S-Block Elements
The elements of Group 1 and Group 2 of the modern periodic table are called S-block elements. There are two types of s block elements in Periodic table, the elements with one electron (s1) or the elements with two electrons (s2) in their s-subshell.
There are 14 elements in S- Block in
periodic table which names are: Hydrogen (H), Kithium (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).
What is S-Block Elements?
Group one, also known as alkali metals, refers to s-block elements with just one electron in their s-orbital, whereas group two, also known as alkaline earth metals, refers to s-block elements with two electrons in their s-orbital.
All of the reactive metals in the S-block have low ionisation enthalpies. They easily shed the outermost electron(s) to create a 1+ ion or a 2+ ion (in the case of alkali metals) (in the case of alkaline earth metals). As we descend the group, the metallic quality and reactivity get stronger. They are never found pure in nature due to their extreme sensitivity. With the exception of lithium and beryllium, the s-block elements' compounds are primarily ionic.
In order of increasing energy, the electrons
in an atom occupy different sub-orbitals of the accessible energy levels. An
atom's last electron may be found in one of the s, p, d, or f subshells. As a
result, the atom's elements with their last valence electron in the
s-suborbital are referred to as s block elements.
Electronic Configuration of S-Block Elements
The s-block alkali elements only have one valence electron in their outermost shell. These metals are extremely electropositive due to the loosely held outermost electron. They cannot be found in nature's free state as a result.
The table below shows the general electrical
configurations of group 1 s block elements:
|
Element |
Symbol |
Atomic Number |
Electronic Configuration |
|
|
Lithium |
Li |
3 |
1s²2s¹ |
1 |
|
Sodium |
Na |
11 |
1s²2s²2p⁶3s1 |
1 |
|
Potassium |
K |
19 |
1s²2s²2p⁶3s²3p⁶4s¹ |
1 |
|
Rubidium |
Rb |
37 |
1s²2s²2p⁶3s²3p⁶3d¹⁰4s²4p⁶5s¹ |
1 |
|
Cesium |
Cs |
55 |
[Xe]6s¹ |
1 |
|
Francium |
Fr |
87 |
[Rn]7s¹ |
1 |
The following table illustrates the
electrical arrangements of the S block element group 2 elements:
|
Elements |
Symbols |
Atomic Number |
Electronic Configuration |
Valence Electron |
|
Beryllium |
Be |
4 |
[He]2s² |
2 |
|
Magnesium |
Mg |
12 |
[He]2s² |
2 |
|
Calcium |
Ca |
20 |
[Ar]4s² |
2 |
|
Strontium |
Sr |
38 |
[Kr]5s² |
2 |
|
Barium |
Ba |
56 |
[Xe]6s² |
2 |
|
Radium |
Ra |
88 |
[Rn]7s² |
2 |
Properties of S-Block Elements
The characteristics of both alkali and alkaline earth elements exhibit a predictable gradient within each group of elements. However, the first S block members, Lithium and Beryllium, differ significantly from the remainder of their members while also resembling the diagonal element more in the following column.
- These S-block elements' oddity is caused by:
- very small atomic and ionic sizes
- Higher charge density (charge/atom volume)
- heightened polarisation
- There are no d-orbitals.
- The initial s block element becomes more covalent with increased polarisation, setting it apart from the other ionic s block members.
- They resemble the element diagonally positioned in the following group due to their resemblance in size and charge density (diagonal relationship).
As the atomic number of the elements rises,
it is seen that the physical and chemical characteristics of these S-block
elements alter in a certain pattern. The following are changes to the group's
various properties:
Chemical Properties of S-Block Elements
Atomic and Ionic Radii
The alkali metals are larger than other elements in a certain era when the s block elements of the contemporary periodic table are observed. The total number of electrons also rises as the atomic number rises, and shells are also added.
The atomic number rises as you descend the
group. The alkali metals' atomic and ionic radius grows as a result.
Physical Properties of S-Block elements
Atomic and ionic radii: Due to the brittle metallic connection, the alkali metals have a low melting and boiling point.
Because of this, the valence ion's size is always smaller than that of its parent atom after losing an electron.
The created ion's valence shell is totally shattered when the electron is lost.
The effective nuclear charge rises as a result of an increase in the amount of protons relative to electrons, which reduces the size of the ion.
Density: Alkali metals have low densities during their period due to their huge atomic sizes. The density of metals rises as you move from top to bottom in a group due to the increase in atomic mass and size.
One exception is that potassium has a lower density than sodium because of its big size and unfilled d orbitals.
Melting and boiling points: Because alkali metals have one electron in their outermost shell, these metals have low melting and boiling points because weak metallic bonds are discovered between them.
Ionization Enthalpy: Compared to other elements of the same era, alkali metals have an extremely low ionisation enthalpy value. In a group, the ionisation enthalpy falls from top to bottom.
Less energy is needed to remove an electron as an atom grows larger because the distance between the outermost electron and the nucleus grows.
Due to their low ionisation energy, alkali metals have a strong electronegative potential. Alkali metals' second ionisation enthalpy is worth more than their initial ionisation enthalpy.
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