Normally, we think of relativity as part of physics in general, not chemistry. So first, let's look at a chemical property of metal. This video does a great job of explaining why metals reflect light:
But one thing the video doesn't go into is why gold and copper don't reflect all of the visible spectrum. It's actually pretty interesting.
If gold did reflect blue light, it would violate causality and do something weird like push the electrons through time!
Instead, the fact that gold is constrained by relativity is referred to Relativistic Effects in chemistry. In fact, chemists are using computer models to find properties of elements with or without relativity. It's useful because certain properties appear only in certain configurations.
For example, mercury does not appear to have Relativistic Effects in its gas phase, but in its liquid phase, it allows the element to stay liquid at lower temperature, which is weird.
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