Periodic Table

• electron configuration: the arrangement of electrons in an atom's outer shell. (2,8,8)
• elements in group 0 (noble gases) are unreactive because they have full outer shells
• properties of noble gases: inert, monatomic, low boiling point, low density.
• halogens: 7 electrons in outer shell, gain 1 electron to have a full outer shell and form negative ions, reactivity decreases as you go down