The Soft Character of the Central Metal Ion

Soft and hard are two terms used to describe the chemical properties of metal ions. The HSAB principle, which stands for Hard and Soft Acids and Bases, explains that hard acids and bases prefer to react with each other, while soft acids and bases prefer to react with each other. Here is the correct order of the soft character of the central metal ion:

1. Mercury (Hg)

Mercury is a soft metal and has a low electronegativity. It can easily donate electrons to soft bases, making it a soft acid. It can also accept electrons from soft bases, making it a soft base.

2. Gold (Au)

Gold is also a soft metal and has a low electronegativity. It can easily donate electrons to soft bases, making it a soft acid. However, it is less likely to accept electrons from soft bases than mercury.

3. Silver (Ag)

Silver is a borderline metal and can be classified as either hard or soft. However, it is generally considered a soft metal due to its low electronegativity. It can donate electrons to soft bases, but it is not as soft as mercury or gold.

4. Copper (Cu)

Copper is a hard metal and has a high electronegativity. It is not a good donor of electrons to soft bases, making it a hard acid. It can accept electrons from hard bases, making it a hard base.

5. Iron (Fe)

Iron is also a hard metal and has a high electronegativity. It is not a good donor of electrons to soft bases, making it a hard acid. It can accept electrons from hard bases, making it a hard base.

Conclusion

The correct order of the soft character of the central metal ion is mercury > gold > silver > copper > iron. The softness of the metal ion determines its reactivity with soft or hard bases. Soft metal ions are more likely to react with soft bases, while hard metal ions are more likely to react with hard bases.