Gold (Au) and platinum (Pt) are two highly sought-after precious metals, known for their unique properties and distinct aesthetic appeal. They are often compared regarding which is truly heavier. Platinum is significantly denser than gold, making it the heavier material when comparing equal volumes. This difference in mass results from their fundamental physical structures and has practical implications for how each metal is used.
The Direct Comparison of Density
Density is a fundamental physical property that describes the amount of mass contained within a specific volume. It is the ratio of an object’s mass to its volume, which determines how “heavy” a material feels for its size. Gold is already a highly dense element, possessing a density of approximately \(19.32 \text{ g/cm}^3\). This high value explains why even small gold objects feel substantial in the hand.
Platinum, however, surpasses gold in this measurement, with a density of about \(21.45 \text{ g/cm}^3\). This means that platinum is roughly 11% denser than gold. If a jeweler were to craft two identical rings, the platinum ring would weigh noticeably more than the gold one. This density difference is a measurable trait that is often used to authenticate precious metals.
The Atomic Reason for the Weight Difference
The reason for platinum’s greater density lies in the arrangement of its atoms at the microscopic level. Gold has an atomic number of 79, meaning each atom contains 79 protons, while platinum has an atomic number of 78. An individual gold atom is slightly heavier than a platinum atom, with atomic masses of \(196.97 \text{ g/mol}\) and \(195.08 \text{ g/mol}\), respectively. However, this small mass difference does not explain the bulk density distinction.
Both metals share the same face-centered cubic crystal structure. The determining factor is the spacing between the atoms within this structure. Platinum atoms are more tightly packed than gold atoms, resulting in a smaller unit cell size. Platinum’s interatomic distance is shorter, allowing its atoms to occupy less space per unit of volume. This efficient packing arrangement makes bulk platinum significantly denser than gold.
Practical Differences Beyond Density
Gold and platinum exhibit several distinct physical characteristics that influence their practical uses beyond density. Platinum boasts a much higher melting point than gold, requiring temperatures of approximately \(1768^\circ \text{C}\) to melt, compared to gold’s \(1064^\circ \text{C}\). This elevated thermal resistance makes platinum substantially more difficult for jewelers and refiners to work with.
Platinum is also a harder metal than pure gold, contributing to its superior durability and resistance to wear. While gold is prized for its high malleability, platinum is often preferred in applications demanding strength, such as settings for valuable gemstones. Furthermore, platinum is found in much lower concentrations in the Earth’s crust, making it a rarer commodity than gold. This scarcity contributes to its high market value and prestige.