It's possible you saw them in boldface in a specific context, but it's not a standard convention. Here are some reasons why you might have seen them in boldface:
* Emphasis: Someone might use boldface to emphasize a particular molecule in a text, similar to how we might boldface a word to highlight it.
* Technical Notation: In some specialized scientific publications or software, boldface might be used to indicate a particular type of molecule or its properties. However, this would be specific to the context and wouldn't be a general rule.
* Typographical Error: It's possible the boldface was a simple mistake.
To clarify, could you please provide more context about where you saw molecules in boldface? Knowing the source of the information would help me understand why they were written that way.
