Elements

In the final programme in our Elements series, Justin Rowlatt looks at the rarest and oddest members of the periodic table. Selenium, bismuth, molybdenum, antimony, rhenium, hafnium, zirconium, tellurium, thallium, barium. What are they? And what are they used for?Minor metals merchant Anthony Lipmann explains how he made a fortune tracking down a stockpile of one toxic element sufficient to kill millions of people - and sold it to Japanese camera manufacturers.We set chemistry professor Andrea Sella a musical challenge to round off his elucidation of the periodic table, going out with a pyrotechnic bang.And cosmologist Martin Rees explains why 85% of the matter in the universe isn't made up of chemical elements at all, but instead of "dark matter", whatever that is.(Picture: Elements series planning board; Credit: Laurence Knight/BBC)

This radioactive metal holds the promise of thousands of years of energy for the world. But is it really any cleaner or safer than traditional uranium-based nuclear power?Chemistry Professor Andrea Sella of University College London takes the helm, as he speaks to no less than three nuclear physicists in his quest to discover whether thorium will deliver that godlike bolt of electricity, or just remain a nebulous dream.Prof Bob Cywinski of the University of Sheffield is a fan, whereas Dr Arjun Makhijani of the Institute for Energy and Environmental Research is decidedly not.Meanwhile India presses ahead with its now 60-year-old thorium energy programme, as former nuclear chief Anil Kakodkar explains.(Picture: Human hand holding lightning; Credit: Sergey Nivens/Thinkstock)

The macabre poison we know from crime novels and history books has some surprising modern uses.Justin Rowlatt travels the Subcontinent - first to India's Forest Research Institute in the Himalayas where Sadhna Tripathi explains why the chemical element ends up in telegraph polls.We then head to Bangladesh, scene of the "largest mass poisoning in history". Justin speaks to Dr Quazi Quamruzzaman who helped first uncover it, and to Richard Pearshouse of Human Rights Watch, who says the problem still hasn't gone away. Sanjay Wijesekera of Unicef explains how the road to this particular hell was paved by good intentions, and how his aid agency is helping to guide Bangladesh back out again.(Picture: Bangladeshi woman's foot showing lesions caused by arsenic poisoning; Credit: Majority World/UIG via Getty Images)

Why does iodine deficiency still blight children in developing countries like India?Justin Rowlatt travels to Dehradun in the Himalayas with world expert Chandrakant Pandav to diagnose schoolchildren still suffering from the throat swelling called goitre, and from the permanent mental retardation known as cretinism.Justin challenges Indian government officials to explain why, 50 years after India first introduced its salt iodisation programme, this easily solvable problem still persists. (Picture: Woman with large goitre; Credit: Dr P Marazzi/Science Photo Library)

This toxic metal is slowly being phased out of our lives. But as presenter Justin Rowlatt discovers, while nickel-cadmium batteries may have disappeared from our gadgets, they still help to keep planes up in the air.Chemistry professor Andrea Sella tells the story of this colourful yet poisonous element, while metals consultant Dominic Boyle says even if we stop using it all together, the stuff is still piling up.Justin visits the offices of SES Batteries in the Indian military town of Ambala to find out why the country's army still uses nickel-cadmium batteries. And Jennifer Holdaway of the Social Science Research Council explains how cadmium found its way into China's rice supplies.(Picture: Stack of AA nickel-cadmium batteries; Credit: Sergei Chumakov/Thinkstock)

Is the dream of a hydrogen-fuelled zero-carbon economy achievable? Presenters Justin Rowlatt and Laurence Knight ask where the hydrogen will come from and how we will store it. Professor Andrea Sella of University College London blows up a hydrogen balloon, while Professor James Durrant of Imperial College explains what an artificial leaf is. In India, Alok Sharma of the Indian Oil Company gives a tour of their hydrogen refuelling station and fuel cell research centre. And Ned Stetson of the US Department of Energy explains why the vexed problem of containing all this hydrogen is forcing them to resort to "complex anions" and other obscure chemistry.(Picture: An Iwatani serviceman refuels a Toyota Mirai car with hydrogen in Tokyo; Credit: Yoshikazu Tsuno/AFP/Getty Images)

