"Gold is a chemical element."
Translation:Gold ist ein chemisches Element.
Because to say that "gold is a chemical element", in either English or German, is to speak about all gold generally and not about some specific gold. Adding the article makes it more specific (yes, sometimes German uses slightly different logic to decide when to use the article, but here it's the same).
Its chemisches to show the Neuter gender of Element, right? Because the ein is not clear