Francium (Fr) is the heaviest alkali metal on the periodic table. It is a highly unstable, radioactive, and one of the rarest naturally occurring elements on Earth. The number of electrons Francium possesses is determined by its position on the periodic table and dictates its unique chemical behavior.
Determining the Total Electron Count
Francium has an atomic number of 87, which is the defining characteristic of the element. This number represents the precise count of protons within the nucleus. In a neutral Francium atom, the number of electrons orbiting the nucleus must exactly match the 87 protons to maintain a zero net electrical charge. Therefore, a neutral Francium atom contains exactly 87 electrons. This simple numerical relationship between protons and electrons in the neutral state is the basis for determining the electron count of every element.
Electron Arrangement and Valence Shells
The 87 electrons in Francium are arranged in a specific shell structure around the nucleus. Since Francium is located in the seventh period of the periodic table, its electrons occupy seven distinct principal energy levels, or shells. The distribution of electrons across these shells, moving outward from the nucleus, is 2, 8, 18, 32, 18, 8, and 1. The outermost, or seventh, shell contains only a single electron.
This solitary outermost electron is known as the valence electron, and it determines Francium’s chemical activity. Because the atom has only one valence electron, it readily gives up this electron to achieve a more stable configuration. This characteristic places Francium in Group 1, the alkali metals. The electron configuration is written as \([Rn] 7s^1\).
The Distinct Properties of Francium
Francium’s electron structure makes it theoretically the most chemically reactive of all the alkali metals. This extreme reactivity is related to its low ionization energy, which is the energy required to remove that single valence electron. Francium is also considered the least electronegative of all elements, meaning it has the lowest tendency to attract electrons.
Francium is intensely radioactive and extremely rare. The most stable isotope, Francium-223, has a half-life of only about 22 minutes. Because of this rapid decay, scientists estimate that less than 30 grams of Francium exist naturally in the Earth’s crust at any given moment. This instability means Francium has no commercial uses and is only studied in trace amounts or when artificially produced.