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2.52: Alkaline Earth Metals

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Sparklers like the one this girl is holding 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 (Ba) is one of six elements in group 2 of the periodic table, which is shown in Figure 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. You can watch a brief video introduction to the alkaline Earth metals at this URL: http://www.youtube.com/watch?v=DFQPnHkQlZM .

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.

Q: Alkali metals have just one valence electron. Why are alkaline Earth metals less reactive than alkali metals?

A: It takes more energy to remove two valence electrons from an atom than one valence electron. This makes alkaline Earth metals with their two valence electrons less reactive than alkali metals with their one valence electron.

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 in Figure below .

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, 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.

Vocabulary

  • alkaline Earth metal : Metal in group 2 of the periodic table that has two valence electrons and is very reactive but less so than an alkali metal.

Practice

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

http://www.youtube.com/watch?v=B2ZPrg9IVEo (0:16)

  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?

Review

  1. What are alkaline Earth metals? What are their physical properties?
  2. Why are alkaline Earth metals very reactive?
  3. Compare and contrast the reactivity of beryllium (Be) and barium (Ba).

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Difficulty Level:

At Grade

Grades:

7 , 8

Date Created:

Oct 31, 2012

Last Modified:

Sep 05, 2014
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