We need to be more specific when talking about how heavy an element is. There are two possible ways to define the “heaviest” elements – based on their density or atomic mass.
The heaviest element in terms of density can be defined as mass per unit volume, which is usually measured in grams per cubic centimeter or kilograms per cubic meter.
The densest naturally occurring element on Earth is Osmium. This shiny substance has a density of 22.59 g/cm3, slightly more than that of Iridium.
Another way to look at heaviness is in terms of atomic weight, the average mass of atoms of an element. The standard unit of atomic mass is one-twelfth of the mass of a single carbon-12 atom.
This is a fundamental concept in chemistry because most chemical reactions occur according to the simple numerical relationships among atoms. Below, we have listed seven heaviest elements found on Earth according to their atomic masses.
Note: We haven’t mentioned elements whose properties are unknown or not yet confirmed, such as moscovium, flerovium, nihonium, and meitnerium.
Atomic mass: 267
Rutherfordium (Rf) was the first super-heavy element to be discovered [in 1964]. It is highly radioactive, and its most stable isotope 267Rf has a half-life of about 78 minutes.
Rutherfordium is an artificial element created in the laboratory by bombarding Californium-249 with a Carbon-12 nuclei. A total of 16 isotopes have been reported with atomic masses between 253 and 270. Most of these decay rapidly via spontaneous fission pathways.
The element is expected to be solid under normal conditions and presumed to have chemical properties similar to hafnium. It has only been created in minuscule amounts and used for scientific research only.
Image credit: ChemistryLearner
Atomic mass: 268
Dubnium (Db) is a radioactive element, first synthesized in 1968 at the Joint Nuclear Research Institute, Russia. It has seven recognized isotopes, out of which the most stable one is 268Db with a half-life of 32 hours.
Dubnium can be produced by bombarding either californium-249 with nitrogen or americium-243 with neon. A limited examination of Dubnium chemistry has confirmed that the element behaves more like niobium instead of tantalum, breaking periodic trends.
Since the element is neither found free in nature nor created in bulk quantities at the laboratory, it has no applications other than scientific research.
Atomic mass: 269
Seaborgium (Sg) was first synthesized in 1974, at the Lawrence Berkley Lab, California. The research team bombarded californium-249 with oxygen-18 nuclei to produce seaborgium-263.
It’s a radioactive element whose most stable isotope (269Sg) has a half-life of about 14 minutes. Only a few seaborgium atoms have ever been produced, and its use is solely for scientific research.
The little research that has been carried out on this synthetic chemical element indicates that seaborgium is dense, heavy metal under normal conditions.
In 2014, Japanese researchers established a chemical bond between a carbon atom and seaborgium for the first time, opening new doors for analyzing the effects of Einstein’s relativity on the structure of the periodic table.
Atomic mass: 270
Bohrium (Bh) is an artificially produced radioactive element named after a famous physicist Niels Bohr. It is synthesized by bombarding bismuth with chromium ions.
Since it decays very quickly through the emission of alpha-particles (270Bh has a half-life of 61 seconds), it very difficult to study the element.
Bohrium is not found in nature, and only a few atoms have been produced to date. It will perhaps never be isolated in observable quantities.
Atomic mass: 270
Discovered by German physicists in 1984, Hassium (Hs) is one of the heaviest and densest elements in the periodic table. All nine isotopes of the element have very short half-lives: the most stable one (270Hs) has a half-life of 10 seconds.
So far, only a few hassium atoms have been produced. Thus, its properties are yet to be known. Although the exact melting point, boiling point, and density are not confirmed, the element is believed to be solid at room temperature.
This radioactive, transition metal might react with other elements [of its group] if produced in bulk quantities. As of now, it has no commercial use other than scientific research.
Atomic mass: 294
Tennessine (Ts) is the second-heaviest known element discovered by a Russian-American collaboration in 2010. It is a radioactive, artificially produced element. Although its classification is unknown, it is expected to be solid.
Tennessine was produced by a fusion reaction of calcium-48 with berkelium-249. In all experiments performed so far, its atoms have lasted tens and hundreds of milliseconds.
The use of tennessine is restricted to research purposes because of its minuscule production. Its most stable isotope (294Ts) has a half-life of about 80 milliseconds, which decays through alpha decay.
Atomic mass: 294
First synthesized in 2002, Oganesson (Og) is the heaviest element in the periodic table. This highly radioactive element is a member of the noble gas group. Surprisingly, this is the first noble gas that is chemically reactive.
Since 2005, only six atoms of Oganesson have been identified. It exhibits very unusual physical and chemical properties, most of which are not well understood yet.
Since Oganesson is very unstable (with a half-life of approximately 0.89 milliseconds) and doesn’t occur naturally, there is almost no reason to consider its health hazards.
Heaviest Naturally Occurring Element: Uranium
Uranium glass glowing under ultraviolet light | Credit: Wikimedia Commons
Atomic mass: 238.0289
For more than six decades, Uranium (U) has been used as an abundant source of concentrated energy. It is the heaviest element found in Earth’s crust, being 500 times more common than gold and 40 times more common than silver.
Although uranium is a radioactive element, its rate of decay is much slower than other elements associated with radioactivity. Its most naturally occurring form (uranium-238 ) has a half-life of about 4.5 billion years.
Uranium is mostly used as a nuclear fuel to produce electricity in nuclear power stations. One kilogram of uranium-235 can generate nearly 80 terajoules of energy, which equivalent to the energy generated by 3,000 tons of coal.
It’s an extremely toxic element: ingestion of hexavalent uranium compounds can result in immune system damage and birth defects.