| A | B |
|---|
| Atom | the smallest unit of an element and keeps its properties. |
| Electron | A particle that has a negative charge. |
| Nucleus | The atoms center or central region made up of protons and neutrons. |
| Electron Cloud | A region around the nucleus of an atom where electrons are likely to be found. |
| Proton | A particle that has a positive charge found in the nucleus of an atom. |
| Atomic Mass Unit | A unit of mass that describes the mass of an atom or molecule. |
| Neutron | a particle that has no charge and found in the nucleus of an atom. |
| Atomic Number | The number of protons in the nucleus of an atom and the atomic number is the same for all atoms of an element. |
| Isotope | An atom that has the same number of protons (same atomic number) as other atoms of the same element but has a different number of neutrons having a different atomic mass. |
| Mass Number | The sum of the numbers of protons and neutrons in the nucleus of an atom. |
| Atomic Mass | The mass of an atom expressed in atomic mass units. |
| Period | Describes something that occurs or repeats at regular intervals. |
| Periodic Law | Repeating chemical and physical properties of elements change periodically with the atomic numbers of the elements. |
| Period | Horizontal rows of elements in the periodic table. |
| Group | Vertical columns of elements in the periodic tablewhere elements share chemical properties. |
| Alkali metals | One of the Group 1 elements of the periodic table. |
| Alkaline-earth metal | One of the elements of Group 2 of the periodic table. |
| Halogen | One of the elements of Group 17 of the periodic table where they combine with most metals to form salts. |
| Noble Gas | One of the elements of Group 18 of the periodic table and are unreactive. |
