Trap One: Only the Protons Decide the Element
This is the big one. It is always the proton count — and only the proton count — that names the element. Not the electrons, not the neutrons, not the mass. People reach for “it's the number of electrons” or “it's how heavy it is”, and both are traps. You can mess with the neutrons and the electrons all day long; as long as the proton count stays at 6, it stays carbon. Change a single proton, though, and you've made a different element entirely.
Trap Two: Isotopes — Same Element, Different Neutrons
Here's a thing that surprises people: two atoms of the same element can have different numbers of neutrons. These are called isotopes. Carbon-12 has 6 protons and 6 neutrons; carbon-14 has 6 protons and 8 neutrons. Different mass numbers (12 versus 14), different weights — but both are still carbon, because both still have 6 protons. The neutrons changed the mass, not the identity. Drag the neutron count in the toy and watch the mass number move while the element name stays put.
Trap Three: Ions — Same Element, but Now Charged
An atom can gain or lose electrons, and when it does, the positives and negatives stop balancing. Lose an electron and there's now one more proton than electron, so the atom is overall positive. Gain an electron and it tips negative. An atom with a charge like this is called an ion. But — and this is the catch — it's still the same element, because you only moved electrons and the proton count never budged. A sodium atom that loses an electron is still sodium; it's just a sodium ion now, carrying a positive charge.
And the Quiet One: the Atom Is Mostly Empty Space
It's worth saying again because it's so easy to forget. The nucleus is fantastically tiny compared with the whole atom — the electrons roam a region thousands of times wider than the nucleus itself, and between them is essentially nothing. So when you picture an atom, don't picture a packed marble. Picture a speck in the middle of a vast empty hall, with a few even tinier specks drifting around the edges. Almost all of “solid” matter is, honestly, empty.