The alkaline earth metals are the elements that correspond to Group 2 of the modern periodic table. This group of elements includes beryllium, magnesium, calcium, strontium, barium, and radium. Generally, these elements are silvery-white coloured solids under standard conditions and are highly lustrous (shiny). Additionally, they are quite reactive and have an electronic configuration of ns2. As a result of this configuration, the alkaline earth metals tend to readily lose two electrons to form cations with a charge of +2, making this the most common oxidation state exhibited by these elements.

Table of Contents

Overview of Alkaline Earth Metals

Physical Properties of Alkaline Earth Metals

Ionization Energy of Alkaline Earth Metals

Chemical Properties of Alkaline Earth Metals

Reaction of Alkaline Earth Metals with Water

Reaction of Alkaline Earth Metals with Liquid Ammonia

Anomalous Behaviour of Beryllium

Uses of Alkaline Earth Metals

Answer:

What are Alkaline Earth Metals?

Alkaline Earth Metals are a group of elements in the periodic table that include beryllium, magnesium, calcium, strontium, barium, and radium. They are generally soft, silvery-white metals that are reactive and have low melting points.

Elements whose atoms have their s-subshell filled with their two valence electrons are referred to as alkaline earth metals. Their general electronic configuration is [Noble gas] ns². These elements occupy the second column of the periodic table and are also known as group two metals.

Examples of Alkaline Earth Metals:

• Beryllium (Be)
• Magnesium (Mg)
• Calcium (Ca)
• Strontium (Sr)
• Barium (Ba)
• Radium (Ra)

Also Read:

Alkali Metals

S-Block Elements

The alkaline earth metals occupy successive periods from first to seven, and radium is a radioactive element. These metals form amalgams with mercury.

Overview of Alkaline Earth Metals

| Metals | Beryllium | Magnesium | Calcium | Strontium | Barium |

| Atomic Number | 4 | 12 | 20 | 38 | 56 |

| Configuration | He$2s^2$ | Ne$3s^2$ | Ar$4s^2$ | Kr$5s^2$ | Xe$6s^2$ |

| Abundance (ppm) | 6 | 20900 | 36300 | 300 | 250 |

| Atomic Size (pm) | 112 | 160 | 197 | 215 | 222 |

| Density (g/cm³) | 1.85 | 1.74 | 1.55 | 2.63 | 3.62 |

| Ionization Energy (kJ/mol) | 899 & 1757 | 737 & 1450 | 590 & 1146 | 549 & 1064 | 503 & 965 |

| Hydration Enthalpy (kJ/mol) | -506 | -406 | -330 | -310 | -276 |

| Reduction Potential (V) | -1.7 | -2.37 | -2.87 | -2.89 | -2.9 |

| Flame Colour | Brick Red | Crimson Red | Apple Green |

Physical Properties of Alkaline Earth Metals

Down the column, nuclear charge increases and a new orbital is added to each alkaline earth atom.

Atomic and Ionic Radii

Ionic and Atomic radius decreases down the column of the periodic table, both radii will be larger than the alkali metal and smaller than other atoms of the same period due to charge and addition of the electron to the same energy level.

The cationic radius of alkaline earth elements is smaller than the neutral atom, however the ionic radii increase down the column. For Example, RBe²⁺ < RMg²⁺ < RCa²⁺ < RSr²⁺ < RBa²⁺

How do Alkaline Earth Metals Differ from Alkali Metals in Terms of Density?

Due to their smaller radii, the volume of alkaline earth metal atoms is also smaller. Furthermore, with two valence electrons, these atoms have stronger metallic bonding than alkali metals. As a result, alkaline earth metals have higher density and are harder than alkali metals. See here for more information on metallic bonds.

Density generally increases from magnesium to radium, with calcium having the lowest density among the alkaline earth metals.

Ionization Energy

Alkaline earth elements can donate both valence electrons in order to obtain a noble gas configuration of octet configuration. As a result, they possess two ionization energies.

First Ionization Energy

The first ionization energy of alkaline earth metals is the energy required to remove the first electron from the neutral atom. It is higher than that of the alkali metal atom due to two reasons:

Due to smaller radii, higher nuclear charge holding the electrons tightly, and

Removing an electron from a fully filled and hence stable subshell of an atom.

