The space inside of all atoms expands, but it's to such a tiny degree that the forces of nature are far far more powerful and everything acts as it should. If space between an electron and proton expands a tiny tiny bit, it's less than the random motion of the electron anyway, that's why atoms don't fly apart due to expansion and it's the same for larger objects too. If the space inside the Earth expands by a billionth of a micrometer, gravity will keep everything in place. The expansion of space is minuscule, it presents itself only over massive distances. Here is a thought experiment you can do. Imagine a meter stick in your hand. Now imagine a magic force that caused it to expand 5%. It's now 1.05 meters long, a significant amount, but look at each millimeter mark by itself. It's 1.05mm now, not really that big of a deal. Now extrapolate, if the universe expands by light years as a whole, the amount we'd notice it within the tiny little speck that's planet Earth is next to nothing. Everything moves orders of magnitudes faster than the expansion of space except for at the most massive scales.