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In the periodic table, on moving from left to right in a period and top to bottom in a group, there are similarities in the properties, or a usual trend in the properties can be seen. The specific pattern in the properties of elements present in the periodic table is known as periodic trends. Usually, the periodic trends include atomic radii, ionic radii, electron affinity, ionisation enthalpy, electronegativity, metallic character, and chemical reactivity. However, some elements show anomalous behaviour to these usual trends due to some specific properties of elements. Properties can be defined in many ways.
The common properties, along with some of the exceptions, can be described below:
Electronic Configuration
The general electronic configuration of p- block elements in ns2 np1-6 (n represents the outermost shell or principal quantum number). The valence electron can be calculated depending on the group number of elements.
Helium is an exception as it has electronic configuration ns2; therefore, it is not a p-block member. However, it is placed in the p-block.
Atomic Radii
On moving from left to right in a period, atomic radii decrease due to an increase in effective nuclear charge.
On moving down the group, the atomic and ionic radii increase as the number of shells increases, and hence atomic radii increase.
Exception: The atomic radii of group 13 elements are smaller than corresponding group 2 elements.
Ionisation Enthalpy
On moving from left to right in a period, ionisation enthalpy increases due to an increase in effective nuclear charge and a decrease in atomic size.
On moving down the group, the atomic and ionic radii decrease as the number of shells increases, and the outermost electron has less attraction towards the nucleus.
Exception: Group 15 and 18 have a deviated trend than usual due to more stability of half-filled orbital and fully filled orbitals.
Covalency
P-block elements show covalent bonding. Covalency decreases on moving from left to right, whereas electrovalency increases. The tendency to form ionic bonding increases from left to right in a period. Usually, halogens form stable ionic compounds as they accept electrons and form anions.
Oxidation State
The maximum oxidation state of a p- block element that it can exhibit is the sum of ns and np electrons (valence shell electrons). On moving from left to right in a period, the oxidation state increases due to an increase in the number of valence electrons. Therefore, the oxidising character increases from left to right in a period.
Exception: Fluorine always has an oxidation state -1 (being the most electronegative element) and noble gases.
Inert Pair Effect
It is the phenomenon in which valence electrons of the s- subshell do not participate in the reactions due to poor shielding of d and f electrons and the necessity of high energy to separate the non-bonding electrons. Due to the inert pair effect, the lower compounds present in particular groups are more stable in lower oxidation states than that of characteristic oxidation states of the group. The s-electrons do not participate in bonding, and hence oxidation states get lowered.
Examples: Group 14- Sn+2 , Pb+2
Group 15- Sb+3 , Bi+3
Metallic Nature
On moving from left to right in a period, the metallic nature decreases. On moving down the group, it increases.
P- block contains all three types of elements-metals, metalloids, and nonmetals. Metalloids and nonmetals are only present in the p-block.
Conclusion
The p-block holds a variety of elements with various common as well as characteristic properties. The various groups present show their individual characteristic properties that are not found in other blocks of the periodic table.
With the help of common periodic trends, one can study the properties of elements and their compounds.
