answer:I don’t see why they would “have to”, since most chemists don’t work with all elements. On the other hand, just like readers memorized the alphabet and how to spell and define thousands of words during grammar school, I don’t see any reason that should prevent chemists from not only memorizing the elements (in order), but also knowing what groups and families they appear in, which ones have similar properties to each other, as well as isotopes of each. Familiarity sometimes breeds more familiarity.