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the smallest particle of an element that retains it identity in a chemical reaction

Atomic mass

a weighted average mass of the atoms in a naturally occurring sample of the element

Atomic mass unit

one twelfth of the mass of a carbon-12 atom

Atomic number

the number of protons in the nucleus of an atom of that element

Cathode ray

a stream of electrons produced at the negative electrode of a tube containing a gas at low pressure

Dalton's atomic theory

the first theory to relate chemical changes to events at the atomic level


a negatively charged subatomic particle


a vertical column of elements in the periodic table


atoms of the same element that have the same atomic number but different atomic masses due to different number of neutrons

Mass number

the total number of protons and neutrons in the nucleus of an atom


a subatomic particle with no charge and a mass of 1 amu; found in the nucleus of an atom


the tiny, dense central portion of an atom, composed of protons and neutrons


a horizontal row of elements in the periodic table

Periodic table

an arrangement of elements in which the elements are separated into groups based on a set of repeating properties


a positively charged subatomic particle found in the nucleus of atom

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