average mass of an atom of an element; its unit of measure is the atomic mass unit (u)

number of protons in the nucleus of each atom of a given element; is the top number in the periodic table

a substance produced when elements combine and whose properties are different from each of the elements in it

invisible, negatively charged particle located in a cloud like formation that surrounds the nucleus of an atom

natural or synthetic material that cannot be broken down into simpler materials by ordinary means; has unique properties and is generally classified as a metal, metalloid, or nonmetal

two or more atoms of the same element that have different numbers of neutrons in their nuclei

states that matter is not created or destroyed but only changes form

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

anything that takes up space and has mass

element that is malleable, ductile, a good conductor of electricity, and generally has a shiny or metallic luster

element that has characteristics of both metals and nonmetals and is a solid at room temperature

a combination of compounds and elements that has not formed a new substance and whose proportions can be changed without changing the mixture's identity

an uncharged particle located in the nucleus of an atom

elements that are usually gases or brittle solids and poor conductors of electricity and heat; are the basis of the chemicals life

positively charged, central part of an atom

positively charged particle located in the nucleus of an atom and that is counted to identify the atomic number

matter with a fixed composition whose identity can be changed by chemical processes but not by ordinary physical processes