Osmium (Os): A Noble Metal in Character, but with Beastly Properties and a Heart of Gold

Periodic Table, Source: Wiki commons

In this miniseries, we will be showcasing a number of different rarely mentioned elements, both in industry and day-to-day from the periodic table. Shining light on their true nature and amazing properties.

In this week’s instalment, a rarely mentioned noble metal Osmium (Os). Number 76 on the periodic table, only 3 doors next to everyone’s favourite precious metal, Gold (Au). Funnily enough, Os is considered as a platinum group metal. Additionally it is much rarer than gold, about 1000 times. Being the 2nd least abundant stable metal on planet earth (1st being Iridium, Osmium’s neighbour). Discovered relatively recently compared to other metals, in 1803 by Smithson Tennant. The name Osmium comes from the Greek word ‘osme’ meaning odour. Nowadays, the production of this metal comes as a by-product of Nickel (Ni) and Copper (Cu) mining. From mines in South Africa, Russia and Canada.

Interestingly, being about 1000 times rarer than Gold. Osmium is still not as expensive as Gold, being around $400 USD per ounce compared $1,300 USD per ounce. This is partly because it has very few commercial applications.

Properties

Have you ever realised how heavy and dense metals can be? Osmium is on another level. Os is the densest element on the periodic table, at about 22.6 g cm-3. Meaning that 1 litre of Osmium metal would weight around 22.6 kg!!! Additionally, Os has a beautiful slight blue-grey colour. Unlike other metals and platinum group metals (Platinum, Iridium, Ruthenium, Rhodium and Palladium), which are silvery.

You may have heard people biting on pure Gold to determine it purity, but you would not want to do that with Osmium. It has a beastly hardness, like quartz (SiO2) which makes up sand (7.0 on the Mohs hardness scale). Therefore, used where hardness and durability is required. Such as fountain pens, electrical contacts and hardcore ball bearings.

Osmium Crystal, Source: Wiki commons

Chemically, Osmium metal (i.e. its pure form) is relatively boring. However its compounds, have wide applications. From use in the field of cell biology, organic chemistry (as a catalysts) and even used in space, on space mirrors due to its extreme reflectivity. Moreover, Osmium is rarely used by its self. It is Normally alloyed with other metals. Used in applications where materials need to be hard, durable and have an extreme temperature range (Osmium has the 4th highest melting point at 3033 oC).

Chemistry

Its siblings, Iron (Fe) and Ruthenium (Ru) being part of the same row, have very similar chemistry. One of the most interesting chemical properties of Osmium, is a solid compound called, Osmium Tetroxide (OsO4). Imagine if iron rust could evaporate just like water and be more poisonous than Arsenic or Cyanide, and smell like chlorine. This is what a form of rust of Osmium can do. For inorganic compounds, it is very rare for it to smell, normally only organic chemicals do. This dangerous compound, can causes serious lung, skin or eye damage (causing blindness) and lead to death! Therefore, the pure form of osmium is rarely used because of the fear of the oxidation of Osmium to OsO4. So, for that reason, the production of Osmium is only around 500kg yearly. 5000 times less than gold. However, OsO4 is useful for the production of alcohols and staining of biological sample and even in some clinical uses.

Osmium Tetroxide Label, Source: Wiki commons

Still, Osmium compounds has shown great promise for use as possible anti-cancer drugs recently. Which currently are dominated by platinum based drugs (such as cisplatin). Also, Os little brother Ruthenium has shown great promise as well. So due to Ru and Os’s very similar chemistry. The field of osmium based cancer drugs has showcased a possible new candidate for the development of new medicines.

However, because of its high price, low production rate and safety concerns. Osmium is very rarely explored in chemical research, unfortunately.

Like many other chemists, we only handle a handful of different elements in our research. Therefore, I will unlikely never explore the chemistry surrounding Osmium, a true valiant element. ☹

Remember to check back next week, where we will be showcasing another rarely mentioned element.