# The P Block Elements

## Chemistry

### NCERT

1   Discuss the general characteristics of Group $15$ elements with reference to their electronic configuration, oxidation state, atomic size, ionization and electronegativity.

##### Solution :

General trends in group $15$ elements (i) Electronic configuration: All the elements in group $15$ have $5$ valence electrons. Their general electronic configuration is $ns^2 \ np^3$.$\\$ (ii) Oxidation states: All these elements have $5$ valence electrons and require three more electrons to complete their octets. However, gaining electrons is very difficult as the nucleus will have to attract three more electrons. This can take place only with nitrogen as it is the smallest in size and the distance between the nucleus and the valence shell is relatively small. The remaining elements of this group show a formal oxidation state of $-3$ in their covalent compounds. In addition to the $-3$ state, $N$ and $P$ also show $-1$ and $-2$ oxidation states. All the elements present in this group show $+3$ and $+5$ oxidation states. However, the stability of $+5$ oxidation state decreases down a group, whereas the stability of $+3$ oxidation state increases. This happens because of the inert pair effect.$\\$ (iii) Ionization energy and electronegativity: First ionization decreases on moving down a group. This is because of increasing atomic sizes. As we move down a group, electronegativity decreases, owing to an increase in size.$\\$ (iv) Atomic size: On moving down a group, the atomic size increases. This increase in the atomic size is attributed to an increase in the number of shells.

2   Why does the reactivity of nitrogen differ from phosphorus?

##### Solution :

Nitrogen is chemically less reactive. This is because of the high stability of its molecule, $N_2$ . In $N_2$ , the two nitrogen atoms form a triple bond. This triple bond has very high bond strength, which is very difficult to break, It is because of nitrogen’s small size that it is able to form $p \pi - p \pi$ bonds with itself. This property is not exhibited by atoms such as phosphorus. Thus, phosphorus is more reactive than nitrogen.

3   Discuss the trends in chemical reactivity of group $15$ elements.