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The world's most famous table: 150 years of Periodic Law

Periodic table
150 years ago this month, Russian chemist, Dmitrii Mendeleev, first presented his idea to organise all the known elements into a handy table according to their atomic number, electrons and properties. Periodic Law, as he called his system, transformed science.

Mendeleev’s system became a vital tool to anyone studying or researching across many scientific fields. The ingenious thing about the periodic table first presented by Medeleev, was that it could also predict the future. He left gaps for five mystery elements he knew must exist but had not been discovered yet. They were discovered and they did fit broadly in the spaces he had left for them. He enabled scientists to continue to add to the table and throughout the next 150 years his idea was expanded and developed. A further 55 elements have been discovered and added since Mendeleev first devised his system.

Now, the iconic Periodic Table is displayed in schools and is known to school children the world over – there is even a song to go with it.

The United Nations has designated 2019 as the International Year of the Periodic Table to celebrate "one of the most significant achievements in science".

Here, scientists from the University of Warwick select from the Periodic Table, some of the most important elements to them.

The precious metals

Professor Peter Sadler, Professor of Chemistry and Dr Cinzia Imberti, research fellow in the Department of Chemistry


Ruthenium, osmium, rhodium and iridium are rare metallic elements located in the second and third rows of the transition metals, in groups 8 and 9. Together with their more famous cousins, palladium, platinum, silver and gold, these elements belong to the precious metals family. The preciousness of these elements is generally connected to their high economic value (they are often traded as ingots in markets), but their potential use in medicine makes them even more valuable.

Platinum as the drug Cisplatin has been in clinical use to treat cancer for over 40 years, and the use of gold to treat rheumatoid arthritis dates back over 80 years as injectable Myocrisin and over 30 years as the oral drug Auranofin. Two more platinum drugs Carboplatin and Oxaliplatin are also widely used. These precious metals have different chemical properties compared to elements commonly found naturally in the body (in terms of their oxidation states, coordination numbers and geometries). They provide new mechanisms of action that are not accessible to ordinary organic molecules, and can fight resistance, a serious clinical problem.

In the Sadler group, we work on catalytic organometallic anticancer agents based on ruthenium, osmium, rhodium and iridium. Our hope is that such catalysts, at minute doses, will be effective in destroying cancer cells, as well as active against resistant cancers. We also focus on platinum and iridium complexes which are relatively harmless until ‘switched on’ by light (photochemotherapy), so it enables us to control their chemotherapeutic activity in space and time and minimise side-effects, a key issue for current clinical anticancer drugs.

Gallium - one of Mendeleev's 'missing' elements

Professor Richard Walton, Professor of Chemistry

Gallium is a tremendously important element in the history of the Periodic Table, since it was not known at the time Mendeleev put together his first version of the table in 1869, but with great intuition he left gaps for ‘missing’ elements based on the patterns he observed in atomic masses. He went further and predicted the properties of the absent elements. Gallium was one of these absences and just a few years later in 1875 it was discovered in France, named to commemorate the country of its discovery: this not only filled a gap in Mendeleev’s table, but also possessed its predicted physical properties. This helped to validate the idea of a Periodic Table and was part of the reason it became adopted so widely and so quickly.

Gallium has unusual properties: although it sits just beneath the familiar metal aluminium in the Periodic Table and is also a metallic element, it melts at just less than 30 °C. It then remains a liquid until over 2200 °C, the largest liquid range of any chemical element. One application of gallium relies on this property, in alloys in high-temperature thermometers, where it replaces toxic mercury. Gallium also finds applications in semiconductor technology: for example, gallium arsenide is used in logic chips and light emitting diodes in electronic devices.

In my own work in materials chemistry, compounds of gallium have been a focus since my first research project as an undergraduate. Then I was working on preparing artificial versions of aluminium-containing zeolites that are used for many applications, ranging from industrial catalysts, to water purification in the environment. Here, the differences between the chemistry of aluminium and gallium allowed for new crystalline structures with unique properties. In the past few years in Warwick in our research into various inorganic materials we have been examining even simpler compounds of gallium, its oxides. Using new synthetic chemistry approaches, in some cases making use of the low melting point of metallic gallium, we have developed novel approaches to new forms of gallium oxides. This is topical since gallium oxide semiconductor devices are presently emerging as candidates for future generations of electronics, overcoming some of the limitations of silicon, and are attracting global attention. This is a topical field of interdisciplinary research that overlaps with physics and materials engineering, taking fundamental chemistry into functional materials.

Iron - nature's catalyst and driver of technological advancement

Professor Tim Bugg, Professor of Biological Chemistry

Rusty wall

Iron (Fe) is so useful to humans - we use it to make metal objects like cars, ships, buildings, gates & door-stoppers. But nature uses it to catalyse some amazing reactions in biochemistry.

My research group works on enzymes, particularly enzymes involved in the breakdown of lignin, a polymer found in plant cell walls. We are trying to convert lignin into renewable chemicals so we need to understand the action of these enzymes. For many years my group used to work on catechol dioxygenases, a group of enzymes that catalyse using molecular oxygen as a reagent, and an iron(II) cofactor in the enzyme active site. This is an amazing reaction that you can’t do in the chemistry laboratory, and yet these enzymes catalyse these reactions with no special requirements - at neutral pH and at room temperature. We spent many years working out exactly how these enzymes worked, and trying to make chemical models to mimic their reactivity.

More recently we have discovered a class of enzymes in bacteria that can oxidise lignin, which is an even more difficult task, because lignin is not susceptible to hydrolytic breakdown and it’s usually insoluble and inert. We have identified a class of enzyme in specific bacteria called dye-decolorizing peroxidases that can oxidise lignin. These enzymes also use iron, but in a heme cofactor – similar to what is used in haemoglobin to transport oxygen in the blood.

