Alkaline Earth Metal
Definition
The group 2 metals: reactive, but calmer than the alkali metals. Calcium in your bones and magnesium in chlorophyll are members.
Technical definition
Alkaline earth metals are the group 2 elements (Be, Mg, Ca, Sr, Ba, Ra) with two valence electrons in an ns^2 configuration. They are harder and less reactive than alkali metals, commonly form +2 ions, and their oxides produce alkaline solutions.
Example
Magnesium burns with a brilliant white flame, and calcium carbonate, from this family's chemistry, makes up limestone and seashells.
Common confusion
Despite the name, these are true metals. Earth is an old alchemist word for their oxides, which were once thought to be elements.