One or two trillion in just the observable universe, which may only be a tiny fraction of the total universe. I read in one of Brian Greene’s books that if inflation theory is correct, the universe must be at least 10^20 times the radius of the visible horizon. And since volume increases with the cube of the radius, that’s how many galaxies? Answer: unimaginable.
And the Milky Way galaxy is estimated to have 100 billion to 400 billion stars. Just think how many stars and planets are in the universe!
That’s a lot of hydrogen atoms!