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the smallest particle of an element


tiny region in the center of the atom that has all of the atom's protons and neutrons


positively charged particles in the nucleus


negatively charged particles that orbit the nucleus


particles that have no charge found in the nucleus

energy level

determines the specific amount of energy that an electron has

atomic number

the number of protons in the nucleus of an atom


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

mass number

sum of the protons AND neutrons found in the nucleus of an atom

atomic mass

average mass of all of the isotopes of an element


horizontal row on the periodic table


a vertical column on the periodic table

chemical symbol

a one or two letter symbol used to designate each element


state of matter that consists of a gas-like mixture of free electrons and nuclei of atoms that have been stripped or electrons

nuclear fusion

process in which two atomic nuclei combine, forming a larger nucleus and releasing large amounts of energy


the ability to be stretched into wire


the ability of an object to transfer heat or electricity to another object


the ease and speed with which an element combines or reacts with other elements and compounds


when a metal combines with oxygen in the air to weaken the metal (rusting is a form of this)

alkali metals

group 1 elements

alkaline earth metals

group 2 elements

transition metals

the elements in groups 3 thru 12

particle accelerators

move atomic nuclei faster and faster until they have reached very high speeds


element that lacks the properties of a metal

diatomic molecule

consists of two atoms


the highly reactive group 17 elements

noble gases

the nonreactive group 18 elements


elements that have some properties of both metals and nonmetals


can conduct electricity under some conditions but not under other conditions

radioactive decay

the atomic nuclei of unstable isotopes release fast-moving particles and energy


spontaneous emission of radiation by an unstable atomic nucleus.

alpha particle

consists of 2 neutrons and 2 protons and is positively charged; same as a helium nucleus

beta particle

a fast moving electron given off by a nucleus during radioactive decay

gamma radiation

consists of high-energy waves similar to x-rays

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