protons plus neutrons
To determine the number of protons, look at the atomic number. The number of electrons is also the atomic number.To find the number of neutrons subtract the atomic number from the Atomic Mass number.
To determine the number of neutrons in an atom, subtract the atomic number (number of protons) from the atomic mass number (rounded mass of the atom). Neutrons are particles found in the nucleus of an atom and carry no charge.
The characteristic of an atom that is not used to determine the number of neutrons is its atomic number. The atomic number indicates the number of protons in an atom, while the number of neutrons is derived from the difference between the atomic mass (which is the total number of protons and neutrons) and the atomic number. Therefore, only the atomic mass and the atomic number are needed to calculate the number of neutrons.
Atomic mass minus atomic number. This is rather simplified but the atomic mass of an element is the total of all the protons, neutrons, and electrons in an atom. Each proton and neutron has an atomic mass of approximately 1 AMU (atomic mass units) while an electron has an atomic mass of about 0.0005 AMU. So, you don't need to worry about the electrons. The atomic number of an element is simply the number of protons in the atom. So, atomic mass (number of protons and neutrons) minus atomic number (number of protons) equals number of neutrons in an atom.
Atomic mass and atomic number are two different things. Atomic mass is the mass of an atom compared to that of hydrogen. The atomic number is the atom's position in the periodic table. It's also the number of protons it has.
Number of Neutrons = Mass number - Atomic Number
Atomic Mass: protons AND neutrons atomic number: just protons
Proton + Nuetron = Atomic Mass
no --- atomic number
The numbers of protons and of electrons in an atom are both the same as the atomic number, and the difference between the mass number and the atomic number is the number of neutrons in the atom.
If you mean "how does one determine an atoms atomic mass?", then the answer would be to find a periodic table of elements where the whole numbers indicate atomic number and the other indicating atomic mass. Atomic number is generally described as the number of protons in a naturally occurring atom of a given element, and the atomic mass is the number of protons + number of neutrons in an atom.
It is impossible to determine the number of neutrons from the mass number and atomic mass, since the two are essentially same value. However, with the atomic number and the mass number, one can calculate the number of neutrons by subtracting the atomic number from the mass number.