Bohrium: An Introduction
Bohrium (Bh) is a synthetic chemical element with atomic number 107. It is classified as a superheavy element, meaning its atomic nucleus contains a very large number of protons. Bohrium does not occur naturally on Earth, including in India or elsewhere. It is exclusively produced in specialized nuclear physics laboratories through particle accelerators, where lighter atomic nuclei are fused together. Due to its synthetic nature and extremely short half-life, only a few atoms of Bohrium have ever been created. This makes studying its properties exceptionally challenging.
Chemical Reactivity
The chemical reactivity of Bohrium is largely theoretical and based on predictions from its position in Group 7 (VIIB) of the periodic table, directly below Rhenium (Re) and Technetium (Tc).
Reactivity with Water and Air
Due to the vanishingly small quantities produced (a few atoms at a time) and its extremely short half-lives (e.g., the most stable isotope, $^{270}$Bh, has a half-life of about 61 seconds), it is impossible to observe Bohrium’s reaction with water or air in a macroscopic sense. However, based on its expected metallic character, analogous to Rhenium, Bohrium is predicted to be relatively unreactive with both water and air under standard conditions. Rhenium, for instance, is a noble metal that resists corrosion and does not readily react with oxygen or water. It is hypothesized that Bohrium would exhibit similar inertness, though this remains an unconfirmed theoretical prediction.
Expected Oxidation States
Similar to its lighter congener Rhenium, Bohrium is expected to exhibit a maximum oxidation state of +7. Studies aiming to probe its chemistry have focused on this prediction, along with potentially stable lower oxidation states like +5, +4, and +3.
Key Characteristics
Toxicity
Bohrium is inherently toxic, not due to conventional chemical toxicity, but primarily due to its intense radioactivity. All superheavy elements are extremely radioactive and would pose severe radiological hazards if produced in quantities large enough to interact with biological systems. Even trace amounts would emit highly energetic radiation.
Radioactivity
Bohrium is an extremely radioactive element. All its known isotopes are unstable and decay rapidly, primarily through alpha decay. This high radioactivity is the defining characteristic of Bohrium and all superheavy elements, necessitating stringent safety protocols in their handling and study within laboratories.
Flammability
As a metal, Bohrium is not expected to be flammable in the typical sense of combustion (burning in air or oxygen). Its primary hazard and characteristic are related to its radioactivity, not its flammability.
Investigating Bohrium’s Chemistry
There is no “famous” chemical reaction involving Bohrium in the same way there are common reactions for everyday elements. This is because macroscopic quantities do not exist, and chemical studies are limited to experiments involving single atoms.
The most notable chemical investigations involve gas-phase thermochromatography experiments. In these studies, individual atoms of Bohrium are produced and then reacted with carefully chosen gaseous reagents, often containing halogens (like chlorine or bromine) and oxygen. For instance, atoms of Bohrium have been reacted with a mixture of oxygen and hydrochloric acid or hydrobromic acid. The goal is to form volatile compounds, such as oxychlorides (e.g., BhO$_3$Cl) or oxybromides (e.g., BhO$_3$Br). The adsorption properties and volatility of these compounds are then studied by observing where they condense along a temperature gradient in a chromatography column. This allows scientists to infer the chemical properties of Bohrium, such as its most stable oxidation states and bonding characteristics, by comparing its behaviour to that of its lighter homologs, Technetium and Rhenium. These highly specialized experiments are critical for understanding the fundamental chemistry of the heaviest elements.