Second Ionization Energy

In spite of their high ionization energy, the second ionization energy of alkaline earth metals needed for the second electron from the cation is more than the first ionization energy of the atom, but less than any second ionization of alkali metal, making the removal of both electrons feasible.

1. Atom achieves a noble gas configuration

2. The smaller size and higher charge of atoms or ions help to overcome the higher ionization energy by enabling a higher lattice energy due to close packing in solids.

3. Higher Hydration Energy in Liquids due to Larger Solvation

All alkaline earth elements in Group 2 are divalent electropositive metals with a fixed oxidation state of 2. The ionization energy required for the removal of the valence electron is highest for the small beryllium atom.

With an increase in atomic size, the valence electron is shielded by the inner electrons, making it easier to remove with less energy needed. Therefore, the ionization energy decreases as the atomic number or atomic size increases.

IEBe > IEMg > IECa > IESr > IEBa

Note: Due to decreasing ionic size and increasing nuclear charge, ionization energy increases in the same period.

How Does the Solubility of Alkaline Earth Metals Decrease Down the Group?

The solubility of alkaline earth metal ions decreases with increasing size; Beryllium ion is the most soluble, while Barium ion is the least water-soluble. This is due to the ionic nature and size of the ions.

Smaller ions have a higher charge density, which leads to more water molecules being able to solvate them. This results in a higher enthalpy of hydration, making the hydrated ions more stable.

Solubility of Be²⁺ < Solubility of Mg²⁺ < Solubility of Ca²⁺ < Solubility of Sr²⁺ < Solubility of Ba²⁺

Reactivity of Alkaline Earth Metals

As ionization energy decreases down the column from Beryllium to Barium, the reducing ability is expected to increase inversely.

The Reduction potential decreases from beryllium to barium, indicating the increasing reducing capacities. However, the alkaline earth metals are weaker reducing agents than alkali metals due to their higher ionization energy.

Flame Colouration

Except beryllium and magnesium, In Alkaline Earth Metals, the energy needed for an electronic transition between the available energy levels falls in the visible spectrum region. So, on heating, they produce a characteristic colour to the flame reflective of their emission or absorption spectrum and can be used for their identification.

Example: Ca - Brick Red color, Sr - Crimson Red color, and Ba - Apple Green color.

Melting and Boiling Points

The melting and boiling points of the alkaline earth metals, except for magnesium, decrease regularly from beryllium to barium. This is because of their smaller size and strong metallic bonding in close-packed structure, which makes the melting and boiling points of the alkaline earth metals higher than alkali metals.

Chemical Properties of Alkaline Earth Metals

This subsection discusses the key features and general characteristics of compounds of alkaline earth metals.

Hydrides

Beryllium does not react with hydrogen directly; however, Beryllium hydride can be prepared by the reduction of beryllium chloride with lithium aluminium hydride.

2BeCl₂ + LiAlH₄ → 2BeH₂ + LiCl + AlCl₃

Beryllium and magnesium form covalent hydrides in which each hydrogen is connected to two metal atoms. This is an example of molecules with three centres sharing only two electrons, referred to as a “banana Bond”.

Hydrides of Alkaline Earth Metals

Calcium, strontium and barium react with hydrogen to form metallic hydrides. These metallic hydrides give off hydride ions.

M + H₂ → 2MH₂ → M⁺ + 2 H^-

“Hydrolith,” a calcium hydride, is used for producing hydrogen, and it reacts violently with water to release hydrogen.

CaH₂ + 2H₂O → Ca(OH)₂ + H₂

Reaction of Alkaline Earth Metals with Water

Beryllium does not react with water even at higher temperatures, whereas Magnesium reacts with hot water to form hydroxides and releasing hydrogen. Magnesium gets a protecting coat of its oxide, that prevents any further attack by the water molecules. Other alkaline earth metals react with even cold water to liberate hydrogen.

Carbides

Carbides, except for beryllium, react with carbon to form carbides. When these carbides come into contact with water, they liberate acetylene gas, making them a useful source of the gas.

