The number of neutrons is variable.
Subatomic particles are protons, neutrons and electrons.
The number of neutrons is different for isotopes.
Isotopes are atoms, not subatomic particles.
All the isotopes of chemical elements contain protons, neutrons and electrons.
Same number of protons; different number of neutrons. The number of electrons will also be the same, assuming a neutral atom.
An isotope is defined as: Each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element So basically, an isotope is from the same place (element) and has the same number of protons, but the number of electrons differ. So isotopes are not subatomic; the protons and electrons that make an isotope are subatomic.
mass #= # of protons + # of neutrons
These particles are electrons.
The subatomic particles that contribute most almost no weight to an atom are electrons at various energy levels. Isotopes of the same element differ from each other only by the number of neutrons.
The subatomic particle that makes atoms of different elements different from each other is the proton. This is given as the atomic number of the element on the periodic table.
All atoms of chemical elements contain protons, neutrons (excepting the isotope H-1)and electrons. The natural isotopes of bromine are 79Br and 81Br. For the list of all isotopes see the link below.
The atomic mass is the sum of the number of protons and the number of neutrons found in each atom of that element (electrons do not contribute). They are sometimes seen on periodic tables to have a decimal in the atomic number, this is for elements with more than one common isotope (an isotope of an element is the same number of protons but with a different number of neutrons), in which case an average of the common isotopes can be used.