Group I and Group II Elements: Alkali and Alkaline

The groups IA and IIA are placed at the extreme left corner of the periodic table. The elements of these two groups belong to the S block as the differentiating electron enters the S orbital in all these elements. As the S-orbital can accommodate only two electrons, these two groups (IA & IIA) belong to the S-block of the Periodic table. The elements of these two groups have a strong metallic nature.

IA Group Elements or Alkali Metals

The Group IA of the long form of the periodic table consists of six elements, lithium, sodium, potassium, rubidium, cesium and francium. The general electronic configuration of all these elements is ns1. As all these elements are having one electron in the valence shell they are placed in the IA group.

 All these elements are collectively called as alkali metals as the hydroxides of these metals are soluble in water and these solutions are highly alkaline in nature. 

Among all the elements in this group, Lithium shows some abnormal properties. However, lithium resembles magnesium present in the IIA group. This resemblance is due to diagonal relationship. The only radioactive element in this group is francium. It is highly radioactive with a very small half-life period of 21 minutes.

Physical Properties

Electronic Configuration:

All the alkali metals have one valence electron in their outermost shell. They readily lose electron and give monovalent M+ ions. They are not found in the free state in nature as they are highly reactive.

Atomic and Ionic Radii:

In every period the alkali metal atoms have the largest size in the periodic table. The monovalent ion is smaller than the parent atom. On moving down the group as a new shell is added, the atomic radius increases.

Ionization Energy:

Because of their large size, the alkali metals’ ionization energies are very much reduced and therefore the values slowly go lower in the group from Li to Cs. This is because the effect of increasing size decreases the nuclear pull over the outer most electron.

Melting Points and Boiling Points:

Alkali metals have low melting points and the values of melting points decrease gradually down the group. Due to their larger atomic size, the binding energies of their atoms within the crystal lattice are reduced being the cause therefore of a low melting point. Further on moving down the group, their atomic size increases, and the strength of metallic bond decreases which causes decrease in melting points. 

IIA Group Elements Or Alkaline Earth Metals

The Group IIA of the long form of the periodic table consists of six elements, beryllium, magnesium, calcium, strontium, barium and radium. The general electronic configuration of all these elements is ns2. As all these elements are having two electrons in the valence shell they are placed in the IIA group.

The oxides and hydroxides of these elements are alkaline in nature and are available in the earth’s crust. So, these elements are also known as ‘Alkaline Earth Metals’. Among these elements, Radium is radio active.

Electronic configuration:

There are two electrons in the valence shell of these elements. Their general electronic configuration may be represented as ns2 where ‘n’ is the number of the orbit. The compounds of these elements are ionic.

Atomic and Ionic Radii:

The atomic and ionic radii of the alkaline earth metals are smaller than those of the corresponding IA group metals, but larger than the remaining group elements. The size of atom increases gradually from Be to Ra due to the increase in the number of shells. Their ions are large and size of the ions increases from Be2+ to Ra2+

Melting Points and Boiling Points

The melting points and boiling points of alkaline earth metals are higher than those of alkali metals.But regular gradation is not observed.