The number of electrons
protons
Atomic number is same as the number of protons and number of electrons.
protons and electrons
The atomic number is the number of protons in the nucleus. The protons are positive particles, and so the number of them is matched by the number of electrons orbiting the nucleus. The organisation of the electrons determines how an element behaves when it reacts.
The proton
The "Atomic number" of an element corresponds to the number of only the protons in the nucleus of its atoms. Add to that the number of neutrons that are also in there, and you have the "Atomic weight".
They don't contain the same number of particles because some particles are more dense than others making one atom and another atom the same mass but not have the same number of particles.
protons is the same number as the atomic number always and protons plus the average number of neutrons makes up the atomic mass
The number of protons determines the element, and is the same as its atomic number.
They are called Isotopes
Atomic mass and molar mass are similar concepts but not the same. Atomic mass refers to the average mass of an atom of an element, while molar mass is the mass of one mole of a substance. The mass number of particles can be the same in certain cases, such as isotopes of the same element which have the same number of protons and different numbers of neutrons.
Protons are positively charged particles found in the nucleus of an atom. The number of protons in the nucleus determines the element's atomic number. Neutrons are neutral particles also found in the nucleus, and together with protons, they determine the atomic mass of the element.