Physical and Chemical Behaviour of Alkaline Earth Metal

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What is Alkaline Earth Metal?

The elements that constitute group 2 of the modern periodic table are known as alkaline earth metals. Alkaline earth metals are atoms that have their s-subshell packed with two valence electrons. [Noble gas] ns2 is their electronic configuration in general. They are also known as group two metals because they are found in the second column of the periodic table.

 Members of Alkaline Earth Metals Include:

  1. Beryllium

  2. Magnesium

  3. Calcium

  4. Strontium

  5. Barium

  6. Radium 

The physical and chemical properties of the elements in this group are very similar. This article will study alkaline earth metal physical and chemical behaviour in detail.


Physical and Chemical Behaviour


Atomic and Ionic Radii

Due to charge and the addition of an electron to the same energy level, both ionic and atomic radius decreases down the periodic table column, making them smaller than alkali metals and larger than other atoms of the same age.

Both s-electrons can be lost in alkaline earth elements, making them doubly positive cationic. The radius of a cationic atom is less than that of a neutral atom. Ionic radii continue to increase as you go down the column.


Ionization Energy

Alkaline earth elements can donate all of their valence electrons to form an octet noble gas configuration. They have two ionisation energies as a result:


First Ionisation Energy

The energy required to remove the first electron from a neutral atom is known as the first ionisation energy of alkaline earth metals. Because of smaller radii and the electrons being retained closely by the higher nuclear charge, it is greater than that of an alkali metal atom. Electrons are withdrawn from a completely filled and thus stable subshell.


Second Ionisation Energy

The second ionisation energy needed for the second electron from the cation in alkaline earth metals will be higher than the atom's first ionisation energy, but lower than any alkali metal's second ionisation energy. Despite the strong ionisation energy, both electrons may be removed since the atom:

  1.  Adopts a noble gas configuration.

  2. Because of the tight packing of atoms or ions in solids, the smaller size and higher charge help overcome the higher ionisation energy by increasing the lattice energy.

  3. Due to greater solvation, liquids have higher hydration energy.

So alkaline earth elements in group two are all divalent electropositive metals with a set oxidation state of 2. The tiny beryllium atom would need the most ionisation energy to remove the valence electron.

The valence electron is protected by the inner electrons as the atomic size increases, making it easier to remove with less energy. As a result, as the atomic number or size increases, the ionisation energy decreases.


Reactivity of Alkaline Earth Metals

Ionization energy is inversely proportional to reducing ability. From Beryllium to Barium, the reducing property is supposed to increase as the ionisation energy decreases down the column.

From beryllium to barium, the reduction potential decreases, suggesting rising reducing capacities. Due to their higher ionisation energy, alkaline earth metals are weaker reducing agents than alkali metals.


Flame Colouration

The energy required for an electronic transition between available energy levels in Alkaline Earth Metals is in the visible spectrum. As a result, all metals, except beryllium and magnesium, develop a distinct colour in the flame that reflects their emission or absorption spectrum and can be used to identify them when heated.


Melting and Boiling Points

The melting and boiling points of alkaline earth metals are higher than alkali metals due to their smaller size and strong metallic bonding in a close-packed system. Except for magnesium, the melting and boiling points of alkaline earth metals decrease in order from beryllium to barium.


Alkaline Earth Metal Physical and Chemical Behaviour

This subsection discusses the main characteristics of alkaline earth metal compounds as well as their general characteristics.


Hydrides 

Beryllium does not react directly with hydrogen. The replacement of beryllium chloride with lithium aluminium hydride yields beryllium hydride.

2BeCl2 + LiAlH4 → 2BeH2 + LiCl + AlCl3

Beryllium and magnesium form covalent hydrides, which have two metal atoms bound to each hydrogen. The "banana Bond" is a type of molecule in which three centres share just two electrons.

Metallic hydrides are formed when calcium, strontium, and barium react with hydrogen. Hydrides ions are generated by metallic hydrides.

M + H2 → 2MH2 → M+ + 2 H-

Hydrogen is formed when hydrides react violently with water. Hydrogen is produced using a calcium hydride called "Hydrolith."

CaH2 + 2H2O → Ca(OH)2 + H2


Reaction of Alkaline Earth Metals with Water

Also at higher temperatures, beryllium does not react with water. Magnesium only forms hydroxides and releases hydrogen as it reacts with hot water. Magnesium receives a protective coat of its oxide, which protects it from further water molecule attack. Other alkaline earth metals produce hydrogen when they react with even cold water.


Carbides

Except for beryllium, alkaline earth metals and their oxides react with carbon to form carbides. Carbides are used as a source of acetylene gas because they react with water to produce it.


Oxides

Beryllium only reacts with oxygen at temperatures above 600°C. Magnesium and strontium form oxides when exposed to oxygen, while barium forms peroxides.

The covalent oxides BeO and MgO are more so than the ionic oxides. Amphoteric beryllium oxide, weakly basic magnesium oxide, and basic calcium oxide, while other oxides are basic.


Hydroxides

Hydroxides are formed when oxides react with water. From beryllium to barium, the basic nature and thermal stability of hydroxides change.


Carbonates 

Carbonates are formed when hydroxides react with carbon dioxide.

M(OH)2 + CO2 → MCO3+ H2O

Bicarbonates are water-soluble and only occur in solution. In water, carbonates are stable and insoluble. Carbonates' solubility decreases from Be to Ba. Carbonates degrade into bicarbonates in the presence of carbon dioxide. From Be to Ba, the carbonates' ionic character and thermal stability increase.


