I would say proton and electron are the two most important subatomic particles in an atom. The number of protons inside a nucleus must equal to the number of electrons outside of the nucleus. This number determines all the chemical properties of the atom, which governs the behaviors of all matters in our world.

The nucleus is in the center of the atom, and it has protons and neutrons. The electrons are outside the nucleus, taking up lots of space. I don't think any of them is the boss; they all work together.

Atoms do not have bosses. Atoms are composed of three subatomic particles: protons, neutrons, and electrons. Protons and neutrons are themselves composed of quarks. The number of protons determines the element of the atom, the number of neutrons determines the isotope, and the number of electrons determines the ionization state.

I would say the proton is the “boss,” since the number of protons determines the atomic number and therefore the chemical identity of the atom.

For example if the nucleus has 6 protons, then it is always a Carbon atom and can only be a Carbon atom, but if the nucleus has 7 protons, it is always Nitrogen. In nuclear chemistry, protons can be kicked out the of nucleus and this causes the atomic number to change, causing one atom to transform into another, giving off radiation. For example, in a nuclear reaction called alpha decay, the nucleus emits an alpha particle (atomic number 2, which is a Helium nucleus), thus transforming the original atom into another element with atomic number reduced by 2.

Adding or removing electrons, only changes the charge of the atom, making it ionic or neutral, but does not change the atom’s atomic number or identity. For example, Nitrogen with 7 electrons is neutral, but Nitrogen with 8 electrons would still be Nitrogen but with a net negative charge of -1. Changing the number of neutrons also does not change the chemical identity of the atom, but only changes its mass.