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Group 2 Elements: Alkaline Earth Metals

  • Last Updated : 29 Nov, 2021

Beryllium, Magnesium, Calcium, Barium, Strontium, and Radium are Group 2 alkaline earth metals, which are soft silver metals with a less metallic quality than Group 1 alkali metals. Although the heavier metals, such as Ca, Sr, Ba, and Ra, share many features with the Group 1 Alkali Metals, they are virtually as reactive. The valence shells of all elements in Group 2 have two electrons, giving them an oxidation state of +2.

Group 2 Elements: Alkaline Earth Metals

The 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). 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, albeit 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 of the periodic table.

The general electronic configuration of these elements is ns2.

Physical Properties of Alkaline Earth Metals

  • 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

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 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 greater ionisation energy, both electrons can be removed because the atom assumes a noble gas configuration, and the smaller size and higher charge help overcome the higher ionisation energy by generating higher lattice energy due to the close packing of atoms or ions in solids. Also, because of the larger solvation, liquids have higher hydration 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

  • Reactivity

Ionization energy is inversely proportional to reducing ability. From Beryllium to Barium, the reducing characteristic is projected to grow as the ionisation energy lowers along the column. From beryllium to barium, the reduction potential drops, indicating increased reducing capabilities. Alkaline earth metals are poorer reducing agents than alkali metals due to their higher ionisation energy.

  • Melting and Boiling Points

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. Except for magnesium, the melting and boiling temperatures of alkaline earth metals fall in order from beryllium to barium.

Chemical Properties of Alkaline Earth Metals

  • 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.

  • Sulphates

Unlike alkali metal sulphates, beryllium sulphate 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 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, highest ionisation energy, high electropositive nature, and greatest polarising nature, Beryllium has a stronger covalent character. Beryllium’s characteristics set it apart from other alkaline earth metals.

  • 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

  • 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.

Sample Questions

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.


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