| A | B |
|---|
| atom | the smallest particle of an element that still retains the properties of the element |
| nucleus | positively charged center of an atom that contains protons and neutrons and is surrounded by a cloud of electrons |
| proton | particle, composed of quarks, inside the nucleus of an atom that has a charge of 1+ |
| neutron | neutral particle, composed of quarks, inside the nucleus of an atom |
| electron | particles surrounding the center of an atom that have a charge of 1- |
| quark | particles of matter that make up protons and neutrons |
| electron cloud | area around the nucleus of an atom where the atom's electrons are most likely to be found |
| atomic number | number of protons in an atom's nucleus |
| mass number | sum of the number of protons and neutrons in an atom's nucleus |
| isotope | atoms of the same element that have different numbers of neutrons |
| average atomic mass | weighted-average mass of the mixture of an element's isotopes |
| periodic table | organized list of all known elements that are arranged by increasing atomic number and by changes in chemical and physical properties |
| group | vertical column in the periodic table |
| electron dot diagram | uses the symbol for an element and dots representing the number of electrons in the element's outer energy level |
| period | horizontal row in the periodic table |
