Here's why:

* The nucleus contains protons and neutrons. These particles are much heavier than electrons and carry a positive charge (protons) or no charge (neutrons).

* Electrons orbit the nucleus. They exist in a cloud-like region around the nucleus, called the electron cloud. These electrons are much lighter than protons and neutrons and carry a negative charge.

Think of it like this: Imagine the nucleus as a tiny, dense sun at the center of an atom. The electrons are like planets orbiting the sun, but they're not actually in a specific orbit, but rather in a region of space where they are most likely to be found.