Recognize the significance of important members of groups 1a and 2a: sodium, potassium, magnesium, and calcium.

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The group 1a elements are called the alkali metals. Sodium and potassium are the two most common and most important members of this family.  They are both soft, silvery metals in their pure elemental forms.  But they are also highly reactive, especially with water.  As a result, they are only found in nature as chemical compounds with other elements, particularly oxides and halogens.  They both readily lose an electron to form singly charged cations.  They are both important biologically as major sources of electrolytes for the human body.  Both ions form concentration gradients in the body that help drive various chemical reactions.  Sodium in particular is important to help regulate osmotic water pressure and blood pressure.

The group 2a elements are called the alkaline earth metals.  Calcium and magnesium are two important members of this family.  They are also both metals in elemental form but they readily form doubly charged cations.  They are most commonly found in nature as minerals in the Earth's crust.  Both of these ions are also biologically important.  Magnesium is often important for enzyme activity and calcium is important for bone strength.

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