Would you also say that you cannot "train" intelligence?

I would agree that generally, purely acquiring knowledge does not increase intelligence. But I would also argue that intelligence (ie your raw "processing power") can be trained, a bit like a muscle. And acquiring and processing new knowledge is one of the main ways we train that "muscle".

There's lots of examples where your definition of intelligence (intelligence == raw processing power) either doesn't make sense, or is so narrow that it becomes a meaningless concept. Let's consider feral children (ie humans growing up among animals with no human contact). Apparently they are unable or have trouble learning a human language. There's a theory that there's a critical period after which we are unable to learn certain things. Wouldn't the "ability to learn a language" be considered intelligence? Would you therefore consider a young child more intelligent than any adult?

And to answer your question, whether learning about atoms makes you more intelligent: Yes, probably. It will create some kind of connections in your brain that didn't exist before. It's a piece of knowledge that can be drawn upon for all of your thinking and it's a piece of knowledge that most humans would not figure out on their own. By basically any sensible definition of intelligence, yes it does improve your intelligence.