Which species are more likely to act as ligands? (a) Positively charged ions or negatively charged ions? (b) Neutral molecules that are polar or those that are nonpolar?

A ligand is an ion or molecule that binds to a central metal atom to form a complex molecule or coordination complex. Ligands usually have one or more unshared pairs of electrons that can form a coordinate covalent bond with the metal atom. We can use this definition to examine the properties of the given species and determine which are more likely to act as ligands.

In general, negatively charged ions are more likely to act as ligands than positively charged ions. This is because negatively charged ions, called anions, have additional electrons which they can use to create coordinate covalent bonds with the central metal atom. Conversely, positively charged ions, called cations, have a deficiency of electrons and are less likely to form such bonds. Therefore, negatively charged ions are more likely to act as ligands.

Neutral molecules can also act as ligands if they possess unshared electron pairs that can form coordinate covalent bonds with the metal atom. In general, polar molecules are more likely to act as ligands than nonpolar molecules, as they have regions of positive and negative charge due to differences in electronegativity between their constituent atoms. This charge asymmetry facilitates the formation of coordinate covalent bonds between the polar molecule and the metal atom. In contrast, nonpolar molecules do not possess charge asymmetry, making it less likely for them to form coordinate covalent bonds. Therefore, polar neutral molecules are more likely to act as ligands. To summarize: (a) Negatively charged ions are more likely to act as ligands compared to positively charged ions. (b) Neutral polar molecules are more likely to act as ligands compared to nonpolar molecules.