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# 6.10: Alkaline Earth Metals

Sparklers like those people use on holidays make festive additions to many celebrations. You may use them yourself. But watch out if you do because their flames are really hot! The bright white flames are produced when magnesium burns. Magnesium is a light-weight metal that burns at a very high temperature. Other uses of magnesium include flash photography, flares, and fireworks. Magnesium is a metal in group 2 of the periodic table, which you will read about in this concept.

## The Second Group

Barium $$\left( \ce{Ba} \right)$$ is one of six elements in group 2 of the periodic table, which is shown below. Elements in this group are called alkaline Earth metals. These metals are silver or gray in color. They are relatively soft and low in density, although not as soft and lightweight as alkali metals.

Figure 6.10.1: Period 2 of the periodic table.

## Reactivity of Alkaline Earth Metals

All alkaline Earth metals have similar properties because they all have two valence electrons. They readily give up their two valence electrons to achieve a full outer energy level, which is the most stable arrangement of electrons. As a result, they are very reactive, although not quite as reactive as the alkali metals in group 1. For example, alkaline Earth metals will react with cold water, but not explosively as alkali metals do. Because of their reactivity, alkaline Earth metals never exist as pure substances in nature. Instead, they are always found combined with other elements.

The reactivity of alkaline Earth metals increases from the top to the bottom of the group. That's because the atoms get bigger from the top to the bottom, so the valence electrons are farther from the nucleus. When valence electrons are farther from the nucleus, they are attracted less strongly by the nucleus and more easily removed from the atom. This makes the atom more reactive.

## Examples of Alkaline Earth Metals

For a better understanding of alkaline Earth metals, let's take a closer look at two of them: calcium $$\left( \ce{Ca} \right)$$ and strontium $$\left( \ce{Sr} \right)$$. 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 in the figure below.

Figure 6.10.2: All these foods and drinks are rich in calcium.

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 the figure below, the compound strontium chloride reduces tooth sensitivity.

Figure 6.10.3: Strontium chloride, a compound found in some toothpastes, 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.

## Explore More

At the following URL, observe how four different alkaline Earth metals react with water. After you watch the video, answer the questions below:

1. Observe the reactions in the video, and then rank the alkaline Earth metals from most to least reactive with water.

2. What explains the differences in reactivity?

3. Predict the reactivity of beryllium with water. Where would it fit in your ranking?

4. What substances are produced in each reaction that you observed in the video?

## Contributors

• CK-12 Foundation by Sharon Bewick, Richard Parsons, Therese Forsythe, Shonna Robinson, and Jean Dupon.