Francium is an extremely rare and unstable element that is placed in Group 1, Period 7 of the Periodic Table. It is a radioactive element and is an alkaline metal. It is also the last discovered natural element.

When Mendeleev came up with the Periodic Table of the elements, he correctly deduced that there were many elements that were still to be discovered (or synthesized). So he incorporated gaps in his periodic table so that new elements could be accommodated in the future. As the elements were still to be discovered, he gave these yet-to-be-discovered elements temporary names. If the yet to be discovered element had the atomic number that would place it just one period down the already discovered element, it was termed as Eka- followed by the name of the already discovered element. 

A Brief History of Francium

Taking it forward from where we left above, if the yet-to-be-discovered elements were to be placed two or three periods down the already discovered element, they would be given a suffix of dvi and tri respectively and then the already discovered element’s name will follow. For example, Mendeleev predicted the existence of the element that would occupy the box just below Aluminium. Hence he named the potentially discoverable element as eka-Aluminium. Today we know the element as Gallium. Eka, dvi and tri are the Sanskrit words for one, two and three.

Eka-Caesium: The Temporary Name Given to Francium

Just like Mendelev predicted that there were elements that were yet to be discovered, many other scientists did that too. As time progressed, scientists realised that there should be an element just below Cs. Hence, it was temporarily known as eka-Cesium until its discovery.

Why Scientists Expected The Existence of A New Element Below Caesium: Radioactive Displacement Law

In the first part of the 20th century particularly after 1913, scientists started realising in a much more comprehensive way than the decay of radioactive elements gives rise to ‘daughter atoms’. Two very straight forward rules were formulated -

  • If the nucleus of the radioactive element emits an alpha particle during the radioactive decay, the consequent production of the new element must be placed two periods to the left in the periodic table. (The atomic number decreases by 2)

  • If the radioelement emits Beta particles, the resulting elements must be placed one period to the right. (The atomic number increases by 1)

The element that was two periods to the right of Francium is Actinium and the element on the left-hand side of Francium is Radon. The problem was that Actinium was regarded as Beta transmitters and Radon was regarded as Alpha transmitters. 

If Actinium is a Beta transmitter, how can it produce an element that is two atomic numbers less than that of its own? And if Radon is an Alpha transmitter, how could it decay into Fr? This made scientists scratch their heads. The problem was solved, however, with the entry of the hero of this story. Read on…

Marguerite Perey: The Woman Who Discovered Francium

As said, Actinium was regarded as the parent of Francium. However, it was still not possible to prove the theory. Actinium was discovered by M.A. Debierne who worked alongside Marie Curie. Why we mentioned his name will be clear later on.

As the search for eka-Caesium was growing, a woman named Marguerite Perey started working as a lab assistant to help Marie Curie. Her primary task was to purify Actinium to get rid of the Uranium ores and other impurities. Even after the death of Marie Curie, Perey continued her work under Debierne and under the daughter of Marie Curie.

Interestingly enough, Perey never intentionally searched for the evidence of alpha radiation. She was interested in finding evidence that could back up the theory that Actinium emitted Beta radiation. 

While working with Actinium, Perey discovered that the element demonstrated an ascending amount of radioactivity till two hours from its obtaining. She also observed that the Beta ray being emitted from Ac was not as intense as she expected. She rightly thought that this Beta radiation could not be the radiation of thorium or uranium or other such daughter elements. Furthermore, she noticed that the radiation intensity changed with time, so this radiation could not have been the radiation of Ac. She also noticed that the Ac also emitted extremely mild Alpha radiation. All these revelations led her to believe that the Ac actually produced a new element and that new element, in turn, decayed into Radium by emitting Beta radiation.

This newly discovered element was named after France. Examining Francium is practically not possible because of its too unstable nature.

Discovery of Francium and Academic Snobbery 

The discovery of Francium was an extremely important event in the world of chemistry. The discovery of any new element, for that matter, is exciting. As Perey published a paper regarding the discovery, it was understood that she had enough chance to get a Doctorate because of this discovery. But Perey was just a lab technician and she was not allowed to submit her paper for a doctorate because she did not have the necessary degree in Chemistry. Only after she obtained a degree, she was allowed to submit the thesis.

This academic snobbery was rampant at that time and it is still present even today. Having a formal degree became more important than the revolutionary discovery.

Properties of Francium & Some Additional Information

Francium is a radioactive element

Its atomic number is 87

Francium is the last discovered natural element

Francium is extremely rare.

It is extremely unstable as well. It has a half-life of only 22 minutes

It is obtained through radioactive decay of Actinium.

Marguerite Perey discovered Francium.

Perey proposed that the element be named Catium. But due to the disapproval of the daughter of Marie Curie, it was named Francium.


There are many fake videos on Youtube that show how Francium explodes when it gets in contact with water. The videos are fake, but the theory is correct. Francium is an alkali metal and most alkali metals explode because of the Coulomb explosion theory. Francium will also produce extreme heat and radiation along with explosion if it gets in contact with water. Don’t think that with the discovery of elements like Francium or Organesson, the Periodic Table has become fully filled up. There are elements 119 and 120 or eka-Francium and eka-Radium respectively that are yet to be discovered! The story has just begun!

FAQ (Frequently Asked Questions)

1. What is Francium?

Ans. Francium is the last element discovered in nature. It is a radioactive element that is extremely reactive and unstable. It has the atomic number 87.

2. Who Discovered Francium?

Ans. Marguerite Perey discovered Francium in 1939. She was working with Actinium when she observed that Ac also emits mild Alpha radiation that results in the formation of Francium because of the radioactive decay.

3. Why is Francium Dangerous?

Ans. Francium is, first of all, a radioactive element. Any radioactive element is harmful to the human body. In fact, Marguerite Perey actually got cancer because of the prolonged exposure to Actinium (and therefore Francium). Secondly, Francium is an alkali metal and so it reacts violently with water resulting in an explosion.

4. Why was Francium Called eka-Caesium?

Ans. Before the discovery of any element, it is tentatively named by considering what element is above it and how many boxes above it in the Periodic Table. If a yet-to-be-discovered element has aluminium just one box above it, it will be named as eka-Aluminium. Similarly, if the yet to be discovered element has an already discovered element two or three boxes above it, it will be named as dvi or tri (respectively) followed by the name of the already discovered element. Before the discovery of Francium, there was Caesium above its designated box. So it was tentatively named as eka-Caesium.

5. What is eka-Francium?

Ans. Eka-Francium is the tentative name of the yet to be discovered element. It has been named as Ununennium. It is popularly known as element 119 based on its atomic number.

6. What are the Main Properties of Francium?

Ans. Here are the properties of Francium -

  • Fr is a radioactive element

  • It decays into radium

  • It produces Beta radiation.

  • It is the last natural element discovered to date.

  • Francium has an atomic number of 87.

  • It is an alkali metal.

  • Fr is highly unstable with a half-life of just 22 minutes.

  • Francium reacts violently with water