There are a number of issues with your suggestion, ranging from basic grammar to the more factual appropriateness.
The more grammatical issues:
- dividintur isn't Latin -- the form you are looking for would be dividuntur.
- the demonstrative pronoun ejus (its) should be the relative pronoun cujus (whose, or "of which").
If cujus particulae calore dividuntur is supposed to translate "thermonuclear," I see a number of issues:
- dividere as a verb for nuclear fission seems actually fine, except that findere, findo, fisi, fissum already sort of owns the spot, I suppose.
- For "atoms," I would honestly just say atomi (classically attested! although obviously not quite in the modern sense), or elementa.
- A thermonuclear reaction is a fusion reaction only powered by the temperature or pressure of the matter. So the description is completely off.
If findere seems appropriate for fission, fundere could easily appear to be the obvious choice for fusion, but no: it simply means "pour, shed," and confundere is right (I suppose scientists could not very well have reported to their superiors that they had achieved "nuclear confusion").
So you could say: ... cujus elementa suo calore ipsa impulsa in unum confunduntur.
Or, you know, you could just say thermonuclearis. Unfortunately that's a Greek-Latin mix, which some people dislike.
The Vatican's own, notoriously purist Lexicon Recentis Latinitatis seems to call an H-Bomb pyrobolus hydrogenicus (at least it's all Greek). So for your napalm, how about Pyroglia hydrogenica? (Feminine, i.e. it's Sancta pyroglia, etc.; with such words, you can also use Greek declension endings if you want, i.e. illius pyroglias etc., please see Wiktionary for what they all are.) This means, roughly, "hydrogen fire glue." That is, of course, assuming your napalm is based on fusing hydrogen atoms ...