| A | B |
|---|
| atom | The basic particle from which all elements are made. |
| electron | A negatively charged particle that is found outside the nucleus of the atom. |
| nucleus | The central core of the atom. |
| proton | A positively charged particle that is part of an atom's nucleus. |
| energy level | The specific amount of energy an electron has. |
| neutron | A small particle in the nucleus of the atom, with no electrical charge. |
| atomic number | The number of protons in the nucleus of an atom. |
| isotope | An atom with the same number of protons and a different number of neutrons from other atoms of the same element. |
| mass number | The number of protons and neutrons in the nucleus of an atom. |
| atomic mass | The average mass of all the isotopes of an element. |
| periodic table | A chart of the elements showing the repeating pattern of their properties. |
| period | A horizontal row of elements in the periodic table. |
| group | Elements in the same vertical column of the periodic table. |
| chemical symbol | A one- or two-letter representation of an element. |
