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S Block Elements On The Periodic Table | Introduction

Updated on 09 September 2021
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IIT JEE Preparation
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Updated on 09 September 2021

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: elements with one electron (s1) in their subshell or elements with two electrons (s2) in their subshell. 


There are 14 elements in the S-Block category. They are listed below:


  1. Hydrogen(H)
  2. Lithium(Li)
  3. Helium(He)
  4. Sodium(Na)
  5. Beryllium(Be)
  6. Potassium(K)
  7. Magnesium(Mg)
  8.  Rubidium(Rb)
  9. Calcium(Ca)
  10. Cesium(Cs)
  11. Strontium(Sr)
  12. Francium(Fr)
  13. Barium(Ba)
  14. Radium(Ra) 


TYPES OF S BLOCK ELEMENTS


The s block elements that have only one electron in their s-orbital are called alkali metals (group 1 elements).


The s block elements that have two electrons in their s-orbital are called alkaline earth metals (group 2 elements). 


Tips - How to learn the periodic table


The electrons present in an atom occupy various sub orbitals as available according to their energy in increasing order. The electron left in the last is placed in one of s, p, d and f sub-shells. The elements whose atoms have their last valence electron in the s-suborbital are called S block elements. 


ELECTRONIC CONFIGURATION OF S BLOCK ELEMENTS


The alkali elements have only one valence electron in their outermost shell. The electron is loose and can bond with other elements. This makes these elements highly electropositive. These elements do not occur in nature in a free state due to their highly reactive nature. 


The electronic configuration of group 1 elements of the S block are given in the table below.


ELEMENT

SYMBOL

ELECTRONIC CONFIGURATION

Lithium

Li

1s22s1

Sodium

Na

1s22s22p63s1

Potassium

K

1s22s22p63s23p64s1

Rubidium

Rb

1s22s22p63s23p63d104s24p65s1

Cesium

Cs

[Xe]6s1

Francium

Fr

[Rn]7s1


The electronic configuration of group 2 elements of the S block are given in the table below


ELEMENT

SYMBOL

ELECTRONIC CONFIGURATION

Beryllium

Be

[He]2s2

Magnesium

Mg

[Ne]3s2

Calcium

Ca

[Ar]4s2

Strontium

Sr

[Kr]5s2

Barium

Ba

[Xe]6s2

Radium

Ra

[Rn]7s2





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PROPERTIES OF S BLOCK ELEMENTS


Both groups of the S block elements show similar properties and gradation but the first element of both alkali metals and alkaline earth metals, namely Lithium and Beryllium show enough difference from the rest of the elements of their respective groups. Both these elements are however similar to the diagonal element in the next column. 

The causes for the peculiar properties of these elements are assigned to the following reasons :

  1. Low atomic and ionic size
  2. Greater charge density
  3. Greater polarization
  4. Absence of d-orbitals.


It is noted that, as the atomic number increases, the chemical and physical properties of these elements change in a certain trend. Let us discuss these changes in detail.


CHEMICAL PROPERTIES OF S BLOCK ELEMENTS


  1. ATOMIC AND IONIC RADII - It is recorded under observation that the alkali metals are larger in size as compared to the other metals in a specific period. As the atomic number increases, new shells are added and the total number of electrons increases. This results in the increase of the atomic and ionic radius of the elements. 


  1. IONIZATION ENTHALPY - As the size of the atom increases due to an increase in atomic radius, the attraction between the nucleus and the electrons in the outermost shell decreases. This in turn results in the decrease of ionization enthalpy. The ionization enthalpy of alkali metals is lesser in comparison to other elements.

 

  1. HYDRATION ENTHALPY - A smaller atom can hold more water due to the high charge to radius ratio and gets more hydrated. As the ionic size of an element increases, its capacity to stay hydrated decreases, so the hydration enthalpy decreases.  


Physical Properties Of S Block Elements


  1. The density of alkali metals increases as we move down the group and the atomic number increases. There is an exception of Potassium here. The density of potassium is less than that of sodium.
  2. Alkali metals have a weak metallic bonding, which makes their melting and boiling points remain low. 
  3. When alkali metals and their respective salts are burnt, they impart colour to the flame. This happens because the heat excites the valence electron from one energy level to another. Hence, flame tests can be done to detect alkali metals. 


Diagonal Relationship Between S Block Elements


There exists a diagonal relationship between the elements that are adjacent to each other and are located in the second and third periods of the periodic table. For example, Lithium in the Second Period is similar to Magnesium located in the Third Period. 


S block elements have very different properties from the other elements of the subgroup they belong to. However, diagonal elements have many similarities in properties. This relationship is showcased as you move left to right and down the group. Let us look at the similarities between these diagonal neighbours in some detail.


Similarities between Lithium and Magnesium


  1. Lithium and Magnesium are harder than other elements in their groups
  2. Chlorides of both Lithium and Magnesium are soluble in ethanol.
  3. Lithium and Magnesium are lighter than other elements in their groups.
  4. Both the elements react with water gently. Oxides and hydroxides are less soluble
  5. Lithium and Magnesium form their respective nitrides in the presence of nitrogen.
  6. When Lithium and Magnesium react with oxygen, they don’t form superoxides.
  7. When carbonates of Lithium and Magnesium are heated, Carbon Dioxide and other oxides are formed. 


Similarities between Beryllium and Aluminium


  1. Both Aluminium hydroxide and Beryllium hydroxide react with excess alkali and form their ions. 
  2. An oxide film is present on the surface of both these metals, which gives them the capacity to get through acid attacks. 
  3. Both Beryllium and Aluminium have the tendency to form complexes
  4. Chlorides of both these elements are soluble in organic solvents.


This is a brief description of the S Block of the modern periodic table. Happy Learning!


S - Block Important Question -


  1. Carbonates of lithium are not stable like that of sodium due to
  2. Li is different from its family members due to
  3. Which element is necessary for normal leaf development?
  4. The oxides of beryllium BeO is
  5. The formula of Chile saltpetre is


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