The Women Who Set the Table

Many women have contributed to the periodic table and the understanding of the chemical elements... Can you name them?

Everything on Earth is made up of smaller building blocks called ‘elements’. To date, 118 different elements have been discovered, and 150 years ago a special table was put together containing all the known elements at that time. Over the following decades there was a surge in chemistry research, and many scientists raced to discover the remaining elements and secure their name in the history books.

In the early 20th century, subjects like chemistry and physics were male dominated and women were rarely acknowledged for their work. Women were often forbidden to speak at scientific meetings, or even hold a position within the university. This meant that during this prolific time for chemistry, many women were not recognised for their notable contributions to the periodic table, and so have been lost in the records. The Royal Society of Chemistry attribute the discovery of four elements to female scientists. To celebrate 150 years of the periodic table, along with International Women's Day, this article highlights the important contributions from a few of the world’s most outstanding female scientists.

Marie Curie - Discovered polonium and radium

Arguably the world’s most famous female scientists is Marie (Skłodowska) Curie, a Polish chemist and physicist who set many ‘firsts’ in her career. In 1903, she was the first woman to be awarded a Nobel Prize, one of the most prestigious awards in science, shared with Antoine Henri Becquerel and her husband Pierre for their contributions to physics. Becquerel had noted strange rays coming from the element uranium, and together they discovered a new property of elements that would later be known as ‘radioactivity’. Curie is attributed with coining the phrase, and the realisation that the radiation was a result of the atom itself paved the way for a whole new field of science.

Each element is made up of one type of atom, and atoms themselves have three main parts - protons, neutrons and electrons. In the centre, the nucleus, there are the positively-charged protons and uncharged neutrons. To balance the positive charges, moving around the nucleus are layers of negatively-charged electrons. Some elements are thought of as ‘unstable’ because their core is imbalanced. These unstable elements occur naturally in the Earth’s crust, but their nuclear instability means that, in an attempt to reach a stable state, they are constantly breaking down, or decaying. This releases energy as radiation. It tends to be the heavier elements that are radioactive, as they have bigger nuclei and this makes them more unstable. Radioactive decay is a random process, and the discovery of the phenomenon is what first put Curie’s name into the history books. The study of atoms breaking up from radioactive decay allowed scientists to piece back together the atoms, and therefore better understand how they are structured.

Fascinated by this new area of chemistry, Curie and her husband began the quest for the missing elements in the periodic table. A mineral ore commonly known as pitchblende is a source of the radioactive element uranium. Solid ores are found in the Earth’s crust and are a complex mixture of many elements. They often contain valuable elements that cannot be mined by themselves. Curie noticed that the levels of radiation in the pitchblende ore were far higher than could be accounted for on the basis of uranium alone. In 1898, after sifting and refining tonnes of ore, they discovered two new radioactive elements - polonium, named after Marie Curie’s native country Poland, and radium, the most radioactive element ever discovered.

Today polonium is used to power many of the spacecrafts and rovers sent on exploration missions. As the element decays, it reaches very high temperatures, around 500°C, and so acts as an energy source for technology in space. In 2006, this highly toxic element was also used to poison the late Russian agent Alexander Litvinenko. Radium was famously used to paint the hands and dials of watches due to its self-luminescence, or glow-in-the-dark, properties. This radioactive paint was used as late as the 1960s, after which safer materials were adopted, once the dangers of radium were realised.

1911年居里,那时一个寡妇,被授予chemistry Nobel Prize for these discoveries, making her the first person, and only woman, ever to win two Nobel Prizes. She also remains the only person to win a Nobel Prize in two different sciences.

Sadly, with radioactive elements being newly-discovered, the dangers of the elements were unknown. Curie worked unprotected with these hazardous materials and her death is widely believed to be a result of long-term exposure to radiation. To honour her legacy, another radioactive element, discovered years after her passing, was called curium. There also exist three radioactive minerals bearing parts of her maiden and married names: curite, sklodowskite, and cuprosklodowskite. In 1910, a unit of measuring radioactivity was defined and named the ‘Curie’ in honour of the couple's contribution to this new area of science. Their daughter Irène Joliot-Curie followed in their scientific footsteps and was later awarded the Nobel Prize in Chemistry in 1935 for the discovery of artificial radioactivity alongside her husband Frederic Joliot-Curie.

