Ah, my chemistry department taught me the other way around. I distinctly remember the phrase "methyl-ethyl" being thrown around a bit. Additionaly, we were taught to be more specific about isomers, hence me using butan-2-yl instead of isobutyl.

Then again, scientists often disagree strongly about things like this, so we could both be right. Also, there's a good chance this is just the A-Level specification being weird. I left my old textbook at my student flat, though, so I won't be able to check for a couple of weeks.

I could also be downright wrong myself.

As for the hydrogens, I had assumed they were not present, and that this lossane molecule is an ion with a charge of -50. This is borderline impossible to achieve in real life, of course.