As climate change threatens to play havoc with the rain, could we instead draw our water directly from the ocean? In his second gulp of H2O, presenter Justin Rowlatt hears from climatologist Raymond Pierrehumbert about how global warming is causing drastic but often unpredictable disruption to our natural supplies of freshwater. Yet as Israel enters its third year of dought, few of the country's citizens are aware of any water shortages. The BBC's Shira Gemer reports on the technological breakthroughs that have made this possible - from the gigantic Sorek desalination plant, to the drip irrigation pioneered by Netafim in the Negev desert. We also hear from desalination expert Raphael Semiat of Technion University how much the rest of the world can emulate Israel's success. (Picture: Icebergs float in the Jacobshavn Bay in Greenland; Credit: Uriel Sinai/Getty Images)

Neon, argon, krypton and xenon: Laurence Knight investigates their uses, from the blinding light of the arc welder's torch to the dying trade of the neon sign-making. Professor Andrea Sella explains how an alumnus of his home University College London - Scottish chemist Sir William Ramsay - uncovered an entire column of the periodic table containing all of these unreactive gases. Neon sign-maker Graham Cox shows how to bring colour and light to the dingiest of corners, while neon artist Marcus Bracey welcomes us to his gallery, God's Own Junkyard, where he insists the future for these gaseous elements remains bright.(Picture: “Find Love Upstairs” artwork by Chris Bracey at the God’s Own Junkyard neon art gallery)

Radium, polonium and radon may be names to make your hair stand on end, but are they actually useful for anything? And is our fear of them overbaked? Laurence Knight gets the chemistry rundown from Prof Andrea Sella of University College London at a hospital that used to treat cancer with radiation. Al Conklin of the Washington State Department of Health explains how we are still dealing with the world's early Twentieth Century craze for all things radioactive. Edwin Lane reports from Finland on how the country's geology and climate conspired to fill their houses with a radioactive gas. Plus, we hear from Prof Norman Dombey, a key expert witness in the public enquiry into the murder of Alexander Litvinenko.(Picture: Glow-in-the-dark radium clock dial; Credit: Ted Kinsman/Science Photo Library)

Rare and toxic, beryllium can do serious damage to your lungs. Presenter Laurence Knight explores whether and how we can make use of this metal safely. Prof Andrea Sella of University College London explains why beryllium's surprising scarcity is the very reason it can be so harmful to the body. Gianna Palmer reports from the Hanford nuclear site in Washington State on this chemical element's intimate and poisonous history in the US nuclear weapons programme. And we hear from IBC Advanced Alloys, a company that claims to have a novel, cheap - and safe - way of producing aeroplane parts out of beryllium-aluminium. Image: A man holding a shockproof X-ray tube - Beryllium is used in the construction of these. Credit: Douglas Miller/Topical Press Agency/Getty Images

Titanium is the magic metal that made possible the mass production of plastics and paints, as well as buildings that clean both themselves and the air around them. Presenter Laurence Knight heads to the Ineos oil refinery in Grangemouth, Scotland, to see how just a smidge of a titanium-based catalyst transforms a type of natural gas into the stuff of food packaging, bottles and car bumpers. He hears from Prof Andrea Sella why most of us spend our lives surrounded by titanium without even realising it. And Brian Pickett of pigments manufacturer Cristal explains why his company has been painting various bits of London to further the fight against city smog. (Picture: Window cleaner; Credit: Peter Parks/Getty Images)

Why is oxygen essential to steelmaking, how do you extract it from the air, and can you inhale too much of it? Answering these questions leaves presenter Justin Rowlatt almost breathless. Prof Andrea Sella demonstrates the convenience and power of this bulk chemical, whilst Laurence Knight heads to BOC's air separation unit in Fawley to see how it is mass produced. Meanwhile Justin climbs a mountain, scuba dives and pedals like mad on an exercise bike inside a low oxygen chamber. But it's all in the name of science, as husband-and-wife medics-cum-mountaineers Denny Levett and Mike Grocott explain.

The “element of life” also makes the air that we breathe a perilous and costly atmosphere in which to operate. Prof Andrea Sella of University College London provides presenter Justin Rowlatt with a characteristically striking argument for why oxygen is so “incredibly dangerous”, and how its advent turned Planet Earth into a snowball. Pawanexh Kohli, in charge of India’s national cold chain strategy, explains over a cup of chai why the oxygen needs of fresh vegetables and fresh meat are very different. Physics polymath Baldev Raj unpicks the mystery of Delhi’s 1,600-year-old iron pillar, and explains just how damaging rust and corrosion can be. And former “smoke-jumper” Frankie Romero explains the mesmerising attraction of wildfires, and why stamping them out isn’t always a good idea. (Photo: Wildfire in Los Alerces National Park, Argentina; Credit: Emiliano La Salvia/AFP/Getty Images)