| Term | Definition |
|---|
| element | substance that cannot be broken down into simpler substances. |
| electrons | negatively charged particle that exists in an electron cloud formation around an atom's nucleus. |
| proton | positively charged particle in the nucleus of an atom. |
| neutron | electrically neutral particle that has the same mass as a proton and is found in an atom's nucleus. |
| electron cloud | region surrounding the nucleus of an atom, where electrons are most likely to be found. |
| atomic number | number of protons in the nucleus of an atom of a given element. |
| isotope | atoms of the same element that have different numbers of neutrons. |
| mass numbers | the sum of neutrons and protons in the nucleus of an atom. |
| radioactive decay | process in which some isotopes break down into other isotopes, releasing energy and particles from the nucleus |
| transmutation | the changing of one element into another through radioactive isotope to decay |
| half-life | time it takes for half the atoms of a radioactive isotope to decay. |
| period | third-longest division of geologic time; subdivided into epochs and characterized by the types of life that existed worldwide |
| group | family of elements in the periodic table that have similar phyiscal or chemical properties |
| metal | element that has luster, is malleable and ductive, and is a good conducter of heat and electricity |
| nonmetal | element that is usually a gas or brittle solid at room temperature and is a poor conductor of heat and eletricity |
| metalloid | element that shares some properties with metals and nonmetals. |
| representative element | elements in Group 1 and 2, and 13 through 18 in the periodic table that include metals,metalloids, and nonmetals |
| transition element | elements in Group 3 through 12 in the periodic table, all of which are metals |
| semiconductor | element that does not conduct elecricity as well as a metal but conducts it better than a nonmetal |
| catalyst | substance that speeds up a chemical reation but is not used up itself or permanently changed |
| synthetic elements | elements that do not occur naturally and are made in laboratories |
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