Alkaline Aarth Metals- CBSE Class 12th Science by Unacademy

Introduction

In the periodic table, the first two groups consist of the most electropositive elements like sodium, calcium, potassium, and so on. Out of these two groups, the second one, or Group IIA is termed alkaline earth metals. They are named in such a manner because most elements are available naturally in the form of sulphates, nitrates, carbonates, halides, and more. Also, the term “alkaline” represents that these elements can react with water and form alkalis like magnesium hydroxide, calcium hydroxide, and so on. In this note below, we will discuss these elements in detail, conveying information for both physical and chemical properties so that you can understand them in detail. 

Introduction to the alkaline earth metals

Group 2 or IIA is known as the alkaline earth metal group having six elements- Beryllium (Br), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra). This group derives its name from the occurrence of alkaline compounds of the elements that are found abundantly in nature. 

Electronic configuration 

If we go by the periodic table rules, Group 2 elements will have two free electrons in the outermost subshell. The sub shell’s quantum number will increase down the group but all of them will have the s-orbital. Based on the arrangements, the electronic configurations of all the six alkaline earth metals are as follows: 

1. Beryllium: 2s2
2. Magnesium: 3s2
3. Calcium: 4s2
4. Strontium: 5s2
5. Barium: 6s2
6. Radium: 7s2

Since there are two electrons in the outermost shell, they are also known as diatomic and can form ions with a general structure of A2+.

Occurrence 

The alkaline earth metals are highly reactive and therefore, they aren’t present in free states in nature. Beryllium can’t be found easily and also, its extraction from ores involves a lot of cumbersome processes. On the other hand, magnesium and calcium are present in compound forms abundantly like MgCO3, CaCO3, and so on. Strontium and Barium are also found in nature but not in the form of ores. Radium is radioactive in nature, and therefore, a lot of speculations are there regarding its occurrence in free state. 

Physical properties of the alkaline earth metals

As all the elements have similar electronic configuration of the last orbital, their physical and chemical properties are almost relevant with each other. However, the properties can change as you move down the group.

Atomic and ionic radius

The alkaline earth metals and their respective ions have larger sizes because of the fulfilled state and electron repulsion present in other energy levels. As you move down the group, a new shell will be added and therefore, the distance from the nucleus to the last orbital will increase. Hence, calcium is bigger than magnesium but smaller than Barium. 

Ionization enthalpy

All the alkaline earth metals have larger size and therefore, the nuclear force of attraction between the last two electrons and protons is less in magnitude. Therefore, they are loosely held and on application of a little amount of heat or energy, these two electrons will immediately leave their orbitals, thereby forming diatomic cations. However, the electrons leave one after the other. So, for Group IIA elements, their overall ionization enthalpy is less. But the ionization enthalpy of the second electron is greater than the first. 

Electron affinity 

The alkaline earth metals have fulfilled the s-orbital state with two electrons. Therefore, they have very little affinity for an incoming electron which is why they are said to be electropositive elements. 

Chemical bond 

By losing two electrons and forming a diatomic ion, the alkaline earth metals can form ionic compounds with strong chemical bonds between the participating ions. For example, calcium carbonate is an ionic compound formed when a calcium atom loses two electrons for fulfilling the last orbital of the carbonate ion.

Reducing agents 

During any chemical reaction involving the Group IIA elements, the atoms easily lose the outermost orbital electrons and form ionic compounds. Due to the loss of electrons, they are said to be strong reducing agents and their oxidation number is +2. 

Chemical properties of the alkaline earth metals 

The alkaline earth metals are highly reactive and therefore, they can react with different elements and compounds like water, halogens, carbonates, phosphates, and more. 

Reaction with water

When the Group 2 electrons react with water, they form hydroxides and oxides. For example:

1. Ca + H2O –🡪 Ca(OH)2 + H2
2. Mg + H2O -🡪 MgO + H2

These reactions are exothermic and therefore, a high amount of heat is generated along with the formation of hydrogen gas.

Reaction with acids 

The alkaline earth metals can also react with acids to form salts and release hydrogen gas. For example: 

1. Ca + H2SO4 -🡪 CaSO4 + H2
2. Mg + HCl –🡪 MgCl2 + H2
3. Ca + H3PO4 –🡪 Ca3(PO4)2

Reaction with oxygen

These elements have high reactivity with oxygen and can form metallic oxides with ease. Beryllium, calcium, and magnesium form monoxides while barium and strontium form dioxides. 

1. 2Be + O2 -🡪 2BeO
2. 2Mg + O2 -🡪 2MgO
3. 2Ca + O2 -🡪 2CaO
4. Sr + O2 -🡪 SrO2
5. Ba + O2 -🡪 BaO2

Metallic hydrides 

Being electropositive elements, these alkaline earth metals can easily react with hydrogen to form the respective metallic hydrides like: 

1. Ca + H2 –🡪 CaH2
2. Mg + H2 –🡪 MgH2

However, Beryllium cannot react with hydrogen-like the above elements. Rather, its compound, Beryllium chloride, reacts with lithium aluminum hydride to form Beryllium hydride, aluminum trichloride, and Lithium chloride. 

Formation of metallic halides 

Another most important chemical property of the alkaline earth metals is the formation of halides after reacting with the halogen elements.’

1. Ca + 2HCl –🡪 CaCl2 + H2
2. Mg + 2HCl –🡪 MgCl2 + H2

Diagonal relationship of Beryllium 

One of the most important facts about the Group 2 elements is the diagonal relation of Beryllium with Aluminium of Group 2. They show almost the same behaviour due to the electronic configurations. 

Conclusion 

The alkaline earth metals are highly reactive and therefore, they can form a wide range of compounds through different reactions. From carbonates to halides, nitrides, oxides, and hydrides, these elements can take part in displacement reactions and double decomposition reactions. Beryllium has a lot of anomalies and in many cases, it does not follow the trend in chemical properties of other elements belonging to the same group. As for radium, the chemical reactions of this element are yet to be known because of its unstable nucleus. Calcium and magnesium are the two most important alkaline earth elements that can form a wide range of compounds and have found their use in inorganic chemistry extensively.