By Ron B. Davis Jr., Georgetown University
In the periodic table, group 2 elements have a lot in common with group 1 elements. However, group 2 elements have two valence electrons. As a result, group 2 is less reactive than group 1 and has a stronger metallic bond and a higher melting point. We call group 2 ‘alkaline’ because calcium, strontium, and barium—the first elements discovered in this group—form a metal hydroxide when they react with water.
Why Group 2 Elements Tend to Oxidize
The group 2 elements’ tendency to oxidize is so strong that the metals of group 2 were all first detected in their oxide forms: beryl is beryllium oxide, magnesia is magnesium oxide, lime is calcium oxide, strontian is strontium oxide, and baryta was an old name for barium compounds with oxygen or sulfur.
On the other hand, group 2 are called alkaline ‘earth’ metals because their oxides are less reactive than group 1. They have very low water solubilities and cannot normally be burned in air.
As the table predicts, each alkaline earth metal’s s2 electron configuration means that they tend to form a plus two ion, combining in a one-to-one ratio with oxygen. It was this property that landed them in group 2 of Mendeleev’s table, long before their atomic structure was uncovered.
Also, much like their group 1 neighbors, each element’s oxide or hydroxide and can be electrolyzed to obtain pure elemental metals—a technique that allowed Humphry Davy in the first decade of the 1800s to go on his famous tear of isolating new elements, including four of the alkaline earth metals.
This article comes directly from content in the video series Understanding the Periodic Table. Watch it now, on Wondrium.
Discovery of Magnesium and Calcium
Magnesium and calcium were the first alkaline earth metals to be discovered. This is in part because their similarities lead to magnesium and calcium commonly accumulating together in nature.
There is evidence that as far back as 4,000 years ago, ancient Mesopotamians used a very special substance that could be obtained by subjecting limestone to extreme heat in special kilns in a process called ‘calcining’’ By the 1600s and 1700s, this process became commonplace in the western hemisphere as a means of obtaining mortar for brick construction.
Natural limestone itself is made of a mixture of calcium and magnesium carbonates, and heating these substances drives off carbon dioxide gas, leaving behind a combination of metal oxides of both metals, known then as quicklime.
Surprising Features of Group 2 Elements
The alkaline earth metals from group 2 all tend to form insoluble oxide compounds that react with water or acids to form bases. Just as we saw with sodium and potassium for the alkali metals, the row 3 and row 4 representatives from this group—magnesium and calcium—are by far the most abundant of their group. Their high concentrations in our environment have made them readily available to participate in the evolution of biological chemistry as well.
The second column of the periodic table also has a few surprises. Beryllium’s universal abundance is shockingly low mostly because of its low nuclear binding energy, but its lithophilic characteristics have concentrated it in our Earth’s crust, making it available, and a valuable, material as a native metal because of its low density and its strength.
On the other hand, its unusually strong bonds to oxygen—more akin to those made by its diagonal neighbor aluminum—make it difficult to access in a bioavailable form. This has left the human body with no way to manage beryllium if it finds a way inside us.
Strontium and Radium
Strontium’s position just below calcium on the table accurately predicts that it can substitute for calcium in the body, making its radioactive isotopes particularly dangerous when they are released into our environment. We saw how barium’s name, literally meaning ‘heavy’, accurately describes the properties of some of its compounds, but falls short of describing its properties as a pure element.
And the final element of the group is radium. Radium definitely lives up to its name, as its ionizing radiation led to both its most famous and infamous application—production of luminescent paints that were wildly popular, but proved so dangerous to work with that their use precipitated a new era in labor force protection law. Although every element is unique in its own way, the s-block elements shared a great deal in common with one another.
Common Questions about Group 2 Elements
Group 1 and group 2 elements have much in common. Still, since the group 2 elements have two valence electrons, they are less reactive to some extent, form stronger metallic bonds, have higher melting points, and their oxides are less reactive than group 1. These elements also hardly solve in water and can not be burned in air.
These two elements were the very first alkaline earth metals to be discovered. They are also the most abundant group 2 elements. Their abundance and availability have led to their inclusion in the development of biological chemistry.
Beryllium has a low universal abundance. This feature of this group 2 element of the periodic table is due to its low nuclear binding energy. However, due to its lithophilic properties, it is concentrated in the earth’s crust and is a valuable native metal because it is strong and dense.
