Sorry for my late reply, didn’t realise someone wrote a comment. You’ve probably understood by now what I meant, but still, here are the answers:

Q1: By keeping order from lightest to heaviest atoms, you are able to more quickly organise your atoms in the symmetry. The reason behind this is that the game is giving a random atom within a short range. By being organised, you’ll be able to quickly arrange symmetric atoms (of course, you’d have to break the lowest-to-highest chain, but that’s ok when building such a symmetry).

Q2: After combining the atoms, you’d get N (7), O (8), Na (11), Ne (10). This is the best result you can achieve while combining the atoms, so that you stay closest to rule #1. Na (11) and Ne (10) are very close to each other, which gives you yet another possibility for future combination.

Thanks for the hint, I’ll see what I can do.