We’re currently trying to use these enzymes, and other oxidative enzymes that use manganese (Mn) and copper (Cu), to break down lignin and make useful chemicals such as bioplastics.

Dr Joanna Collingwood, Reader in the School of Engineering

I also choose Iron. It’s the most abundant element on Earth by mass, and the fourth most abundant element in the Earth’s crust. From some perspectives, it is the most stable element known to humankind. It is essential to life as we know it, essential in humans for oxygen transport and cellular respiration, yet toxic to these same life-forms if mishandled. Iron enables us and other species to navigate; the iron oxide magnetite was used as a compass – lodestone - by some of the earliest known armies and sailors, while magnetotactic bacteria grow an internal compass of magnetite particles to determine their orientation in the Earth’s magnetic field.

From the Iron Age to the present day, use of iron has been integral to technological advancement. In pure form it will rust indefinitely where it stands exposed to air and water, flaking away, undermining structure, distracting with its beauty, colouring rocks and soil with a rich palette that since the earliest times has been used to decorate homes and treasured possessions. In impure forms, alloyed with the tiniest quantities of carbon and other metals, iron produces some of the strongest, most durable and workable material we have at our disposal.

Our community harnesses knowledge and skills from across the disciplines to understand the role of iron in life on Earth, in the life of plants and animals, in human health and disease. If we look beyond Earth, the surface of our neighbour Mars is red with iron-oxide; in the galaxies above, billions of supergiant stars are transforming irreversibly into cores of iron.

The rare earth metals

Dr Monica Ciomaga Hatnean, Senior Research Fellow in the Department of Physics


My favourite chemical elements are the rare earth metal series from Lanthanum to Lutetium, Yttrium and Scandium. These elements are rather reactive and very difficult to obtain in their pure form because, due to their similar properties, several rare earth metals can be extracted from the same substance or mineral. Even though they are called rare earth metals, they can be found in many aspects of our daily lives.

Rare earth metals and their chemical compounds have a wide range of applications. We use them in lasers, magnets, electric motors in hybrid vehicles, nuclear reactors (as control rods), medicine (including in Magnetic Resonance Imaging), computer memories, camera lenses and electron microscopes.

My research work involves the study of crystals of materials with exotic physical properties (magnets, superconductors, topological insulators, etc) and the majority of the materials that I work with are rare earth-based compounds. I believe that, due to their intriguing properties and high potential for technologies, rare earth metal compounds will continue to be one of the most studied and most promising family of elements in materials science and engineering.

Cobalt on your cornflakes

Professor David Haddleton, Professor of Polymer Chemistry


Cobalt is both important to my research in making new polymers but also, believe it or not, as an ingredient in my cornflakes!

Cobalt is a transition metal, which means it can exist in different oxidation states and this can make it really important in catalysis. As a transition metal it can also be classed as a ‘heavy metal’ which I think gets it a bad press as this starts people thinking “Oh my goodness that must be toxic”.

On the contrary, out of the 181 atoms in vitamin B12 the one cobalt atom is the star of the show and the other 180 are just there to present the cobalt in the best possible way – just like all supporting roles. Vitamin B12 is the most complex of all vitamins and it might surprise most people that it’s a heavy metal that is essential for its use. Vitamin B12 is present in every cell of our body and is a crucial part of metabolism and the functioning of the nervous system. We cannot produce vitamin B12 as only certain bacteria in soil can do this so we must get it from food. It is such a good catalyst that we only have about 5 mg (that’s 0.05 g) in our body and yet it is in every cell. It is very stable and not prone to decomposition so we only need to replenish about at 0.002 g per day. The ingredient ‘cobalamin’ listed on the back of your cornflake packet is part of the 0.002 g required every day.

In the 1970’s a Russian chemist decided to see what Cobalt would do if you added it to a free radical polymerisation and found it had remarkable properties in the right circumstances. I came across it when I worked in industry at what was an important UK company at the time, ICI. I was looking at new ways to make poly(methyl methacrylate) – often known as Perspex. This polymer is used in many things such as plastic rulers, backlights of cars, shopsigns and all aircraft windows and indeed it was first used in Spitfire cockpits in WWII – a true UK invention.

When added in really minute quantities it acts as a chain transfer agent (reduces the molecular weight of the polymer) and we successfully used this to make inks used today in pretty much all glossy magazines, eliminating the need for harmful organic solvents in the process.

Over the last 25 years at Warwick we have continued to work on this chemistry (cobalt catalytic chain transfer polymerisation) which has led to many PhD theses and academic publications. Currently our work is diverse and wide-ranging and includes improving pesticide delivery, improving automotive lubricants in engine oil and gear box oils, dispersants in paints and developing new inks and coatings.

Europium – The real spin doctor

Dr Paolo Coppo, Senior Teaching Fellow in Chemistry

Europium is one of the least abundant elements in the universe, yet reasonably abundant on the Earth’s crust.

Europium’s special qualities lie in the arrangement and behaviour of its electrons. We can imagine electrons like orbiting particles, around a central nucleus. But how fast does an electron move? It depends on the charge of the atomic nucleus and the distance from it.

In heavy atoms, electrons orbit very fast, to avoid collapsing in the nucleus, and no more so than in lanthanoids like europium. Fast electrons couple their orbit and spin momentum in a 'total angular momentum" just like a spinning ice skater bringing their arms and legs into their body to increase their spinning speed.

Spin-orbit coupling has fascinating consequences – the ‘excited’ states emit light – these emissions can give a detailed insight of the environment experienced by the atom. The red light emitted by Eu (III) is used in diagnostics and electronics such as fluorescent lights and LEDs.


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