necessarily. Consider what the alternative of putting Lr and Ac in the d block entails: either the f block has to be placed before the d block (which disrupts the steady progression of atomic number, and so seems indefensible), or the f block must be interposed between group 3 and the rest of the d block, which seems awkward at best. What’s more, this arrangement would then disrupt vertical trends in several chemical properties, such as atomic radius and melting point.1 Besides, Lu has physical and mechanical properties resembling those of transition metals6 – although whether it is chemically more akin than La to Sc and Y is less clear.7
A task group,8 of which I have been asked to be a member, now aims to solve the problem. We hope to make a recommendation to the International Union for Pure and Applied Chemistry (Iupac) after consultation and discussion, for which comments and suggestions are most welcome.
Editor: If you have any views on what belongs in group 3, get in touch at firstname.lastname@example.org – we’ll pass them on.
1 W B Jensen, J. Chem. Ed., 1982, 59, 634 (DOI: 10.1021/ed059p634)
2 L Lavelle, J. Chem. Ed., 2008, 85, 1482 (DOI: 10.1021/ed085p1482)
3 W B Jensen, J. Chem. Ed., 2009, 86, 1186 (DOI: 10.1021/ed086p1186)
4 L Lavelle, J. Chem. Ed., 2009, 86, 1187 (DOI: 10.1021/ed086p1187)
5 T K Sato et al., Nature, 2015, 520, 209 (DOI: 10.1038/nature14342)
6 N Settouti and H Aourag, J. Min. Met. Mater. Soc., 2015, 67, 1247 (DOI: 10.1007/s11837-014-1247-x)
7 W Leal, G Restrepo and A Bernal, MATCH Commun. Math. Comput. Chem., 2012, 68, 417
8 E Scerri, Chem. Int., 2016, 38, 22 (DOI: 10.1515/ci-2016-0213)