S-Block Elements

On the Periodic Table, the members of this block are located on the far left hand side of the table. The elements with the ns1 configuration are referred to as alkali metals (Group IA elements), whereas the elements with the ns2 configuration are referred to as alkaline earth metals (Group IIA elements). The elements of the s-block are referred to as reactive metals in some circles.

The Characteristics of S-Block Elements

The elements in Groups 1 and 2 of the modern periodic table are referred to as s-block elements because they are grouped together. In the s-subshell of a s block element, there are two types of s block elements that can exist: elements with a single electron (s1) and elements with two electrons.

There are 14 elements in the S-block, including hydrogen (H), lithium (Li), helium (He), sodium (Na), beryllium (Be), potassium (K), magnesium (Mg), rubidium (Rb), calcium (Ca), cesium (Cs), strontium (Sr), francium (Fr), barium (Ba), and radium (Ra).

Both alkali and alkaline earth elements exhibit a regular gradation in their properties when compared to the other elements in their respective groups. However, the first member of both s block elements, namely, Lithium and Beryllium, differs significantly from the rest of their members while also resembling the diagonal element present in the following column.

The anomaly of these S-block elements can be attributed to the following

Atomic and ionic sizes that are small

A higher charge density (the ratio of charge to the volume of the atom) is desirable.

A greater degree of polarisation

There are no d-orbitals present.

Increased polarisation of s block elements makes the first element more covalent and distinguishes it from the rest of the elements, which are all ionic in nature.

Because of their similarity in size and charge density, they are reminiscent of the element diagonally placed in the following group (diagonal relationship).

Observations have been made that the physical and chemical properties of these s block elements change in a predictable manner as the atomic number of the elements rises. Changes in the group’s various properties are being observed.

When the s block elements of the modern periodic table are examined, it is discovered that the size of the alkali metals is larger when compared to the size of the other elements in a given time period. As the atomic number increases, the total number of electrons increases, as does the number of shells added to the atoms. 

As you move down the group, the atomic number gets higher and higher. A consequence is that the atomic and ionic radius of alkali metals grows.

Enthalpy of Ionisation

In order to progress down the group, the size of the atoms grows in proportion to the increase in their number, resulting in a decrease in attraction between the nucleus and electrons in the outermost shell. The ionisation enthalpy decreases as a result of this process. The ionisation enthalpy of alkali metals is lower than that of other elements, which is a significant difference.

Enthalpy of Hydration

The hydration enthalpy of the elements decreases as the ionic sizes of the elements increase. Because of the high charge/radius ratio of the atom, the hydration enthalpy increases as the size of the ion decreases. This is because the atom has the capacity to accommodate a greater number of water molecules around it and thus becomes hydrated.

Physical Characteristics of s-Block Components

Throughout the s block elements, the density of alkali metals increases as you progress through the group. The density of potassium is lower than the density of sodium, which is an exception.

Because of the weak metallic bonding between the alkali metals, their melting and boiling points are extremely low.

The ability of alkali metals and their respective salts to impart colour to an oxidising flame is due to the heat generated by the flame, which excites the valence electrons from one energy level to another energy level, and the ability of alkali metals and their respective salts to impart colour to an oxidising flame. During the flame test, this aids in the detection of alkali metals, which is beneficial.

Conclusion

Because there are no electrons in the shells of the elements in Group IA, their atomic radii are the largest. As a result, the ionisation potential of these elements is the lowest. They react with water to form the corresponding alkalis in the solution. Alkali metals are so named because of the characteristics of the s block elements that make them.