| A | B |
|---|
| Chemical symbol | A capital letter or a combination of a capital letter and a small letter that is used to represent an element |
| Periods | The horizontal rows of elements |
| Average atomic mass | An average of the masses of all the isotopes that occur in nature |
| Groups | Vertical columns of elements |
| Transition elements | Elements in the middle of the periodic table, periods 4 through 7 |
| Atomic number | The number of protons in an atom |
| Quarks | Makes up protons and nuetrons |
| Nucleus | The center of an atom where protons and nuetrons are located |
| Mass number | A total count of the neutrons and protons in an atom |
| Isotopes | Atoms of the same element but with different numbers of neutrons |
| Metals | Elements that are found on the left side of the periodic table |
| Metalloids | Elements that have both properties of metals and non-metals |
| Electrons | The particles that move about the nucleus and have a negative charge |
| Electron cloud | The region around the nucleus occupied by electrons |
| Periodic table | A chart that shows the classification of the elements |
