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 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 below.
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.
