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alpha particles

a particle with two protons and two neutrons with a 2+ charge

alpha radiation

radiation that is made up of alpha particles


the smallest particle of an element that retains all the properties of that element

atomic mass

the weighted average mass of the isotopes of that element

atomic mass unit

one twelfth the mass of a carbon- 12 atom

atomic number

the number of protons in an atom

beta particles

a high-speed electron with a 1- charge that is emitted during radioactive decay

beta radiation

radiation made up of beta particles

cathode ray

a ray of radiation that originates from the cathode and travels to the anode of a cathode ray tube

Dalton's atomic theory

a theory proposed by John Dalton in 1808, based on numerous scientific experiments that marked the beginning of the development of modern atomic theory


a negatively charged, fast-moving particle with an extremely small mass

gamma ray

high-energy radiation that has no electrical charge and no mass, it is not deflected by electric or magnetic fields, usually accompanies, alpha and beta radiation


atoms of the same element with the same number of protons but different numbers of neutrons

mass number

the number after an element's name representing the sum of its protons and neutrons


a neutral subatomic particle in an atom's nucleus that has a mass nearly equal to that a person

nuclear equation

a type of equation that shows atomic number and mass number of the particles involve

nuclear reaction

a reaction that involves a change in the nucleus of an atom


the extremely small, positively charged, dense center of an atom that contains protons


a subatomic particle in an atom's nucleus that has a positive charge of 1+


the rays and particles (alpha, beta, gamma) that are emitted by radioactive materials

radioactive decay

a spontaneous process in which unstable nucleus lose energy by emitting radiation


the process in which some substances spontaneously emit radiation


the SI unit used to measure the amount of a substance (atom)

molar mass

the mass in grams of one mole of any pure substance

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