Patterns in the Periodic Table

What you'll learn

How the Periodic Table is arranged by proton number, how outer electrons relate to charge and reactivity, and the trends across Group 1 and Group 17.

• The Periodic Table is arranged by increasing proton number
• The period number equals the number of occupied electron shells
• The group number relates to the number of outer (valence) electrons
• Elements in the same group share similar chemical properties
• The number of outer electrons predicts ionic charge
• Metallic character decreases and non-metallic character increases across a period
• Group 1, the alkali metals, become more reactive down the group
• Group 17, the halogens, become less reactive down the group