Complete the exercises below. a. Using Werner’s definition of valence, which property is the same as oxidation number, primary valence or secondary valence? b. What term do we normally use for the other type of valence? c. Why can NH₃ serve as a ligand but BH₃ cannot?

Verified step by step guidance

1. Step 1: Understand Werner's Coordination Theory. Alfred Werner proposed that metal ions have two types of valences: primary and secondary. The primary valence corresponds to the oxidation state of the metal, while the secondary valence refers to the coordination number, which is the number of ligand atoms bonded to the metal ion.
2. Step 2: Answer part (a). According to Werner's definition, the primary valence is the same as the oxidation number. This is because the primary valence represents the charge on the metal ion, which is equivalent to its oxidation state.
3. Step 3: Answer part (b). The term we normally use for the secondary valence is the 'coordination number.' This refers to the number of ligand atoms that are directly bonded to the central metal ion in a coordination complex.
4. Step 4: Consider the properties of NH₃ and BH₃ as ligands. A ligand is a molecule or ion that can donate a pair of electrons to a metal ion to form a coordinate bond. NH₃ can serve as a ligand because it has a lone pair of electrons on the nitrogen atom that can be donated to a metal ion.
5. Step 5: Explain why BH₃ cannot serve as a ligand. BH₃ does not have a lone pair of electrons available for donation. In BH₃, the boron atom is electron-deficient and forms three covalent bonds with hydrogen, leaving no lone pairs to donate to a metal ion.

Key Concepts

Werner's Theory of Coordination Compounds

Werner's theory distinguishes between primary and secondary valences in coordination compounds. Primary valence corresponds to the oxidation state of the central metal ion, while secondary valence refers to the number of ligands attached to the metal. This framework helps in understanding the bonding and structure of complex ions.

Ligands and Coordination Chemistry

Ligands are molecules or ions that can donate a pair of electrons to a central metal atom to form a coordination complex. The ability of a substance to act as a ligand depends on its electron-donating capacity and steric factors. For example, NH₃ can donate a lone pair of electrons, while BH₃, being electron-deficient, cannot act as a ligand.

Oxidation Number

The oxidation number is a concept used to indicate the degree of oxidation of an atom in a compound. It reflects the number of electrons an atom can gain, lose, or share when forming chemical bonds. In coordination chemistry, the oxidation number of the central metal ion is crucial for determining its reactivity and the overall charge of the complex.