| A | B |
|---|
| Atomic number | the number of protons in the nucleus of an atom; used to determine an element's position in the Periodic Table |
| Chemical property | a characteristic of a substance that describes how it combines with other substances to form new ones |
| Groups (families) | the vertical columns on the Periodic Table |
| Periods | the horizontal rows on the Periodic Table |
| Periodic Table | a conceptual model in which the elements are organized according to their properties; often displayed as a chart |
| Periodic trend | a regular variation of certain characteristics of elements to increase or decrease along a period (row) or group (column) of the Periodic Table of elements |
| Physical property | property of matter that can be observed without changing the composition or identity of the matter |
| Reactivity | tendency of a substance to undergo chemical changes in a system |
| Valence electrons | electron(s) located in outer energy level (electron shell) |
