Alkaline earth metals are the elements in the periodic table that have 2 valence electrons in their atoms. The elements Be, Mg, Ca, Sr, Ba, and Ra form the 2nd group of the periodic table and are known as the alkaline earth metals. These elements are placed in the second group of the periodic table as they have only 2 valence electrons. The alkaline earth metals mostly form ionic compounds but are less ionic than the alkali metals. The reason behind it is a smaller size and increased nuclear charge. Be and Mg form more covalent oxides and compounds compared to that of heavy metals like Ca, Sr, Ba.
General characteristics of alkaline earth metals:
1.Oxides and Hydroxides:
- The alkaline earth metals when heated in the presence of oxygen form monoxide, MO which is basic in nature except for BeO which is amphoteric.
- These monoxides have rock salt structure except BeO.
- Monoxides of alkaline earth metals have a high enthalpy of formation and are very stable to heat.
- They are ionic in nature except for BeO which is covalent.
- When the oxides are added to water they form soluble hydroxides except for BeO.
- The characteristics like solubility, thermal stability and the basic character of the hydroxides increase with an increase in atomic number.
- All the halides of alkaline earth metals are ionic in nature except beryllium halides. Beryllium halides are generally covalent and soluble in organic solvents.
- In the solid state, Beryllium chloride has a chain structure.
While in the vapor phase BeCl2 appears to form chloro bridged dimer which at high temperatures (about 1200 k) turns into a linear monomer. While moving down the group, the tendency to form halide hydrates gradually decreases.
- Salts of oxoacids: Alkaline earth metals form salts of oxoacids.
- Carbonates: Alkaline earth metals form carbonates that are insoluble in water and can be precipitated by addition of a sodium or ammonium carbonate solution to a solution of a soluble salt of these metals. With the increase in an atomic number of metal ion, the solubility of carbonates in water decreases. Beryllium carbonate is very unstable in nature, hence it is always kept in an atmosphere of CO2.
- Sulphates: Sulphates of alkaline earth metals are white solids and stable to heat. These are soluble in water. BeSO4 and MgSO4 are readily soluble in water, but solubility decreases from CaSO4 to BaSO4. Sulphates are soluble in water because the high hydration enthalpy of Be2+ and Mg2+ ions overcome the lattice enthalpy factor.
- Nitrates: Nitrates of alkaline earth metals are formed by the dissolution of the carbonates in dilute nitric acid. Nitrates also show a decreasing tendency to form hydrates with increasing the size and decreasing hydration enthalpy. Later on, they decompose on heating to form oxides.
In this article, we read about some of the characteristics of group 2 elements that included the formation of oxides and hydroxides, halides, salts of oxoacids. To know more about the alkaline earth metals, their anomalous behavior and other characteristics, download Byju’s- The Learning App.