What are the key factors that influence nucleophilicity?

One factor that influences nucleophilicity is the charge. Nucleophilicity increases as the electron density of an atom increases. The conjugate base is typically a better nucleophile. Another factor is the choice of solvent. Either polar protic or polar aprotic solvents can significantly affect nucleophilicity. In polar protic solvents, nucleophilicity increases going down the periodic table due to decreased ability for hydrogen bonding. In polar aprotic solvents, nucleophilicity correlates with basicity, with fluoride ion being the most reactive. A third factor is steric hindrance. Nucleophilicity decreases with increasing steric hindrance or bulkiness. Bulkier nucleophiles have slower reaction rates and lower nucleophilicity. A fourth factor is electronegativity. Across the periodic table, nucleophilicity increases with decreasing electronegativity. As electronegativity increases, nucleophilicity decreases. This trend applies to atoms in the same row of the periodic table.