These numbers actually vary between atom to atom.
The sum of masses of protons, neutrons and electrons.
Protons and neutrons are the particles found in the nucleus of an atom. Protons have a positive charge, neutrons have no charge, and both are much heavier than electrons.
Protons and neutrons account for almost all the mass of an atom. Electrons have much less mass compared to protons and neutrons.
No actually, the neutrons and the protons of an atom are relatively the same in mass. Electrons have the smallest mass in an atom, and are not even considered when we look at the mas sof an atom.
The mass of an atom is determined by the sum of the masses of its protons, neutrons, and electrons. The protons and neutrons are located in the nucleus and contribute most of the mass, while the electrons, which have much less mass, orbit the nucleus. The mass of an atom is typically measured in atomic mass units (amu).
(The constituent particles of an atom are the electron, the proton and the neutron; all three are fermions. However, the hydrogen-1 atom has no neutrons and the hydron ion has no electrons.) WIkipedia
Protons and neutrons are subatomic particles that are responsible for most of an atom's mass. Protons have a positive charge, neutrons are neutral, and both are found in the nucleus of an atom. Electrons, which have a much smaller mass, orbit around the nucleus.
Electrons take up the least amount of space compared to protons and neutrons. Protons and neutrons are much larger in size compared to electrons and make up the majority of an atom's volume due to their mass.
An atom does have mass. The mass of an atom is primarily concentrated in its nucleus, which is made up of protons and neutrons. Electrons, which orbit the nucleus, have much less mass compared to protons and neutrons.
The electron, the proton and the neutron are the "building blocks" of the atom. Protons have a positive electrical charge (p+), and neutrons which have about the same mass, are electrically neutral, or have no electrical charged (n0). Electrons, which are much less massive than protons - only about 1/1836th as heavy - have a negative electrical charge (e-). All atoms are made of protons, neutrons and electrons, though most hydrogen (1H1) has just the proton in its nucleus and a lone electron in orbit.
Because they are much smaller than an atom
An atom's mass is concentrated in its nucleus, which is located in the center of the atom. Protons and neutrons within the nucleus are responsible for its mass; the electrons, which are located outside of the nucleus, don't contribute to the mass of the atom.