| A | B |
|---|
| Albert Einstein | German physicist who proved the existence of atoms. |
| Atomic Mass Number | The total number of protons and neutrons in an atom's nucleus. |
| Atomic Nucleus | The center of an atom; it contains protons and neutrons. |
| Atomic Number | The number of protons in the nucleus of an atom. |
| Dmitri Mendeleev | Russian chemist who developed a periodic table of the chemical elements and predicted the discovery of several new elements (1834-1907). |
| Electron | A subatomic particle that has a negative charge and exists in a cloud formation around an atom's nucleus. |
| Element | A material that cannot be broken down into more fundamental parts. |
| Gasses | Molecules move freely around, they are not close together, changes shape easily and a solid can pass through it easily. |
| Half-Life | The time required for one-half of the atoms of a radioisotope to emit radiation and decay products. |
| Halogens | Contains nonmetals, 7 valence electrons in its outermost energy level. Very reactive. |
| Ion | An atom or group of atoms that has gained or lost one or more electrons, thus acquiring a charge. |
| Isotope | Atoms of the same element that differ in the number of neutrons they contain. |
| Metalloids | Elements that may accept or donate electrons readily and possess a mixture of metallic and nonmetallic properties. |
| Metals | Elements that are good conductors of electric current and heat. |
| Neutron | A subatomic particle of about the same mass as a proton but without an electric charge, present in all atomic nuclei except those of ordinary hydrogen. |
| Nobel Gasses | The least reactive family of elements in the periodic table, don't react or form bonds with other elements. |
| Periodic Table | A table that shows the elements, their atomic number, symbol, and average atomic mass; elements with similar chemical properties are grouped together. |
| Periodic Table Groups | Elements that exhibit similar chemical properties; arranged in columns on the periodic table. |
| Periodic Table Period | Elements in the same row on the periodic table (have the same number of energy levels). |
| Proton | A subatomic particle that has a positive charge and that is found in the nucleus of an atom. Mass = 1 amu |
| Radioactive Elements | Unstable elements that decay or break down into different elements. |
| Reactive Elements | Elements with unfilled valence shells. The atoms of these elements will react or they will chemically bond in order to fill the outer shell. |
| Transitional Metals | Metals located in groups 3-12, they have a moderate range of reactivity and a wide range of properties. |
