| A | B |
|---|
| Nucleus | The very small center core of an atom. |
| Proton | Has a positive elective charge. |
| Neutron | Has no charge. |
| Electron | Has a negative elective charge. |
| Atomic number | The number of protons in the nucleus. |
| Isotope | Atoms with the same number of protons and a different number of neutrons. |
| Mass number | The sum of the protons and neutrons in the nucleus. |
| Model | May be a diagram, a mental picture, a mathematical statement, or an object that helps explain ideas about the natural world. |
| Atomic mass | The average mass of all the isotopes of that element. |
| Periodic table | A chart of the elements showing the repeating pattern of their properties. |
| Chemical symbol | A one or two letter representation of an element. |
| Period | The horizontal row of elements in the periodic table. |
| Group | Elements in the vertical column of the periodic table; also called family. |
