Block Elements (Alkali and Alkaline Earth Metals)

The s- block elements of the periodic table are the ones in which the last electron enters the outermost s orbital. As this particular orbital can accommodate only two electrons, two groups (1 and 2) belong to the s- block itself. Group 1 consists of elements like sodium, potassium, lithium, rubidium, francium, and caesium. These are known as alkali metals. Moreover, Group 2 includes elements like magnesium, beryllium, strontium, calcium, radium, and barium. These are the alkaline earth metals. The p- block elements of the periodic table are the ones in which the last electron enters the outermost p orbital. There are three p orbitals that can accommodate a maximum number of six electrons.

Group 1 – Alkali Metals

Atomic properties

• Electronic configuration: All these metals have a single valence electron ns1 that is outside the noble gas core. The loosely held s- electron present in this outermost shell makes these elements electropositive metals.
  
  
• Atomic and ionic radii: The alkali metal atoms are of the largest size in a particular place of the periodic table. They become larger with the increase in atomic number.
  
  
• Ionisation Enthalpy: The ionisation enthalpy of alkali metals is considerably low. It decreases the group from Li to Cs.
  
  
• Hydration Enthalpy: The hydration enthalpies of the alkali metals present in the s- block decrease with the increase in ionic sizes.

Physical properties

• The alkali metals are soft, light, and silvery-white metals.
• They have a low density because of their large sizes.
• Alkali metals’ boiling and melting points are always low, indicating a weak metallic bonding.
• Respective flame tests can detect alkali metals. They can be determined by atomic absorption spectroscopy or flame photometry.

Chemical properties

• Reactivity towards air: Alkali metals tend to tarnish in dry air. That happens due to the formation of their respective oxides, which react with moisture to form hydroxides. Later, they burn vigorously in the oxygen, forming oxides.
• Reactivity towards water: They react with water to form di-hydrogen and hydroxide. The chemical reaction is as follows:

2M + 2H2O → 2 M+ + 2OH- + H2

Here, M refers to the alkali metal.

• Reactivity towards dihydrogen: They also react with dihydrogen to form hydrides at about 673k. All the alkali metal hydrides are also ionic solids. They have high melting points.
  
  
• Reactivity towards halogens: Alkali metals react with halogens to form ionic halides.
  
  
• Reducing nature: They are known to be strong reducing agents. Among them, lithium is the most powerful one, while sodium is the least powerful one.
  
  

• Solutions in liquid ammonia: Alkali metals dissolve in liquid ammonia readily. Thus, they give solutions that are conducted in nature.

Group 2 – Alkaline Earth Metals

Atomic properties

• Electronic configuration: The alkaline earth metals have two electrons in the s orbital of the valence shell. Their general electronic configuration is presented as noble gas or ns2. The compounds of these elements are ionic.
  
  
• Atomic and ionic radii: The atomic and ionic radii of the alkaline earth metals are smaller than that of the alkali metals. That happens due to the increased nuclear charge in the said elements.
  
  
• Ionisation Enthalpy: The alkaline earth metals have elements, including low ionisation enthalpies. That happens because of the relatively larger size of the atoms.
• Hydration Enthalpy: Just like alkali metals, the hydration enthalpies of the alkaline earth metal ions decrease an increase in the ionic size down the group. Their hydration enthalpies are larger than that of the alkali metal ions.

Physical properties

• The alkaline earth metals are white, silvery, lustrous, and relatively soft.
• However, these metals are harder than alkali metals.
• The boiling and melting points of the alkaline earth metals are higher than alkali metals.

Chemical properties

• Reactivity towards air and water: Magnesium and Beryllium are kinetically inert to water and oxygen. That happens because of the formation of an oxide film over each of their surfaces. Moreover, magnesium is more electropositive in nature.
  
  
• Reactivity towards halogens: All alkaline earth metals react with halogens to form hydrides. They combine with halogens at an elevated temperature.
  
  
• Reactivity towards hydrogen: All the alkaline earth metals except beryllium combine with hydrogen to form their respective hydrides.
  
  
• Reactivity towards acids: These metals readily combine with acids to liberate dihydrogen.
  
  
• Reducing nature: Just like alkali metals, alkaline earth metals are also strong reducing agents. Their large negative values indicate the same.
  
  
• Solutions in liquid ammonia: Similar to alkali metals, alkaline earth metals react with liquid ammonia to form a deep blue solution while forming ammoniated ions.

Difference Between s- block and p- block elements

• The s- block elements have their valence electrons in the outermost s orbital. On the other hand, the p- block elements have their valence electrons in the outermost p orbital of the periodic table.
  
  
• The elements of the s- block can have 0, +1, and +2 oxidation states. P- block elements, however, show a varied number of oxidation states ranging from -3, 0, to +5.
  
  

• The s- block elements form both ionic and metallic bonds. In contrast, the p- block elements form covalent or ionic bonds.
  
  
• All the s- block elements are metals. On the other hand, most of the p- block elements are non-metals. The rest of them are metalloids.
  
  
• The electronegativity of the s- block elements is comparatively lesser as compared to the p- block elements.

Conclusion

Both the s- block and p- block elements are found in the periodic table of elements. They are grouped accordingly depending on the position of valence electrons in their respective orbitals. The main difference between the s- block and the p- block elements is the difference in positioning of their respective valence electrons. The above study material notes on block elements (alkali and alkaline earth metals) help us understand their properties better. The s- block consists of two groups, namely the alkali and alkaline earth metals. Both these groups have separate characteristics. They combine with various other elements to form ions, hydrides, and other important chemical properties.