Question

Nitrogen (atomic number $7$) and Phosphorus (atomic number $15$) belong to the group $15$ of the periodic table. Write the electronic configuration of these two elements. Which will be more electronegative? Why?

Answer 1

Hint: Elements belonging to the same group have the same valence electrons or the outermost electronic configuration. Also there are certain trends followed in the series or in the group. Based on these we can answer the above question.

Complete answer:
In the modern periodic table, the physical and chemical properties of the elements are periodic functions of their atomic numbers. Those elements which have similar outer electronic configurations in their atoms are arranged in vertical columns, referred to as groups or families.
In Group $15$ there are five elements, these are $nitrogen,phosphorus,arsenic,antimony,andbismuth$ While writing the electronic configuration we follow the three rules, namely Pauli’s exclusion principle, Hund's rule and Aufbau’s principle. The outer electronic configuration for this group is $n{s}^{2}n{p}^3$ . Let us start with the electronic configuration of the $Nitrogen$ atom, which contains two electrons in each s-orbital and three electrons in p-subshell. It is written as $1s^{2}2s^{2}2p^3$ . For the $phosphorus$ atom which has atomic number $15$ . The electronic configuration is $1s^{2}2s^{2}2p^{6}3s^{2}3p^3$
As mentioned in the hint that there are certain trends observed across or down the group. Electronegativity is such an example. As we can see from the electronic configuration of these two atoms the $Nitrogen$ is smaller in size than the $phosphorus$ element. The size of the $Nitrogen$ is small due to which the attraction of its nucleus for a shared pair of electrons will be more. Also as we move down the group the electronegativity decreases as more and more shells are added to the atom which results in increased distance between the nucleus and the valence electrons reducing the effective nuclear charge.

Note:
Electronegativity is the ability of an atom in a chemical compound to attract a shared pair of electrons. Electronegativity is not a measurable quantity. It is not constant for any given element and varies depending on the element to which it is bound.