The p-block elements are placed to the right side of the periodic table in groups 13-18. In the atoms of p-block elements, the differentiating electron enters the valence p subshell. Thus, in these elements, the n p subshell is gradually filled.
The general valence shell electronic configuration of these elements is ns2, np1-6
. The electronic configuration of helium is 1s2. Although helium does not have p orbitals, it is a p-block element because it resembles that of other p-block elements of the eighteenth group with respect to their properties. Most p-block elements are non-metals, while the remaining are metals and metalloids.
The study of group fifteen elements:
The elements in group fifteen are nitrogen, phosphorus, arsenic, antimony and bismuth. Nitrogen is the major constituent of the earth’s atmosphere, and accounts for 78 per cent of it by volume. It is the first member of this group, and occurs in free sate as a diatomic gas, N2.
Minerals of nitrogen:
Chile saltpetre & Indian saltpetre.
It is also found as the essential constituent in proteins, amino acids, nucleic acids and enzymes. The next element in the group is phosphorus. It is the 11th most abundant element in the earth’s crust. In combined state, it occurs in the form of minerals as phosphates. EX: Chlorapatite, fluoroapatite and hydroxyapatite are some.
Phosphorus is an essential constituent of plant and animal matter. Phosphate groups are constituents of nucleic acids, that is, DNA and RNA. About 60 per cent of bones and teeth are composed of phosphates. Phosphoproteins are present in egg yolk, bone marrow and milk. The remaining elements of the group, that is, arsenic, antimony and bismuth, mainly occur as sulphides.
EX: Arsenopyrite, stibnite and bismuth glance.
The electronic configuration of group the fifteen elements:
The differentiating electron in these elements enters the n p subshell. Hence, the valence shell electronic configuration of these elements is ns2 np3.These elements have five electrons in their valence shell. Due to the exactly half-filled electronic configuration of the ‘n p’ subshell, the elements of this group are fairly stable.
EX: Dinitrogen is an inert gas under normal conditions.
Trends of some atomic properties:
As we move down the group, the atomic radii and ionic radii increase due to the addition of a new principal energy level in each successive element.
These elements show higher values of ionisation enthalpy as compared to group 14 elements. This is due to their higher nuclear charge, smaller atomic radii and stable half-filled electronic configurations. As we move down the group, the value of ionisation enthalpy decreases. This is due to the gradual increase in the atomic size.
Electro-negativity is the tendency of an atom to attract a shared pair of electrons more towards itself. The electro-negativity decreases gradually on moving down the group due to the corresponding increase in the atomic radii.