2.52. Alkaline Earth Metals http://www.ck12.org
Examples of Alkaline Earth Metals
For a better understanding of alkaline Earth metals, let’s take a closer look at two of them: calcium (Ca) and
strontium (Sr). Calcium is a soft, gray, nontoxic alkaline Earth metal. Although pure calcium doesn’t exist in nature,
calcium compounds are very common in Earth’s crust and in sea water. Calcium is also the most abundant metal
in the human body, occurring as calcium compounds such as calcium phosphate and calcium carbonate. These
calcium compounds are found in bones and make them hard and strong. The skeleton of the average adult contains
about a kilogram of calcium. Because calcium—like barium—absorbs x-rays, bones show up white in x-ray images.
Calcium is an important component of a healthy human diet. Good food sources of calcium are pictured inFigure
2.106.
FIGURE 2.106
Q:What health problems might result from a diet low in calcium?
A:Children who don’t get enough calcium while their bones are forming may develop a deficiency disease called
rickets, in which their bones are softer than normal and become bent and stunted. Adults who don’t get enough
calcium may develop a condition called osteoporosis, in which the bones lose calcium and become weak and brittle.
People with osteoporosis are at high risk of bone fractures.
Strontium is a silver-colored alkaline Earth metal that is even softer than calcium. Strontium compounds are quite
common and have a variety of uses—from fireworks to cement to toothpaste. In fireworks, strontium compounds
produce deep red explosions. In toothpaste, like the one pictured in theFigure2.107, the compound strontium
chloride reduces tooth sensitivity.
Summary
- Elements in group 2 of the periodic table are called alkaline Earth metals. They are silvery or gray in color.
They are also relatively soft and low in density. - Alkaline Earth metals are very reactive because they readily give up their two valence electrons to achieve a
full outer energy level, which is the most stable arrangement of electrons. Reactivity increases from the top to
the bottom of the group. - Examples of alkaline Earth metals include calcium, which is needed for strong bones, and strontium, which is
used for making cement and other products.