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Alkaline Earth Metals

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Alkaline Earth Metals are Group 2 elements which includes a collection of elements Beryllium, Magnesium, Calcium, Barium, Strontium, and Radium, which are soft silver metals with a less metallic quality than Group 1 alkali metals. All the heavier metals in Group II such as Ca, Sr, Ba, and Ra, share many features with the Group 1 Alkali Metals.

In this article, we will learn about Alkaline Earth Metals and all the other topics associated with them like their examples, physical properties as well chemical properties. We will also discuss the position of Alkaline Earth Metals in the periodic table. Let’s start learning about this concept of “Alkaline Earth Metals”

What are Alkaline Earth Metals?

Alkaline Earth Metals are a set of six chemical elements in the periodic table’s group 2. Beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra) are the elements involved (Ra). Alkaline Earth Metals are s-block elements as the last electron enter into the s-subshell. At standard temperature and pressure, the elements have extremely similar properties: They are all lustrous, silvery-white, and moderately reactive metals. All of the known alkaline earth metals are found in nature, though radium is only found as a byproduct of the decay of uranium and thorium, rather than as a primordial element.

Because the alkaline earth metals’ valence shells have a completely full s-orbital, they quickly shed two electrons to form cations with a charge of +2. As a result, the alkaline earth metals’ most common oxidation state is +2. They have also known as group two metals since they are found in the second column or group of the periodic table. Group 2 elements are also called Alkaline Earth Metals as their compounds are alkaline in nature.

The general electronic configuration of outer shell of Alkaline Earth Metals is ns2.

Examples of Alkaline Earth Metals

The six alkaline earth metals or group 2 elements are:

  • Beryllium (Be)
Atomic Number Atomic Mass (amu) Electron Configuration

4

9.012

[He]2s²

  • Magnesium (Mg)
Atomic Number Atomic Mass (amu) Electron Configuration

12

24.305

[Ne]3s²

  • Calcium (Ca)
Atomic Number Atomic Mass (amu) Electron Configuration

20

40.078

[Ar]4s²

  • Strontium (Sr)
Atomic Number Atomic Mass (amu) Electron Configuration

38

87.62

[Kr]5s²

  • Barium (Ba)
Atomic Number Atomic Mass (amu) Electron Configuration

56

137.327

[Xe]6s²

  • Radium (Ra)
Atomic Number Atomic Mass (amu) Electron Configuration

88

226

[Rn]7s²

Alkaline Earth Metals on Periodic Table

Alkaline Earth Metals are placed in the second group of the modern-day periodic table, which is shown in the illustration below:

Alkaline-Earth-Metals

Physical Properties of Alkaline Earth Metals

The following table covers all the major physical parameters of alkaline earth metals:

Property

Beryllium (Be)

Magnesium (Mg)

Calcium (Ca)

Strontium (Sr)

Barium (Ba)

Radium (Ra)

Atomic Number

4

12

20

38

56

88

Atomic Mass (amu)

9.01218

24.305

40.078

87.62

137.327

226

Melting Point (°C)

1278

650

842

769

727

700

Boiling Point (°C)

2970

1090

1484

1384

1845

1737

Density (g/cm³)

1.85

1.738

1.54

2.64

3.62

5.5

Colour

Grayish-White

Silver

Silver

Silver

Silver

Shiny White

State at Room Temp.

Solid

Solid

Solid

Solid

Solid

Solid

Electronegativity 
(Pauling scale)

1.57

1.31

1.00

0.95

0.89

0.9

Crystal Structure

Hexagonal

Hexagonal

Cubic

Face-centered 
cubic (FCC)

Body-centered 
cubic (BCC)

Body-centered 
cubic (BCC)

Atomic Radius (pm)

112

160

197

215

222

215

Oxidation States

+2

+2

+2

+2

+2

+2

Ionic Radius (pm)

31

72

100

118

135

147

First Ionization Energy 
(kJ/mol)

899

737

590

549

502

509

Second Ionization Energy (kJ/mol)

1757

1451

1145

1064

965

979

Solubility in Water

High

Moderate

Low

Very Low

Very Low

Very Low

Reactivity

Less Reactive

Moderately Reactive

Reactive

More 
Reactive

Very 
Reactive

Most 
Reactive

Let’s discuss these properties in detail:

Atomic and Ionic Radii

Both ionic and atomic radius decreases down the periodic table column due to charge and the addition of an electron to the same energy level, making them smaller than alkali metals and larger than other atoms of the same period. In alkaline earth elements, both s-electrons can be lost, making them doubly positive cationic. The radius of a cationic atom is lower than that of a neutral atom. Ionic radii continue to rise as you progress down the column.

