While many metals appear silver or grey, gold stands out with its warm, rich colour. But have you ever wondered why gold is yellow when most other metals are not?
Gold’s yellow colour comes down to the size and speed of its electrons. Gold atoms are incredibly heavy, with many protons in their nucleus. This makes their electrons orbit very close to the speed of light. At such high speeds, gold’s electrons experience relativistic effects — a phenomenon predicted by Einstein’s theory of relativity.
Here’s what happens in simple terms:
Relativistic Shrinking of Orbitals: The fast-moving electrons in gold behave as if they are heavier, pulling them closer to the nucleus and changing how they absorb and reflect light.
Energy Levels Shift: This shift lowers the energy required for gold to absorb light in the blue and violet part of the spectrum.
Since gold absorbs blue and violet light, the light it reflects back to our eyes is missing those cooler tones. What remains is a combination of yellow and red wavelengths, which creates gold’s signature yellowish hue.
Other metals, like silver, also have free-moving electrons, but they don't experience the same relativistic effects as gold because their atoms are smaller and lighter. As a result, silver reflects light more evenly across the spectrum, maintaining a neutral silver appearance.
Gold’s unique colour is just one of its many special traits. Thanks to its electron configuration, gold is highly resistant to tarnishing and corrosion, which contributes to its enduring appeal. Additionally, its malleability, conductivity, and rarity make it a favourite material for jewellery, electronics, and even space technology.
