Alkaline earth metal

The alkaline earth metals are a family of six chemical elements.

You can find them in group 2 of the periodic table. This group includes beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). These elements are all shiny, silvery-white metals. They are also somewhat reactive at standard temperature and pressure. Most of these metals occur naturally in the environment. However, radium is unique because it only occurs through the decay chains of uranium and thorium. It is not considered a primordial element.

These metals share a specific atomic structure that dictates how they behave. Every element has electrons organized into shells around its center. The alkaline earth metals all have a full outer s orbital containing exactly two electrons. This configuration makes them very likely to lose those two electrons. When they lose these electrons, they form cations with a +2 charge. This process allows them to reach a more stable, filled electron shell configuration. This shared electronic pattern is why they are grouped together in the periodic table.

Each member of the group has distinct physical and chemical properties. They are generally soft metals with relatively low densities. They also have lower melting and boiling points compared to many other metals. Beryllium is a notable exception in many ways. It does not react with water or steam unless it is at very high temperatures. Its chemical bonds are covalent rather than ionic. Most other members, like calcium and strontium, react with water to produce hydrogen gas and strongly alkaline hydroxides.

Chemical reactions also reveal unique identities for each metal. For example, the alkaline earth metals react with halogens to form halides. Most of these are ionic crystalline compounds, but beryllium halides are covalent. These metals also react with oxygen to create oxides. You can identify different metals by the colors they produce in a flame test. Calcium produces a brick-red flame.

Strontium creates a crimson color. Barium can even produce an apple-green color.

History shows how our understanding of these elements evolved. Early chemists used the term "earth" for substances that were insoluble in water and resistant to heat. These substances were often metal oxides like lime or magnesia. In 1789, the chemist Antoine Lavoisier realized these earths were actually compounds, not elements. He suggested they might be metal oxides in his book, "Elements of Chemistry." In 1808, Humphry Davy proved this hypothesis. He used electrolysis, which uses electricity to separate substances, to obtain the actual metals from molten earths. This discovery led to the name "alkaline earth metals."

Stability and radioactivity vary greatly across the group. The first five metals have several stable isotopes. For instance, magnesium has three stable isotopes, while barium has six. Radium is different because all of its isotopes are highly radioactive. It is produced by the decay of heavier elements like uranium. Some isotopes, like strontium-90, are common products of uranium fission in nuclear reactors. Other isotopes, such as calcium-48 and barium-130, are extremely long-lived. They are so stable that they are considered primordial for practical purposes.

These elements have surprising connections to biology and medicine. Because they behave chemically like calcium, certain radioactive isotopes are known as "bone seekers." They move into the human skeleton and accumulate in the bone marrow. This can cause damage from ionizing radiation. However, doctors can use this trait for good in radiotherapy. They use specific radionuclides to target and treat cancerous growths in bone matter. This allows the treatment to hit the cancer while leaving much of the rest of the body unharmed.