Sulphate 

Beryllium sulphate, unlike alkali metal sulphates, is water-soluble. The hydration energy of beryllium sulphate increases as its size and a charge density decrease, resulting in increased solubility. Other sulphates' solubility decreases from BeSO4 to BaSO4 as lattice energy increases and hydration energy decreases (due to increasing size).


Nitrates

Nitrates are made by reacting nitric acid with the appropriate oxides, hydroxides, and carbonates. Nitrates are water-soluble. Beryllium nitrate becomes nitrite when heated, while other nitrates become oxide, releasing brown nitrogen dioxide fumes.

2M(NO3)2 → 2MO + 4 NO2 + O2


Halides

Both halogens react with alkaline earth metals from calcium to barium to form strong ionic halides with a definite crystal structure. From fluorine to iodine, reactivity decreases. Because of the strong polarisation of the small covalent ion on the electron cloud of the halogen anion, as suggested by Fajan's law, beryllium halides have more covalent bonding.

Beryllium halides exist as individual molecules in the gas phase, and they form Be-X chains in the solid phase.

Fluorides are water-insoluble. Other halides' solubility decreases as ionic size increases, such as from Mg2+to Ba2+. In their solid-state, halides are hygroscopic and contain the water of crystallisation (CaCl2.6H2O). Dehydrating agents include fused halides.


Reaction of Alkaline Earth Metals with Liquid Ammonia

Alkaline earth metals, including alkali metals, form ammonia solvated cations and electrons. The solution is reductive, electrically conductive, and paramagnetic. The visible region absorbs the solvated electrons, turning the solution blue. Bronze is the colour of the condensed solution. It decomposes into amide, ammonia, and hydrogen after a long period of time.


Complex of Alkaline Earth Metal

Alkaline earth metals are smaller size complexes. Beryllium binds to mono, di, and tetradentate ligands to form a variety of complexes.


Applications of Alkaline Earth Metal

  1. Beryllium is mostly used in military applications, although it has other applications as well. Beryllium is a p-type dopant in some semiconductors used in electronics, and beryllium oxide is a high-strength electrical insulator and heat conductor. Beryllium is also used in mechanics when stiffness, lightweight, and dimensional stability are needed over a broad temperature range due to its lightweight and other properties.

  2. Magnesium has a wide range of applications. It has advantages over other materials such as aluminium, but due to magnesium's flammability, it is no longer widely used. Magnesium is often alloyed with aluminium or zinc to create products with better properties than pure metals. Magnesium is used in a variety of industrial processes, including the manufacture of iron and steel, as well as the production of titanium.

  3. Calcium has a wide range of applications. Its use as a reducing agent in the extraction of other metals from ore, such as uranium, is one of its many applications. It is also used to deoxidize alloys and is used in the manufacture of many metal alloys, including aluminium and copper alloys. Calcium is also used in the production of cheese, mortar, and cement.

  4. Strontium and barium have fewer uses than lighter alkaline earth metals, but they are still useful. Pure strontium is used in the study of neurotransmitter activation in neurons, and strontium carbonate is often used in the manufacture of red fireworks. Radioactive strontium-90 is used in RTGs, which take advantage of its decay heat. Barium is used in vacuum tubes to extract gases, and barium sulphate is used in a variety of industries, including the petroleum industry.


Did You Know?

Due to its small scale, highest ionisation force, high electropositive nature, and best polarising nature, Beryllium has a more covalent nature. Beryllium's properties set it apart from other alkaline earth metals.

  1. Among alkaline earth metals, it is the hardest.

  2. Except at extremely high temperatures, it does not react with water.

  3. Beryllium has the highest melting and boiling points.

  4. It does not form hydride when it comes into contact with hydrogen.

  5. Because of its higher electrode potential, it does not release hydrogen from acid like other alkaline earth metals. Concentrated nitric acid forms an oxide layer that renders it inactive.

  6. Amphoteric beryllium oxide and hydroxide When dissolved in acids, it forms salts, and when dissolved in bases, it forms beryllate.

  7. Beryllium forms a carbide with a different formula when it reacts with water, yielding methane rather than acetylene like other metals.

  8. Beryllium nitride is a flammable material.

  9. It doesn't interfere with nitrogen or oxygen in the air.

FAQs (Frequently Asked Questions)

1. Why are Alkali Metals Denser Than Alkaline Earth Metals?

Ans: Since the radius of the atoms is smaller, the volume of the atoms is also smaller. Furthermore, atoms have greater metallic bonding due to the presence of two valence electrons. As a result, alkaline earth metals are denser and tougher than alkali metals.

The density of alkaline earth metals usually rises from magnesium to radium, with calcium having the lowest density.

2. Why Does the Solubility of Alkaline Earth Metals Decrease as We Move Down the Group?

Ans: Beryllium ion is the most water-soluble alkaline earth metal ion, and its solubility decreases with increasing size, making Barium ion the least water-soluble. The ionic composition and size of a substance affect its solubility in water.


Smaller ions have a higher charge density and can be dissolved by a greater number of water molecules. This increases the hydration enthalpy and makes the hydrated ions more stable.

3. Why Do Alkaline Earth Metals Have Similar Chemical Properties?

Ans: Since they all have two valence electrons, alkaline Earth metals have identical properties. They readily give up their two valence electrons in order to obtain the most stable electron configuration, the maximum outer energy stage. Just one valence electron exists in alkali metals.

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