Imagine holding two metals, one so dense that a small piece feels surprisingly heavy, while the other is light enough to float on water. This remarkable contrast exists between osmium and lithium, two metals at opposite ends of the density scale.
Osmium is the densest naturally occurring element, with a density of about 22.59 g/cm³ — making it more than twice as dense as lead. Interestingly, it has been used in specialised applications, including high-quality pen nibs.
At the other end is lithium, the lightest metal, with a density of just 0.534 g/cm³. It is so light that it can float on water, although it reacts vigorously with it. One of the most important uses of lithium is in rechargeable batteries for mobile phones, laptops, digital cameras and electric vehicles. Lithium oxide is used in special glasses and glass ceramics. Lithium hydride is also used as a means of storing hydrogen for use as a fuel.
This remarkable difference shows how dramatically the physical properties of metals can vary and why each finds its own place in science, industry and technology.
