I wrote about this topic a few years ago, and thought I'd update it. Many chemists find themselves looking at a periodic table and wondering "How many of these things have I personally handled?" My list is up to nearly 45 elements (there are a couple that I've got to think about, one-off catalyst reactions from twenty-two years ago and the like). And there are at least 29 that I hope to never use at all, since they're radioactive and I'm generally not in the mood for that. So what does that leave me?
Well, I've never used beryllium, although it's not that I'm tapping my foot waiting for any. It's pretty toxic stuff, for the most part, and there are hardly any organic chemistry reactions that get near it. That means that I can't even think what I might use it for, and I could easily go my whole career without seeing any.
The next lowest molecule weight element I haven't messed with (excluding unreactive neon, which you at least get to see in its excited state) is probably scandium. That whole first column of transition metals is pretty useless for organic chemists, to be honest (Yttrium? Lanthanum?), and I've never seen any reactions that leapt out at me as things I had to try. No, if the answer is scandium, it must have been a pretty odd question.
Next up, I haven't used either of the G twins, gallium and germanium. They're not too well studied compared to their family members above and below: aluminum and even indium are more widely used than gallium, and silicon and tin show up in organic labs a million times more often than germanium. But with those relatives, you'd have to think that there's something interesting that can be done with these, so it depends on whether anyone finds out what that might be during the rest of my chemistry career.
And right next to these is arsenic, which I've also managed to avoid. It's famously poisonous, although it's really not worse than a lot of other things that get used much more often. But again, there's not a lot of compelling chemistry to be done with the stuff, not that I know of, anyway, and there are always those unfortunate nomenclature problems to be dealt with, especially if you have a British accent.
Krypton I've never had a use for, and I'd have to rate the chances as very low indeed. In the next row, I've handled strontium chloride, but only to make red-colored flames for a school demonstration show. I have yet to touch yttrium, as mentioned above, and I've managed to miss zirconium so far as well. There are actually a number of organometallic reactions that use that one, so it's at least a real possibility. Niobium I have yet to encounter, and at the rate it's used, I probably never will. Cadmium's another toxic beast - there are some old reactions that use organocadmiums, but I can't think when I saw a modern reference that used any of them, and I don't see this one in my future, either. Antimony I might use if I never need some horrible superacid. Tellurium, well. . .there would have to be a pretty good reason, given its reeking, nose-wrinkling sulfur and selenium relatives, but someone might yet come up with one. Can't rule that one out, unfortunately.
Now we're getting into the heavy metals, and a lot of gaps start to appear. Has anyone in an organic chemistry lab ever used hafnium or tantalum? Didn't think so. The best candidate for "something I could use, but haven't" in this bunch is osmium. The tetroxide is a very useful reagent that I just haven't had the need for. It wouldn't surprise me if that's the next addition to my list. I've no desire whatsoever to use thallium. It's part of a short run of nasties that you hit right after the jewelry metals - you have your platinum, then gold, and you think you're in the high-rent district, and suddenly it's mercury, thallium, and lead right in a row. Reminds me of the way towns were stuck next to each other in New Jersey.
And as far as the lanthanides, well, I've used cerium as a TLC stain, and once I used samarium iodide - which, true to its reputation, didn't work. None of the others have I touched, and unless I need some funky NMR shift reagent, which fewer and fewer people do these days, I don't see it happening. There are a lot of funny rare earths down there, but little reason for an organic chemist to go digging around among them.
Weirdest element I actually have handled? Xenon would have to be the winner - I've used the difluoride, and yes, that was the recourse of a desperate chemist. But it did work to turn a silyl enol ether into an alpha-fluoro ketone, so I can't say anything bad about it, other than its rather penetrating smell, which I probably should have taken more care not to experience. . .