Platinum (Pt) and gold (Au) are highly valued precious metals used widely in jewelry and investment. Platinum is significantly denser than gold, meaning an identically sized piece of platinum will weigh more than gold. This difference is rooted in the fundamental properties of the elements and affects practical applications.
Defining Density: The True Measure of “Heaviness”
When comparing materials, the correct scientific measure is density: the mass contained within a specific volume. Density is distinct from weight, which depends on the object’s size, and is expressed in grams per cubic centimeter (g/cm³). For pure materials, platinum has a density of approximately 21.45 g/cm³.
Gold, while exceptionally dense, has a value of about 19.3 g/cm³ in its pure form. This difference means that a cubic inch of platinum will have roughly 11% more mass than a cubic inch of gold. Density explains why platinum is considered heavier than gold when comparing equal volumes of each metal.
The Atomic Reason for the Difference
The explanation for platinum’s greater density lies in how its atoms are structured and organized. Platinum atoms have a slightly lower atomic weight than gold atoms (195.084 u vs. 196.96657 u, respectively). Despite the individual gold atom being marginally heavier, platinum is denser because of its atomic packing. Both metals share the same face-centered cubic crystal structure, but platinum atoms are arranged more compactly.
Platinum’s atoms pack into a crystal lattice with a shorter unit cell length than gold, meaning the distance between atoms is smaller. This tighter arrangement allows more platinum atoms to fit into the same volume of space. The greater number of platinum atoms packed into a given volume outweighs the slightly heavier mass of an individual gold atom, yielding a higher overall density.
Real-World Effects of Density
The density difference has tangible effects, particularly when comparing jewelry made from the two metals. A platinum ring will feel noticeably heavier on the finger than a gold ring of the exact same design and dimensions. This substantial heft is a characteristic many people associate with platinum jewelry.
The final product’s density is also affected by purity standards, as both metals are typically alloyed for practical use. Platinum jewelry is often 95% pure (950 parts per thousand), while gold purity, measured in karats, is frequently lower, such as 18-karat gold (75% pure). Platinum’s high density is also useful in industrial applications where stability is required, such as in specialized laboratory equipment and catalytic converters.