Francium, a rare and highly radioactive element, marks a significant milestone in the history of scientific discovery. Its existence was predicted decades before its actual discovery. As element 87 on the periodic table, francium was an elusive substance, existing in minute quantities and decaying rapidly. Its discovery highlighted the persistent efforts required to complete the periodic table.
Marguerite Perey and the Discovery
The discovery of francium is credited to Marguerite Perey, a French physicist. She began her career as a personal assistant to Marie Curie at the Radium Institute in Paris in 1929. Perey’s expertise was in isolating and purifying radioactive elements, with a focus on actinium. This foundational work provided her with the understanding necessary for her discovery.
In 1935, Perey encountered a research paper reporting unusual beta particle emissions from actinium-227. She hypothesized these emissions originated from an unknown decay product of actinium, not actinium itself. To investigate, Perey meticulously purified samples of actinium-227.
Her precise measurements revealed that approximately one percent of actinium’s radioactivity stemmed from alpha particle emission, which involves the expulsion of two protons and two neutrons from an atom’s nucleus. Since actinium has 89 protons, the loss of two protons indicated a new element with 87 protons. Perey observed this new product exhibited chemical properties of an alkali metal, closely resembling cesium, and would co-precipitate with cesium salts. This behavior confirmed her identification of element 87, completing a long-sought gap in the periodic table.
Perey’s initial suggestion for the element’s name, “catium,” was not adopted. She then proposed “francium,” honoring her home country, France. The International Union of Pure and Applied Chemistry (IUPAC) officially adopted the name in 1949. Francium holds the distinction of being the last naturally occurring element discovered.
The Unique Characteristics of Francium
Francium is one of the rarest naturally occurring elements on Earth, with estimates suggesting that less than 30 grams exist in the entire crust at any given time. Trace amounts are continuously formed in uranium ores as a decay product of actinium-227.
This element is also the most unstable of the first 103 elements on the periodic table. Its most stable isotope, francium-223, has a half-life of 22 minutes, meaning half of any given sample decays into other elements within that timeframe. Francium isotopes typically undergo either alpha or beta decay.
Positioned in Group 1 of the periodic table, francium is a heavy alkali metal, residing directly below cesium. It shares chemical similarities with other alkali metals, such as lithium, sodium, potassium, rubidium, and cesium. Due to its inherent instability and extreme rarity, francium has no practical commercial applications. Its study is primarily confined to scientific research, serving as a subject for experiments in spectroscopy to understand atomic structure and the behavior of heavy elements.