Be+2 ˂ Mg+2 ˂ Ca+2 ˂ Sr+2 ˂ Ba+2

Density

Because the radius of the atoms is smaller, the volume of the atoms is also less. Furthermore, atoms have stronger metallic bonding due to the presence of two valence electrons. Thus, alkaline earth metals are denser and tougher than alkali metals. The density of alkaline earth metals generally increases from magnesium to radium, with calcium having the lowest density.

Ionization Energy

Ionization energy refers to the energy required to eject the electrons from outermost shell of an atom. Alkaline earth elements can transfer both of their valence electrons to form an octet noble gas configuration. They have two ionization energies as a result:

The first ionisation energy of alkaline earth metals is the energy required to remove the first electron from a neutral atom. It is larger than the alkali metal atom due to smaller radii and the electrons being held tightly by the higher nuclear charge, as well as electrons being withdrawn from a fully filled and so stable subshell.

The second ionisation energy required for the removal of 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. 

Solubility

Beryllium ion is the most water-soluble alkaline earth metal ion, and its solubility diminishes with increasing size, making Barium ion the least water-soluble. A substance’s solubility in water is affected by its ionic composition and size. Smaller ions have a higher charge density and can be dissolved by more water molecules. This increases the enthalpy of hydration and makes the hydrated ions more stable.

Solubility of Be+2 > Solubility of Mg+2 > Solubility of Ca+2 > Solubility of Sr+2 > Solubility of Ba+2

Learn More, Periodic Table Trends

Chemical Properties of Alkaline Earth Metals

There are various chemical properties of alkaline earth metals, some of which are discussed as follows:

Hydrides

Beryllium does not react immediately with hydrogen. The reduction of beryllium chloride with lithium aluminium hydride yields Beryllium Hydride. Beryllium and Magnesium produce covalent hydrides, which have two metal atoms linked to each hydrogen. Banana Bond is an example of a molecule with three centres sharing just two electrons.

Reaction with Water

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

Sulfates

Unlike alkali metal sulphates, Beryllium Sulfate is water-soluble. The hydration energy of beryllium sulphate increases as its size and charge density decrease, resulting in increased solubility. Other sulphates’ solubility falls from BeSO4 to BaSO4 when lattice energy increases and hydration energy reduces (due to increased size).

Anomalous behaviour of Beryllium

Because of its small size, high ionization energy, high electropositive nature, and greatest polarizing nature, Beryllium has a stronger covalent character. Beryllium’s characteristics set it apart from other alkaline earth metals. The anomalous properties of Beryllium is listed below:

  • Among alkaline earth metals, it is the hardest.
  • Even at extremely high temperatures, it does not react with water.
  • Beryllium has the highest melting and boiling points.
  • It does not create hydride when it comes into contact with hydrogen.
  • Because of its higher electrode potential, it does not liberate hydrogen from acid like other alkaline earth metals. Concentrated nitric acid forms an oxide layer that renders it inactive.
  • Oxide and hydroxide of amphoteric beryllium It forms salts when dissolved in acids and beryllate when dissolved in bases.
  • Beryllium generates a carbide with a distinct formula when it reacts with water, yielding methane rather than acetylene like other metals.
  • Beryllium nitride is a flammable material.
  • It doesn’t react with nitrogen or oxygen in the air.

Diagonal Relationship of Beryllium with Aluminium

If we carefully observe the position of Beryllium with Aluminium then we see that they are diagonally placed in the periodic table and have some common properties among them. This is called Diagonal Relationship. Let’s see what are the common properties among Beryllium and Aluminium.

  • Both are unaffected by ambient oxygen and nitrogen.
  • Even at high temperatures, neither of them reacts with water.
  • They don’t let hydrogen out of the acid. They become passive after being treated with strong nitric acid.
  • Both produce polyvalent covalent bridged hydrides.
  • Both have polyvalent, bridging halides with low melting points. Lewis acids are halides.
  • Both nitrides are hydrolyzed by water, releasing ammonia.
  • Be and Al oxides and hydroxides are amphoteric. As a result, they react with both acid and base.
  • Both produce carbide, which is hydrolyzed to produce methane.
  • Aluminum and beryllium carbonates are both unstable.

