| A | B |
|---|
| periodic table of elements | a table that organizes all the elements in order according to their properties |
| group | a column in the periodic table containing elements with similar properties |
| period | a horizontal row in the periodic table |
| atomic number | the number of protons in the nucleus of an atom of a particular element |
| atomic mass | the approximate number of protons and neutrons in an atom |
| proton | a positively charged particle of an atom in the nucleus of an atom |
| neutron | a part of an atom found in the nucleus; has no charge (neutral) |
| electron | a negatively charged particle of an atom with an extremely small mass; travels around the nucleus |
| *category / family | a group of elements that have similar chemical properties and that react similarly with other elements, e.g. the alkali metals, semi-metals |
| *shell | average distance away from a nucleus at which electrons can travel |
| *valence electron | an electron in an outer shell that can form chemical bonds with other atoms |
| *Bohr model (of an atom) | model that depicts an atom showing the number of protons and neutrons in the nucleus and the number of electrons in their shells |
