| A | B |
|---|
| atom | the building block of all substances. |
| nucleus | the center of the atom. It contains nearly all of the mass. |
| atomic mass | approximately equals the sum of the protons and neutrons. |
| Protons | sub-atomic particles that have a positive electrical charge (+1) and a mass of about 1. They determine the type of atom and are found in the nucleus . |
| atomic number | equals the number of protons in the nucleus of an atom. |
| Neutrons | sub-atomic particles with no electrical charge (they are "neutral") and a mass of 1. They help to keep the nucleus together. |
| Electrons | sub-atomic particles with a negative electrical charge ( -1); they have very little mass and they are scattered outside of the nucleus. |
| ion | an atom or group of atoms that has an electrical charge due to gaining (-) or losing (+) electrons. |
| Isotopes | atoms of the same type (same number of protons) but with different mass, due to a different number of neutrons. |
| Radioactive decay | the release of alpha "waves" when an atomic nucleus breaks apart into lighter pieces. |
| isotope name | a hyphenated word specifying the type of atom and its atomic mass. |
| molecule | a chemical combination of two or more atoms. |
| formula unit | a single example of a group of ions that bind together because of electrical attraction. |
| element | a substance made up of only one type of atom. |
| compound | a substance formed of elements joined chemically. It contains either identical molecules or identical formula units. |
| pure substance | an element or a compound. |
| mixture | made of elements and/or compounds mixed together. It can be separated by physical methods. |
