For me, ‘attraction’ is simply being physically attracted to them; a fluttering in the chest, so to speak, enjoying the eye candy…
When it changes to ‘love’ though, I found my thoughts to be more on wanting to take care of them, seeing them smile, being happy when they are happy. It goes beyond the superficial and the physical. I suppose the best way I can describe it is it makes my soul sing.
I think the Ancient Greeks, with their words for different kinds of love, were more on point with these sorts of things.
Chemistry is something different again. Lust and Love are all well and good, but you need more than that to make a relationship work. You need mental maturity on the part of both parties, the willingness to move beyond and work through problems, and something of a similar life trajectory in order to make love last.