Trish McAlaster/The Globe and Mail
What's an element?
For the ancient Greeks, there were four of them – earth, air, fire and water. That idea turned out to be far too simple to explain the diversity of matter we encounter in everyday life. But the basic premise that matter is composed of a finite list of key ingredients is sound. Today, we know that much of the matter that we're made of is in the form of different types of atoms. The periodic table is a list of those atoms, one for each square, in order of increasing mass.
No. 1 on the list is hydrogen, the lightest element in the universe. Its nucleus is composed of one positively charged particle known as a proton that's orbited by one negatively charged electron. An element's position on the table is simply the number of protons it contains. Adding more protons to a nucleus makes it a new element with new chemical properties. A third kind of particle, the neutron, has no charge, but its presence is what keeps elements that are heavier than hydrogen stable.
How nature makes elements
Because like charges repel, all protons contained within an atom's nucleus are constantly pushing each other apart. Atoms don't disintegrate because there is a stronger force – literally called the "strong force" – that can hold protons together at short range. But it takes energy to push protons together to a point where the strong force can take over to make elements that are heavier than hydrogen.
When the universe began in a cosmic inferno known as the Big Bang, there was plenty of energy to go around. Essentially all of the hydrogen there was created in the immediate aftermath of the Big Bang. A portion of it was then turned into helium, along with a smattering of other light elements. Millions of years later, when the first stars began to shine, the nuclear reactions within those stars provided the energy to create carbon, nitrogen, oxygen and so on up the periodic table. Any atoms heavier than iron can only be forged in a supernova – the explosive death of a massive star.
Setting the table
By the 1860s, there were 53 known elements. The Russian chemist Dmitri Mendeleev realized that these elements can be arranged in a table of increasing weight that grouped elements together with those that shared similar properties. Thus, bromine, element No. 35, lines up with the much lighter chlorine, because they behave quite similarly in chemical reactions. These recurring similarities are what make the table "periodic."
Mendeleev claimed to have first seen the table in a dream. Although others had noticed the recurring properties of the elements, it was his insight, first presented in 1869, that caught on. The periodic table was born. Mendeleev famously predicted that holes in the table represented elements that had not yet been discovered. A few years later, one of those gaps, located right below aluminum, was filled when chemists verified the existence of the metal known as gallium.
As atoms get heavier, it's harder to keep all of the protons together – and at higher masses, elements tend to decay radio-actively into lighter elements. The heaviest element found in nature in significant quantity is uranium.
In the pioneering days of nuclear physics, researchers at the University of California Radiation Laboratory in Berkeley realized they could make new elements by bombarding a uranium target inside a particle accelerator. The first two synthetic elements were named neptunium and plutonium, after what were then the only two known planetary bodies in the solar system that orbit beyond Uranus. They were both discovered in 1940, but because of the secrecy surrounding nuclear research during the Second World War, the existence of plutonium was not disclosed until 1948.
The same research team went on to create several more new elements, launching a new era in atomic and chemical research.
Canada's strongest historic connection to the periodic table is arguably through element No. 104, rutherfordium. First produced in the 1960s in laboratories in the United States and the Soviet Union, priority for its discovery was not settled until 1997.
The element is named after the father of nuclear physics, Ernest Rutherford. Born in New Zealand, Rutherford arrived at McGill University in Montreal in 1898. There he began a series of landmark experiments on radioactive elements. It was Rutherford who first realized that radio-active decay involved one element changing into another. He also came up with the concept of a half-life, the length of time it takes for half of any amount of a radioactive substance to decay. After nearly a decade at McGill, Rutherford moved to the University of Manchester in Britain. In 1908, Rutherford was recognized for the discoveries he made while in Canada with a Nobel Prize in chemistry.
Climbing the table
Since 1940, scientists have continued to work on synthesizing new elements in an effort to study their properties and glean insights into the behaviour of the heaviest atoms. In one sense, this is pure, exploratory science with no particular end in mind other than to see what can be achieved with current technology and to gather new knowledge. In another sense, though, the quest to create new atoms is highly competitive. Each time a new milestone on the table is reached, the scientists that get there first win the right to name the new element they make. When two or more labs claim a new element, it can take years to sort out who has priority.
Today, only a few facilities in the world have the capability of producing new elements by smashing atomic nuclei together at high speed. This has set the stage for an elite race between labs based in different countries, like teams of elite mountain climbers racing up a challenging peak. In such a contest, national as well as scientific prestige is on the line.
The gang of four
In recent days, the International Union of Pure and Applied Chemistry, the body that oversees the table and its nomenclature, announced it has accepted the discovery of four new elements, the first additions to the periodic table since 2011.
The elements – Nos. 113, 115, 117 and 118 – plug a couple of gaps in the table that were created by the earlier synthesis of flerovium and livermorium. They also complete the seventh row of the periodic table. While completing the row is more of a symbolic achievement than anything else, it includes the first new addition of a halogen (the family of elements related to fluorine and chlorine) since 1940, and the first new noble gas (the family related to helium and argon) since 1898. The periodic table has never looked as tidy as it does today.
The new elements only last for milliseconds. Their nuclei contain so many protons, they basically fall apart almost as soon as they are made. Under such conditions, it's not easy to know if a new element has actually been created. The evidence has to be accumulated after many attempts and is based on the detection of longer-lived decay products.
All of the four new elements have been claimed by different groups for years, in some cases going back to 2004. Only now has the union determined that the evidence is sufficient to validate the four claims and assign priority for the discoveries.
Element 113 is interesting because its discovery has been credited to a Japanese team. This is the first Asian group that will add a new name to what has until now been a decidedly Eurocentric periodic table. The other three elements were created by a collaboration of U.S. and Russian research teams, a somewhat tricky situation, since the naming rights cannot be evenly divided between the two countries. The teams have about five months to submit their candidate names, which, according to current rules, can refer only to a mythological concept or character, a mineral, a place or geographical region, a property of the new element or a scientist.
For now, no group has claimed to have created any element beyond 118, but efforts to do so are ongoing. One tantalizing possibility that is helping to drive the effort is that at still higher positions up the periodic table, there could be elements with nuclei that are structured in such a way that they can persist for much longer than a fraction of a second. The theory, first proposed in the 1960s, suggests a group of very heavy but long-lived elements may exist like islands in a sea of instability. Whether such fabled islands can actually exist remains a matter of debate. Very heavy atoms that last a long time would be useful for all sorts of scientific applications if they turn up in future.
The periodic mirror
When it comes to organizing a vast amount of scientific information in a compact way, it's hard to beat the periodic table. Its elegance has transcended chemistry and physics, and inspired great works of literature and art. The celebrated neurologist and author Oliver Sacks, who died last year of terminal cancer, wrote eloquently of how he associated each year of life with the corresponding element on the table. He made it to lead – No. 82, a particularly long-lasting element.
Our collective fascination with the table and its future has deep roots. Hidden within it is the message that we live in a universe well tuned to generate the building blocks of matter and life. Much of that universe is as simple and dull as hydrogen gas. But in a few corners, the universe has managed to sweep together some handfuls of more substantial stuff to form planets, organisms and civilizations.
We call it a table, but look past the funny little boxes and you'll see a reflection of everything that atoms can do and dream.