If you're seeing this message, it means we're having trouble loading external resources on our website.If you're behind a web filter, please make sure that the domains *.and *.are unblocked.In fact, the number of protons determines what atom we are looking at (e.g., all atoms with six protons are carbon atoms); the number of protons in an atom is called the atomic number.
Forms of the same atom that differ only in their number of neutrons are called isotopes.
Together, the number of protons and the number of neutrons determine an element’s mass number: mass number = protons neutrons.
In the middle is the letter symbol for the element (e.g., H).
Below is the relative atomic mass, as calculated for the isotopes found naturally on Earth.
It also shows up in popular culture: many superheroes’ origin stories involve radiation exposure, for instance—or, in the case of Spider-Man, a bite from a radioactive spider.
But what exactly does it mean for something to be radioactive? Radioactive atoms have unstable nuclei, and they will eventually release subatomic particles to become more stable, giving off energy—radiation—in the process.
If you want to calculate how many neutrons an atom has, you can simply subtract the number of protons, or atomic number, from the mass number.
A property closely related to an atom’s mass number is its atomic mass.
Often, elements come in both radioactive and nonradioactive versions that differ in the number of neutrons they contain.
These different versions of elements are called isotopes, and small quantities of radioactive isotopes often occur in nature.
Since an element’s isotopes have different atomic masses, scientists may also determine the relative atomic mass—sometimes called the atomic weight—for an element.