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Chapter 23: Problem 21

(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 \(\mathrm{NH}_{3}\) serve as a ligand but \(\mathrm{BH}_{3}\) cannot?

Short Answer

Expert verified
(a) The primary valence corresponds to the oxidation number in Werner's definition. (b) The other type of valence is secondary valence, also known as coordination number. (c) \(\mathrm{NH}_{3}\) can serve as a ligand because it has a lone pair of electrons on the nitrogen atom that can donate to a central metal ion, whereas \(\mathrm{BH}_{3}\) cannot, as it has an empty p-orbital and lacks a lone pair to donate.

Step by step solution

01

Determine the type of valence corresponds to oxidation number

According to Werner's theory, a transition metal complex can have two types of valence: primary valence and secondary valence. Primary valence corresponds to the oxidation number of the central metal atom. It is the number of ions or atoms directly bonded to the metal, exhibiting ionic character.
02

Identify the term for the other type of valence

The other type of valence in Werner's theory is secondary valence, also known as coordination number. Secondary valence corresponds to the number of coordinate covalent bonds formed between the central metal ion and the ligands. This type of valence is responsible for the geometrical structure of the complex.
03

Explain ligand properties of NH3 and BH3

Ammonia \(\mathrm{NH}_{3}\) can act as a ligand because it has a lone pair of electrons on the nitrogen atom that can donate to the central metal ion in a complex, forming a coordinate covalent bond. On the other hand, borane \(\mathrm{BH}_{3}\) cannot act as a ligand because boron has an empty p-orbital instead of a filled orbital with a lone pair that can be donated to a metal ion. Hence, \(\mathrm{BH}_{3}\) does not have the necessary electron donor property to form a coordinate covalent bond with a central metal ion.

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Most popular questions from this chapter

When Alfred Werner was developing the field of coordination chemistry, it was argued by some that the optical activity he observed in the chiral complexes he had prepared was due to the presence of carbon atoms in the molecule. To disprove this argument, Werner synthesized a chiral complex of cobalt that had no carbon atoms in it, and he was able to resolve it into its enantiomers. Design a cobalt(III) complex that would be chiral if it could be synthesized and that contains no carbon atoms. (It may not be possible to synthesize the complex you design, but we will not worry about that for now.)

Which periodic trend is partially responsible for the observation that the maximum oxidation state of the transition-metal elements peaks near groups 7 and \(8 ?(\mathbf{a})\) The number of valence electrons reaches a maximum at group 8. (b) The effective nuclear charge increases on moving left across each period. (c) The radii of the transition-metal elements reach a minimum for group \(8,\) and as the size of the atoms decreases it becomes easier to remove electrons.

Carbon monoxide is toxic because it binds more strongly to the iron in hemoglobin (Hb) than does \(\mathrm{O}_{2}\), as indicated by these approximate standard free-energy changes in blood: $$ \begin{aligned} \mathrm{Hb}+\mathrm{O}_{2} & \longrightarrow \mathrm{HbO}_{2} & \Delta G^{\circ}=-70 \mathrm{~kJ} \\ \mathrm{Hb}+\mathrm{CO} & \longrightarrow \mathrm{HbCO} & \Delta G^{\circ}=-80 \mathrm{~kJ} \end{aligned} $$ Using these data, estimate the equilibrium constant at 298 K for the equilibrium $$ \mathrm{HbO}_{2}+\mathrm{CO} \rightleftharpoons \mathrm{HbCO}+\mathrm{O}_{2} $$

A four-coordinate complex \(\mathrm{MA}_{2} \mathrm{~B}_{2}\) is prepared and found to have two different isomers. Is it possible to determine from this information whether the complex is square planar or tetrahedral? If so, which is it?

For each of the following metals, write the electronic configuration of the atom and its \(3+\) ion: (a) Fe, (b) Mo, (c) Co. Draw the crystal-field energy-level diagram for the \(d\) orbitals of an octahedral complex, and show the placement of the \(d\) electrons for each \(3+\) ion, assuming a weak-field complex. How many unpaired electrons are there in each case?
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