Question

Write the formula for each complex ion or coordination compound. \begin{equation}\begin{array}{l}{\text { a. hexaaquanickel(II) chloride }} \\\ {\text { b. pentacarbonylchloromanganese(I) }} \\ {\text { c. ammonium diaquatetrabromovanadate(III) }} \\ {\text { d. tris(ethylenediamine) cobalt(III) trioxalatoferrate(III) }}\end{array}\end{equation}

Short answer

[Ni(H_2O)_6]Cl_2, Mn(CO)_5Cl, (NH_4)_2[VBr_4(H_2O)_2], [Co(ethylenediamine)_3][Fe(C_2O_4)_3]

Step-by-step solution

Identify the Ligands and Central Metal

First, recognize the ligands and the metal in each complex. For example, hexaaqua indicates six water molecules as ligands and nickel(II) as the metal with a +2 charge.

Write the Chemical Formula for Each Complex

Using the charge and number of ligands, write down the metal symbol with its oxidation state followed by the ligand symbols in parentheses with a subscript indicating how many of them are present. Anions outside the complex should be written last.

Apply Naming Conventions for Charges

If the charge of the complex is nonzero, balance it with counter ions. Cationic complexes will have their counter ions written after the complex, while anionic complexes will have their counter ions placed before the complex ion.

Key concepts

Ligands Identification

Understanding the role of ligands is crucial when writing chemical formulas for coordination compounds. Ligands are molecules or ions that donate at least one pair of electrons to a central metal atom or ion, forming a coordination bond. In the given exercise, the ligands are identified by their specific prefixes and names, such as 'hexaaqua' referring to six water molecules (H_2O)) and 'pentacarbonyl' suggesting five carbonyl (CO)) groups.

When writing a formula, the number of ligands is denoted as a subscript after the ligand's abbreviation. For instance, hexaaqua signifies that you need to write (H_2O)_6) after the metal ion. It's essential to know the common names and abbreviations for ligands to precisely construct the chemical formula for complex ions. Some typical ligand abbreviations include (NH_3) for ammine, (H_2O) for aqua, CO for carbonyl, and (C_2O_4^{2-}) for oxalate.

Coordination Compounds

Coordination compounds consist of a central metal ion bonded to one or more ligands. These compounds are distinctive due to their complex nature and the variety of structures they can form. A correct representation of a coordination compound involves the central metal ion's symbol and oxidation state, followed by the ligands aligned in a specific order, often alphabetical.

In our exercise, compounds like ammonium diaquatetrabromovanadate(III) include both a complex ion and a counter ion. The coordination compound's formula is structured with the metal ion, vanadium (V), followed by its oxidation state (III) denoted in Roman numerals, and the series of ligands and their quantities encapsulated within square brackets [...]. It's essential to acknowledge that complex ions can either be cationic, anionic, or neutral, and this affects the placement of counter ions in the formula.

Oxidation States

Every element in a chemical formula, especially in coordination chemistry, can have an oxidation state that indicates the total number of electrons it has gained or lost. In coordination compounds, identifying the oxidation state of the central metal ion is necessary because it determines the overall charge of the complex and how it bonds with the ligands.

For example, in hexaaquanickel(II) chloride, the (II) indicates that nickel is in a +2 oxidation state. This oxidation number helps us balance the charges when writing the formula. If the sum of charges from the central metal ion and ligands does not equal zero, counter ions are added to equalize the charge, a concept known as charge neutrality. In solutions, step 3 describes this process, which requires counter ions to be written before the complex ion if it is an anionic complex, or after if it is a cationic complex.