M + 2C → MC2
MC2 + 2H2O → M(OH)₂ + C₂H₂

Oxides

Beryllium reacts with oxygen only above 600°C, while Magnesium and Strontium burn in oxygen to form oxides and Barium forms peroxides.

BeO and MgO are more covalent while the other oxides are ionic. Beryllium oxide is amphoteric, magnesium oxide and calcium oxide are weakly basic, while the other oxides are basic.

Hydroxides

Oxides react with water to ultimately yield hydroxides. The basic nature and thermal stability of hydroxides increases from beryllium to barium.

Carbonates and Bicarbonates

The hydroxides react with carbon dioxide to form carbonates.

M(OH)2 + CO2 → MCO3 + H2O

The solubility of carbonates decreases from Be to Ba while the ionic character and the thermal stability of the carbonates increases from Be to Ba. Bicarbonates are soluble in water and exist only in solution, while carbonates exist as solids and are insoluble in water. In the presence of carbon dioxide, carbonates dissolve by forming bicarbonates.

Sulphates

Contrary to alkali metal sulphates, beryllium sulphate is water-soluble due to its smaller size and higher charge density, which increases its hydration energy. In other sulphates, increasing lattice energy and decreasing hydration energy (due to increasing size) decreases their solubility from BeSO4 to BaSO4.

BeSO₄ > MgSO₄ > CaSO₄ > SrSO₄ > BaSO₄

Nitrates

Nitrates can be prepared by reacting the corresponding oxides, hydroxides and carbonates with nitric acid. Nitrates are soluble in water. On heating, Beryllium nitrate forms nitrite and other nitrates yield oxide, liberating brown fumes of nitrogen dioxide.

2M(NO3)2 → 2M_O + 4NO₂ + O₂

Halides

The exception of beryllium halides is due to more covalent bonding which is caused by the high polarization of the small covalent ion on the electron cloud of the halogen anion, as indicated by Fajan’s Rule.

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

**Properties of Alkaline Earth Metals

The solubility of fluorides in water is negligible, whereas the solubility of other halides decreases with increase in ionic size i.e. from Mg²⁺ to Ba²⁺. Halides are hygroscopic and have the water of crystallization in their solid state (CaCl₂.6H₂O). Fused halides are used as dehydrating agents.

Reaction of Alkaline Earth Metals with Liquid Ammonia

Like alkali metals, Alkaline earth metals also form ammonia solvated cations and electrons. The solution created is electrically conductive, reductive, and paramagnetic. The solvated electrons absorb in the visible region, causing the solution to turn blue. When the solution is concentrated, it takes on a bronze hue. If left to stand for an extended period of time, it will decompose into amide, ammonia, and hydrogen.

M$\ce{(x+y)}$ $\ce{NH3}$ $\rightarrow$ $\ce{[M(NH3)x]+ + [M(NH3)y]–}$ $\rightarrow$ $\ce{MNH2 + 1/2H2}$

Complexes of Alkaline Earth Metals

Beryllium, a smaller alkaline earth metal, forms many complexes with mono, di and tetradentate ligands.

Examples:

• [BeF₃]^-,
• [BeF₄]^2-,
• [Be(H₂C₂O₄)]^2-,
• [Be₄O(R)₆], where R may be NO₃^-, HCOO^-, CH₃COO^- etc.

Anomalous Behaviour of Beryllium

Beryllium has distinct properties from other alkaline earth metals due to its smallest size, highest ionization energy, high electropositive nature and strongest polarizing nature, which gives it a greater covalent nature.

It is the hardest metal among the alkaline earth metals.

Does not react with water even at extremely high temperatures.

The highest melting and boiling point of beryllium is maximum.

It does not react directly with hydrogen to form a hydride.

Unlike other alkaline earth metals, magnesium does not liberate hydrogen from concentrated nitric acid because of its higher electrode potential. This is because the acid forms a coating of oxide, which makes it passive.

Beryllium oxide and hydroxide are amphoteric, meaning they dissolve in acids to form salts and in bases to form beryllates.

Beryllium forms carbide of a different formula and yields methane, unlike other metals which yield acetylene when reacted with water.

Beryllium nitride is highly reactive.

It does not react with atmospheric nitrogen and oxygen.

