| A | B |
|---|
| nucleus | center of atom, contains protons and neutrons |
| proton | positive subatomic particle, located in nucleus |
| neutron | neutral subatomic particle, located in nucleus |
| electron | negative subatomic particle, outside of nucleus |
| energy level | possible energies an electron may have |
| orbital | region where there is a high probability of finding electrons |
| valence electrons | electron in the outermost energy level |
| period | horizontal row of elements |
| group | vertical column of elements |
| ionization | process of adding or removing electrons from an atom or group of atoms |
| ion | atom or group of atoms that has lost or gained electrons |
| cation | ion with positive charge |
| anion | ion with negative charge |
| atomic number | number of protons or electrons |
| mass number | number of protons and neutrons in the nucleus |
| isotopes | same element, different number of neutrons |
| atomic mass unit (amu) | equal to one-twelfth of the mass of a carbon-12 atom |
| average atomic mass | weighted average of the masses of all naturally occurring isotopes of an element |
| metals | shiny, good conductors |
| nonmetals | dull, brittle, poor conductors |
| semiconductors | elements are intermediate conductors, properties of metals and nonmetals |
| alkali metals | high reactive metals in group 1 |
| alkaline-earth metals | reactive metals in group 2 |
| transition metals | groups 3-12 |
| halogens | highly reactive nonmetals in group 17 |
| noble gases | unreactive gases in group 18 |
| mole | SI base unit that describes the amount of a substance |
| Avogadro's constant | number of particles in 1 mole; 6.02 X 10 23 |
| molar mass | the mass in grams of 1 mole of a substance |
| conversion factor | ratio equal to one that expresses the same quantity in two different ways |
| periodic law | properties of elements tend to change in a regular pattern due to increasing atomic number |
