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: The modern [[Periodic Table]] was arranged by a scientist called [[Mendeleev]]. Others had tried to arrange all the [[element]]s before, but [[Mendeleev]] was the first to arrange by both [[Atomic Number]] and [[Chemical Properties of Elements|chemical properties]].
: The columns of the [[Periodic Table]] are called [[Group]]s.
: The rows of the [[Periodic Table]] are called [[Period (Chemistry)|Period]]s.
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====Trends within groups====
The [[Chemical Property|chemical properties]] of [[element]]s within a [[group] are similar. However, the [[reactivity]] within a [[group]] changes as you move up or down the [[Period (Chemistry)|period]]s.
*[[Group 1]]: The [[Alkali Metal]]s all react strongly with water. The [[reactivity]] increases as you go down the [[group]].
*[[Group 2]]: The [[Alkali Earth Metal]]s all react strongly with steam and acids. The [[reactivity]] increases as you go down the [[group]].