Ida Noddack - Rhenium

In 1925 German chemist Ida Noddack isolated a new element from an ore called gadolinite in which the element was an impurity. This work was carried out alongside her husband Walter Noddack, and Otto Berg. Together they called it ‘rhenium’ after the river Rhine that runs through Germany. This new element filled one of the two spots that were vacant in the Periodic table, below manganese. It is one of the rarest elements in the Earth’s crust and today can be found in the metal alloys, or metal mixtures, that are used to build jet engines.

The team tried hard to fill the other vacant spot above rhenium, and even claimed to have discovered it, but the experiments were irreproducible and the findings were dismissed by the scientific community. Despite this setback, Noddack remained focused on the chemistry, and even challenged a widely-believed theory at the time, disputing a paper by Enrico Fermi and arguing that elements could be broken down into smaller fragments. But as she had no experimental proof, her theory was mocked.

In time, her arguments were shown to be correct, and the concept she proposed later became known as ‘nuclear fission’. On this basis, Noddack is acknowledged as the founder of this branch of chemistry. In this process, a neutron bombards a heavy element, such as uranium, which causes the atom to split into smaller fragments and a large amount of energy is released. This process leads to a chain reaction of nuclear fission, and this excess power and heat can be captured in a reactor. When this reaction is controlled we can generate electricity, as is the process in nuclear power plants. On the other hand, an uncontrolled fission reaction is the basis for the power and destruction of nuclear weapons and atomic bombs.

Marguerite Perey - francium

When the periodic table was first proposed in 1869, gaps were left for the elements not yet discovered, but predicted to exist. There was a gap below the highly reactive caesium, which was filled in 1939 by Marguerite Perey’s discovery. While working in the same institute as Marie Curie, Perey discovered a new radioactive element which she named francium, after her home country of France. This is the only element that was discovered solely by a female scientist. The lifespans of radioactive elements are difficult to determine since the elements are so unstable and the process is random. Instead scientists can estimate the half-life of an element, which is the time taken for the radioactivity of an element to have fallen to half its original value. Francium is so intensely radioactive its half-life is only 22 minutes! Perey continued her career, achieving many great feats. She was the first female to be become the Chair of Nuclear Chemistry at the University of Strasbourg and the first woman to be elected as a corresponding member of the French Academy of sciences. Sadly like others working with radioactive elements before her, she died of radiation related causes.

Lise Meitner - Fission Research

The idea of nuclear fission had already been suggested by Ida Noddack, but was largely ignored by her fellow scientists. Austrian physicist Lise Meitner was part of a team who examined the experimental data, and her reasoning and calculations helped form the theory of nuclear fission. Finally there was evidence that the atomic nucleus could be split into smaller nuclei and these results were published in 1939, but without Meitner’s name on the paper. The work was awarded the 1944 Chemistry Nobel Prize, but the sole recipient, Otto Hahn, did not acknowledge Meitner’s contribution to the discovery, even though her calculations convinced him of the phenomenon. A later-discovered element was called meitnerium though, in honour of her contribution to radioactive science.

Meitner is nonetheless acknowledged for the discovery of an isotope of the element protactinium. Isotopes occur when the atoms of an element have the same number of protons, but a different number of neutrons, essentially the same element just different masses. This change can have a massive effect on the half-life - the time taken for an element to decays by half of its original mass - of radioactive elements. For example the isotope protactinium-234 has a half-life of 6 hours and 42 minutes, but the isotope that Meitner helped discover (protactinium-231) has a half-life of 32,500 years! Small changes can make a large difference to the elemental properties.

The Female Legacy

Many other great female scientists, like Austrian physicist Berta Karlik and Polish chemist Stefanie Horovitz, helped shape the periodic table and enriched our understanding of the elements. Through the decades, female scientists have had to break down many barriers in order to be taken seriously and have their research valued. The women mentioned throughout this article, along with many others, have paved the way for future generations of female scientists.

In 2013, school students were asked to describe a scientist and more than 85% of girls and almost all of the boys drew men. This statistic highlights the lack of visible female scientists, and could be influencing the career choices of children. Hopefully now you can name more than one female scientist and realise that their prominence could inspire generations to come. It is vital that we acknowledge the potential of all scientists - regardless of gender or any other discriminating factor - and realise that their contributions to science could revolutionise our future...

“Don’t be afraid of hard work. Nothing worthwhile comes easily. Don’t let others discourage you or tell you that you can’t do it. In my day I was told women didn’t go into chemistry. I saw no reason why we couldn’t.”– Gertrude B. Elion, Nobel Laureate