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the smallest particle into which an element can be divided and still be the same substance


a unifying explanation for a broad range of hypotheses and observations that have been supported by testing


the negatively charged particles found in all atoms


a representation of an object or system


the tiny, extremely dense, positively charged region in the center of an atom

electron clouds

the regions inside an atom where electrons are likely to be found


the positively charged particles of the nucleus

atomic mass unit

the SI unit used to express the masses of particles in atoms


the particles of the nucleus that have no charge

atomic number

the number of protons in the nucleus of an atom


atoms that have the same number of protons but have different numbers of neutrons

mass number

the sum of the protons and neutrons in an atom

atomic mass

the weighted average of the masses of all the naturally occurring isotopes of an element

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