Alkaline Earth Metals
Alkaline Earth Metals are metals that are found in Group II of the periodic table. Six elements such as Beryllium, Magnesium, Calcium, Strontium, Barium and Radium are placed in this group. These metals show resemblance to alkali metals (Group I in the periodic table), which is why they are placed besides them in the periodic table.
The chemical elements found in Group II of the periodic table are called alkaline earth metals. The six chemical elements that constitute the periodic table are beryllium, magnesium, calcium, strontium, barium and radium. These elements have +2 oxidation number, making them highly reactive and thus are not found free in nature but as carbonates or sulfates. They share several similar characteristics as the alkali metals of Group I in the periodic table, and thus are placed just next to alkali metals. The most striking resemblance is their high reactivity.
Alkaline earth metals have two electrons in their valence shell of their atoms, and their general configuration is written as [Noble gas]ns2.
Element Symbol Atomic Number Electronic Configuration
Beryllium Be 4 [He]2s2
Magnesium Mg 12 [Ne]3s2
Calcium Ca 20 [Ar]4s2
Strontium Sr 38 [Kr]5s2
Barium Ba 56 [Xe]6s2
Radium Ra 88 [Rn]7s2
Atomic and Ionic Radii
Compared to the atomic and ionic radii of alkali metals, the radii of alkaline earth metals is smaller due to the higher nuclear charge which causes the electrons to be attracted to the nucleus, thereby resulting in reduction of atomic and ionic size. As we move from Be to Ra in the group, it is observed that the atomic radius increases due to the increase in the atomic number, number of shells and screening effect.
Alkali earth metals are not as reactive as alkali metals, however, they are more reactive than other elements in the periodic table. They react with water to form metal hydroxide and hydrogen gas. Due to the presence of two electrons in their valence shells, they are seen to form cations with a charge of 2. Since these elements have high reactivity, they are found in the form of compounds such as sulfates and carbonates instead of the free form. Magnesium in its pure form is combustible in nature and burns with an intense white light when brought in contact with air (as it combines with air to form magnesium oxide). The other elements of this group also form oxides when reacted with oxygen.
Boiling and Melting Points
The temperature at which a solid element turns into liquid state and liquid element into vapor state is called melting and boiling points respectively. In case of alkaline metals, as the atomic number increases, the boiling point and melting point are seen to decrease in the group. However, in case of alkaline earth metals no regular pattern or trend is seen. Beryllium has the highest melting and boiling point in the group and Magnesium has the lowest. However, since the atomic radii of alkaline earth metals are smaller than those of alkali metals, the boiling and melting points of Group II is higher than Group I elements. Thus, we can use the boiling and melting points test to differentiate between Group I and II elements.
Since Group II elements have a larger radii, they have higher ionization energies as compared to Group I elements. As we move down Group II, the atomic number and size increases, as the number of shells increase and the magnitude of screening effect is also seen to be higher. However, this causes the ionization energy to decrease down the group.
Metallic Character and Density
Alkaline earth metals are electro-positive in nature, which increases down the group. However, Group II elements are not as electro-positive as Group I elements due to their higher ionization energies. These elements are harder and denser as compared to alkali metals. This is because the smaller atomic size causes the electrons to be packed more closely, thereby forming strong metallic bonds. This is why these metals are harder and denser than alkali metals.
Physical and Chemical Behavior
Group II elements are mostly good conductors of electricity since they are highly metallic in nature. They are shiny and generally white or silvery in color. They are soft metals but harder and denser than alkali metals. When freshly cut, these metals have a gray-white appearance, which is seen to tarnish as soon as it is exposed to air. Chemically, these elements are strong reducing agents as they have two valence electrons in their valence shell, which they readily give away during chemical bond formation. The free elements are soluble in liquid ammonia, imparting a metallic, copper-like appearance. These solutions are very helpful in various chemical processes.
Of the six elements in Group II, calcium is the most widely available element and not only ranks fifth among the elements found in the Earth’s crust, but also ranks fifth among the elements in the human body. Magnesium ranks as the eighth most abundant element in the Earth’s crust and seventh most abundant element in the human body. Barium and beryllium are poisonous and radium, being radioactive it’s exposure is harmful to humans.
Each of the six alkaline earth metals in Group II is unique and has different usages. Some are found in the human body, whereas others are harmful to the human body but useful for other purposes like radioactive processes and so on. These six metals also burn with distinctive flames and have unique flame coloration, which is why they are used in fireworks.