Alkaline Earth Metals vs Alkali Metals

The key differences between alkali metals and alkaline earth metals are listed in the following table:

Property

Alkaline Earth Metals

Alkali Metals

Group in the Periodic Table

Group 2 (IIA) Group 1 (IA)

Number of Valence Electrons

2 1

Electronic Configuration

ns² ns¹

Reactivity

Less reactive than alkali metals Highly reactive

Oxidation State

Typically +2 Typically +1

Density

Relatively higher Relatively lower

Melting Point

Higher Lower

Boiling Point

Higher Lower

Hardness

Harder Softer

Examples

Magnesium (Mg), Calcium (Ca), 
Strontium (Sr), Barium (Ba),
Radium (Ra)
Lithium (Li), Sodium (Na), 
Potassium (K), Rubidium (Rb),
Cesium (Cs), Francium (Fr)

Uses of Alkaline Earth Metals

Alkaline earth metals find numerous applications in various fields due to their unique properties. Here are some common uses of alkaline earth metals:

Beryllium (Be)

  • Aerospace Industry: Beryllium is used in various aerospace components due to its high strength-to-weight ratio and resistance to fatigue and corrosion.
  • Nuclear Industry: Beryllium is used as a neutron reflector and moderator in nuclear reactors.

Magnesium (Mg)

  • Alloying Agent: Magnesium is often alloyed with other metals to improve its strength, lightweight properties, and corrosion resistance. For example, it is used in the aerospace and automotive industries to make lightweight alloys.
  • Flares and Fireworks: Magnesium is used to produce bright, white light in flares and fireworks as Magnesium is burned it emits a bright white light.
  • Desulfurization: Magnesium is employed in the desulfurization of iron and steel, helping to remove sulfur impurities during the metal refining process.

Calcium (Ca)

  • Metallurgy: Calcium is used as a reducing agent in the production of various metals, such as uranium and thorium.
  • Building Materials: Calcium compounds, such as calcium carbonate (limestone), are widely used in construction for making cement, mortar, and concrete.
  • Dietary Supplement: Calcium is an essential nutrient for human and animal health, and calcium supplements are commonly used to maintain bone health.

Barium (Ba)

  • X-Ray Imaging: Barium compounds, like barium sulfate, are used as contrast agents in X-ray examinations of the digestive system to visualize the gastrointestinal tract.
  • Fireworks: Barium salts are used to produce green colours in fireworks.

Strontium (Sr)

  • Fireworks: Strontium compounds are used to produce red colours in fireworks.
  • Pyrotechnics: Strontium salts are used in pyrotechnics and flares due to their bright red flame.

Radium (Ra)

  • Historical Use: In the past, radium was used in luminous paints for watch dials and instrument panels. However, due to its radioactivity, it is no longer used for such purposes.

Read More

Sample Questions on Alkaline Earth Metals

Question 1: Name the elements which are called alkaline earth metals.

Answer:

Beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra) are alkaline earth metals (Ra).

Question 2: Why are alkaline earth metals harder than alkali metals?

Answer:

Because the radius of the atoms is smaller, the volume of the atoms is also less. Furthermore, atoms have stronger metallic bonding due to the existence of two valence electrons. As a result, alkaline earth metals are denser and tougher than alkali metals.

Question 3: Why is the melting and boiling point of alkaline earth metals more than alkali metals?

Answer:

The melting and boiling temperatures of alkaline earth metals are higher than alkali metals due to their smaller size and strong metallic bonding in a close-packed structure.

Question 4: How do alkaline earth metals react with water?

Answer:

Even at higher temperatures, beryllium does not react with water. Magnesium only reacts with hot water to form hydroxides and emit hydrogen. Magnesium receives a protective coat of oxide, which prevents further attack by water molecules. Other alkaline earth metals release hydrogen when they react with even cold water.

Question 5: What is a banana bond?

Answer:

Beryllium and magnesium combine to form covalent hydrides, in which each hydrogen is linked to two metal atoms. This is known as a banana bond.

FAQs on Alkaline Earth Metals

1. Define Alkaline Earth Metals.

The alkaline earth metals are a set of six chemical elements in the periodic table’s group 2

2. What are the Properties of Alkaline Earth Metals?

Alkaline Earth Metals possess 2 valence electrons, low electronegativity, increasing reactivity down the group, higher melting points, and form +2 cations.

3. How are Alkaline Earth Metals arranged on the periodic table?

Alkaline Earth Metals are arranged on the second group of the periodic table.

4. Can you provide examples of Alkaline Earth Metals?

Some examples of Alkaline Earth Metals are Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), and Radium (Ra).

5. How do Alkaline Earth Metals differ from Alkali Metals?

Alkaline Earth Metals have higher melting points and densities, and form +2 cations, while Alkali Metals have lower melting points, are more reactive, and form +1 cations.


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Last Updated : 25 Aug, 2023
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