Question

What determines the nucleophile’s strength?

Answer 1

A nucleophile is a kind of chemical species that donate electron pairs to electrophiles. By this sharing and taking up of electrons a chemical bond is formed between them.

Complete step by step answer:
Nucleophiles are electron rich species and hence they can donate electrons to form bonds and therefore, they are also known as Lewis bases.
Nucleophilicity is the nucleophilic character of different nucleophiles. This can also be known as nucleophilic strength.
So, nucleophiles are leaving groups and their relative strength is nucleophilic strength.
It depends on various factors such as polarizability, solvent, charge, basicity, or nature of substitutes.
Nucleophiles can be neutral or negatively charged but it should have electrons to donate. But increasing the negative charge increases nucleophilicity like N in $N{{H}_{2}}$ is a better nucleophile than N in $N{{H}_{3}}$ since it is negatively charged there.
As basicity decreases from left to right in a period so does nucleophilicity. But exceptions are always there like while moving from top to bottom in a group in halogens they do not follow basicity behavior.
Depending upon the type of solvent polar non polar protic aprotic nucleophilicity varies. In aprotic solvents nucleophilicity increases down the group while in aprotic it decreases down the group.
Nucleophilicity increases with increase in atomic size because larger elements diffuse and polarized electron clouds easily.
Nucleophilicity is hindered due to steric hindrance.

Note: We have seen that nucleophilicity is dependent on a lot of factors but at the same time all these factors can vary depending upon the type of nucleophile their chemical composition and structure.