Question

How does electronegativity change as effective nuclear charge increases?

Answer 1

First approach this question based on the concept of electronegativity and based on the shielding effect of the core electrons. As we know that the phenomenon electronegativity refers to the ability of the atoms to attract the electrons effectively towards itself.

Complete step by step answer:
- It is asked about the trend between the changes in electronegativity if the effective nuclear charge increases.
- To solve the question, the preliminary concept that should be known is about the shielding effect of the electrons and the concept of electronegativity.
Let us first discuss the shielding effect, we know that the electrons are negatively charged and the electrons in the atoms repel each other since they are likely charged and they possess attraction towards the nucleus since the nucleus is positively charged. And we are familiar with the fact that there are various shells present in the atom in which electrons are distributed. The electrons present repels each other and the outer electrons are shielded from the attraction of the nucleus by the core electrons.
- And due to this shielding effect, the outer electrons can be easily removed, since they are loosely bound.
- So we can say that as the inner electrons increase the shielding effect will be more and the outer electrons will have very less affinity to stay with the atom.
- The other part i.e. electronegativity is the tendency of the atoms to attract its electrons towards itself. In that sense the outer electrons must be tightly bound to electrons.
- Now let us connect the two parameters with effective nuclear charge. We know that in a period the shielding effect will be same since the core electrons i.e. the electrons which is nearer to the nucleus will same in number, only the valence electrons and the effective nuclear charge are increasing .The effective nuclear charge is net positive charge experienced by electron in a multi-electron system.
- And now we know that since shielding effect is constant the role of effective nuclear charge only will affect electronegativity parameter in a row i.e. along a period. Since effective nuclear charge increases the electrons will be attracted by the nucleus more effectively. Hence the outer electrons are tightly bound with the atoms i.e. it attracts its electrons more effectively which accounts for electronegativity.
Hence we can conclude that as effective nuclear charge increases the electronegativity of the atom also increases, they are directly proportional to each other.

Note: Along a period we can say that the electronegativity increases from left to right as the effective nuclear charge is increasing left to right.
- But along a group the electronegativity decreases even though effective nuclear charge is increasing, since new shells are introduced, shielding effect and the size of the atoms are increasing down the group.
- Electronegativity of the atom decreases when size of the atom increases.