least - electron
most - the top quark
The least massive principle atomic particle is the electron. Neutrons and protons are much more massive and are about equal in mass. Of course, there are even smaller particles such as quarks which are less massive than even electrons.
Yes, a particle can be a single atom.
Protons and neutrons are found in the nucleus. While these are theoretically composed of quarks (conversely even more massive particles), quarks do not exist in a free state so are not "fundamental particles" by definition.
The 'rest mass' of the photon is zero ... but the photon is never at rest, and it has plenty of mass at the speed of light, at which it is always traveling. so that let's the photon out. Amongst particles that actually have rest mass, but not much of it, the neutrino probably has the least.
99.9% of an atom's mass is concentrated in the nucleus, with protons and neutrons having almost the same mass, with neutrons being slightly higher. So your question would be, 'What atom has the most protons and neutrons combined?' And that answer is Nobelium. Nobelium has 102 protons and 160 neutrons which makes it the most 'massive' atomic particle, even more so then Lawrencium which has 103 protons but only 159 neutrons. Of course, in a few months, we could have a new, more massive element.
electron
least - electron most - the top quark
The least massive principle atomic particle is the electron. Neutrons and protons are much more massive and are about equal in mass. Of course, there are even smaller particles such as quarks which are less massive than even electrons.
Which particle? The electron.
The three main subatomic particles are the proton, neutron, and electron. Of these three, the electron has the least amount of mass at about 0.0005 amu or atomic mass units.
the electron
an alpha particle is made of two protons and 2 neutrons. its basically the same as the nucleus of a helium atom
In the atom this particle is the electron. Generally in the particle physics: photons, gluons, neutrinos.
the electron
The element hydrogen is least massive as it has only one proton, one electron.
Neutrons are... very slightly... more massive than protons.
A proton is a subatomic particle found in the nucleus of an atom. It has a positive electrical charge and is roughly 1,836 times more massive than an electron. The number of protons in an atom determines its atomic number and chemical properties.