The Diagonal Relationship Between Beryllium and Aluminum

Beryllium (Be, group 2) and Aluminum (Al, group 3) have similar properties.

Beryl is a mineral composed of beryllium and aluminium, with the formula: 3BeO * Al2O3 * 6SiO2.

Neither of them reacts with atmospheric oxygen and nitrogen.

Neither of them reacts with water even at high temperatures.

On treatment with concentrated nitric acid, they do not liberate hydrogen from acid and become passive.

Both form polyvalent bridged hydrides of a covalent nature.

Both halides have low melting points and are polyvalent and bridged. They are also Lewis acids.

Water hydrolyzes both nitrides, liberating ammonia.

Both oxides and hydroxides of Be and Al are amphoteric, meaning they can react with both acids and bases.

Both form carbide, which upon hydrolysis yields Methane.

Carbonates of beryllium and aluminum are unstable.

Uses of Alkaline Earth Metals

Calcium Carbonate

The pure form of calcite is made by:

First, dissolve the mineral in hydrochloric acid

• Removing hydroxide-forming impurities such as iron and aluminium through the addition of ammonia

Finally, precipitating the calcium carbonate by adding ammonium carbonate.

Limestone when heated breaks down to release carbon dioxide and form quicklime (CaO).

CaCO3 → CaO + CO2

Calcium oxide (quick lime) exothermically reacts with water to form calcium hydroxide (lime water or slaked lime).

CaO + H2O → Ca(OH)2

Plaster of Paris (CaSO4·1/2H2O)

Naturally, available gypsum is calcium sulphate dihydrate (CaSO4. 2H2O) which exists in the monoclinic crystal structure. When an aqueous solution of soluble calcium salts, such as nitrates or chlorides, is treated with dilute sulphuric acid, hydrous calcium sulphate is precipitated out.

On heating in a carbon-free environment (otherwise calcium sulphate is reduced to calcium sulphite), monoclinic gypsum hardens first into another orthorhombic allotropy form, depending on the temperature.

At 120°C: Some of the water of hydration is lost, resulting in the formation of calcium sulphate hemihydrate, also known as Plaster of Paris.

On heating to 200°C: It loses the remaining water and becomes an anhydrous calcium sulphate called “dead burnt Plaster”.

At 400°C: Calcium Sulphate decomposes into Calcium Oxide and Sulphur Dioxide, with Oxygen being evolved.

Properties

A paste of this hemihydrate with about one-third of water sets to a hard mass, in any moulding, in approximately 15 minutes. Additional water may rehydrate the hemihydrate into dihydrate.

Salts like sodium chloride accelerate the hydration process, thus reducing the setting time; whereas, alum or borax slow down hydration, leading to an increase in the setting time of hardening.

It is widely used for decorating surfaces, creating false ceilings, and in medical procedures such as surgery and dentistry.

Alkaline Earth Metals – General Characteristics of Compounds

Extraction of Alkaline Earth Metals

Magnesium Extraction

Magnesium occurs naturally and can be extracted from one of its ores, such as:

Magnesite – MgCO₃

Dolomite - CaMg(CO3)2

Epsomite: MgSO₄·7H₂O

Double Salt of Carnallite: 2KCl·MgCl2·6H2O

Alkaline earth metals have low electrode potentials, and so are obtained by the electrolysis of the fused chlorides. To lower the melting point, chlorides and fluorides of both alkali and alkaline earth metals are added. As magnesium is combustible, a reducing gas like coal gas is maintained during electrolysis.

Frequently Asked Questions (FAQs)

Which group of metals are called alkaline earth metals?

Group 2 elements are called alkaline earth metals. What is the most common oxidation state of alkaline earth metals?

The most common oxidation state of alkaline earth metals is +2.

Group 3 elements are called alkaline earth metals because they have a +2 oxidation state, which is the most common oxidation state among the alkaline earth metals, and they readily lose 2 electrons to achieve the nearest noble gas configuration.

The characteristics of alkaline earth metals include:

• High melting points
• Low electrical conductivity
• High density
• Low reactivity
• High reactivity with halogens
• High solubility in water
• Formation of basic solutions when dissolved in water

No, copper is not an alkaline earth metal.

No, copper is not an alkaline earth metal. It is a transition element.