10. Playing with a Full Deck:
       The Periodic Table
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       Group IIA: The Alkaline Earths

Magnesium's light weight makes it useful in the aircraft industry, but the other metals in Group IIA have little application. The chief industrial use of Sr and Ba is to produce brilliant red and green flames for signal flares and fireworks. Barium sulfate, , being very dense to x-rays and at the same time relatively harmless and not assimilated by the body, is useful for contrast in medical x rays of the stomach and intestinal tract.

Calcium and magnesium are twice as prevalent in living organisms as are sodium and potassium, but not primarily as soluble ions. Calcium phosphate is the main component of bones and teeth in vertebrates, and calcium carbonate is the material of shells. and ions are found in many enzymes, and surrounded by a delocalized aromatic ring (a porphyrin ring) is the light-trapping unit in chlorophyll.

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