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an atom that has the same number of protons (or the same atomic number) as other atoms of the same element do but that has a different number of neutrons (and thus a different atomic mass)
can be used to represent an idea, object, or event that is too big, too small, too complex, or too dangerous to observe or test directly
a tabular arrangement of the chemical elements according to atomic number as based on the periodic law
a class of elements characterized by physical properties that include shininess, malleability, ductility, and conductivity
the ease and speed with which an element combines, or reacts, with other elements and compounds
a machine that moves atomic nuclei at higher and higher speeds until they crash into one another, sometimes forming heavier elements
one of the elements of Group 18 of the periodic table (helium, neon, argon, krypton, xenon, and radon); are unreactive
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