Can atoms be of different sizes?

To expand on what Fabrice and Kyle have already answered, it's also possible for atoms of the same element to be “different sizes,” if we're talking about mass. Isotopes are variant forms of an element which have a different number of neutrons. read more

PS : If you are unaware that different atoms have different sizes, you need to learn much, much more physics before you can meaningfully speculate about things like cosmogenesis. Be prepared to take a lot of time doing this. read more

The simple answer is of course they can. Each element of the periodic table has an atomic size of its own. The hydrogen atom has 1 proton, no neutrons and a single electron; the iron atom has 26 protons, 30 neutrons and 26 electrons so it is larger. read more