Question

Write chemical formulas for each of the following: (a) tetrachloroaurate(III) ion (b) bis(ethylenediamine) dinitroiron(III) ion (c) sodium tetraamminedicarbonatocobalt(III) (d) ethylenediaminetetraacetatoferrate(II) ion (e) diamminedichloroplatinum(II)

Short answer

[AuCl4]-, [Fe(en)2(NO2)2]+, Na[Co(NH3)4(CO3)2], [Fe(EDTA)]2-, [Pt(NH3)2Cl2]

Step-by-step solution

Identify the Components of the compound - (a)

Identify the central metal ion, its oxidation state, and the ligands. For tetrachloroaurate(III), gold (Au) is the central metal with an oxidation state of +3, and there are four chloride (Cl) ligands.

Write the Formula - (a)

Combine the central ion with its ligands and indicate the overall charge. Since the oxidation state of gold (Au) is +3 and each chloride ion has a -1 charge, the overall charge of the ion is -1: \[\text{AuCl}_4^{-}\].

Identify the Components of the compound - (b)

Identify the central metal ion, its oxidation state, and the ligands. For bis(ethylenediamine) dinitroiron(III), iron (Fe) is the central metal with an oxidation state of +3, there are two ethylenediamine (en) and two nitro (NO2) ligands.

Write the Formula - (b)

Write the coordination complex with the cationic part first, noting that each ethylenediamine carries no charge and each nitro group carries a -1 charge. Considering iron's +3 charge, the complex will have a positive charge of +1: \[\text{[Fe}(\text{en})_2(\text{NO}_2)_2]^{+}\].

Identify the Components of the compound - (c)

Identify the central metal, its oxidation state, the ligands, and any counter ions. In sodium tetraamminedicarbonatocobalt(III), cobalt (Co) is the central metal with an oxidation state of +3, there are four ammonia (NH3) ligands, two carbonato ligands (CO3), and sodium (Na) as the counter ion.

Write the Formula - (c)

The complex will have an overall charge of +1, which is balanced by one sodium ion. The formula is: \[\text{Na}[\text{Co}(\text{NH}_3)_4(\text{CO}_3)_2]\].

Identify the Components of the compound - (d)

Identify the central metal ion and the ligands. For ethylenediaminetetraacetatoferrate(II), iron (Fe) is the central ion with a +2 oxidation state, and there is one ethylenediaminetetraacetate (EDTA) ligand which has a -4 charge.

Write the Formula - (d)

The formula of the complex ion is \[\text{[Fe}(\text{EDTA})]^{2-}\] since the charge of EDTA balances the charge on iron.

Identify the Components of the compound - (e)

Identify the central metal ion and the ligands. Diamminedichloroplatinum(II) contains platinum (Pt) as the central ion with a +2 oxidation state, and there are two ammonia (NH3) and two chlorine (Cl) ligands present.

Write the Formula - (e)

The formula can be written as \[\text{[Pt}(\text{NH}_3)_2\text{Cl}_2\] considering the oxidation state of platinum and the number of each type of ligand.

Key concepts

Coordination Chemistry

Coordination chemistry is a branch of inorganic chemistry that deals specifically with coordination compounds. These compounds consist of a central metal ion surrounded by molecules or ions known as ligands. For example, the tetrachloroaurate(III) ion includes a gold (Au) ion as the central atom and chloride ions acting as ligands.
Ligands are crucial because they can alter the properties of the metal ion, including its color, reactivity, and solubility. In our given exercise, different ligands such as chlorine, ethylenediamine, and nitro groups are bound to central metal ions to form various coordination complexes. Understanding the arrangement of these components is essential for writing the correct chemical formulas of coordination compounds, as we see in the solutions presented.

Oxidation States

In coordination compounds, oxidation states indicate the degree of oxidation of the central metal atom. It is commonly represented by a Roman numeral and can be determined by adding up the charges of the ligands and any counter ions present. The overall charge of a complex must balance out when combining the charge of the central metal and its surrounding ligands.For example, in bis(ethylenediamine) dinitroiron(III), the iron (Fe) has an oxidation state of +3. This oxidation state influences the charge of the entire complex and how ligands are arranged around the metal ion. Correctly identifying oxidation states is not just a bookkeeping detail; it is crucial for predicting reactivity and stability of coordination complexes, which is why it is a key step in the exercise provided.

Ligands in Coordination Complexes

Ligands are atoms, ions, or molecules that can donate a pair of electrons to a central metal ion to form a coordination bond. They are what give coordination compounds their unique properties and are as crucial as the central metal itself. Ligands can be simple ions like chloride in the tetrachloroaurate(III) ion, or more complex molecules such as ethylenediaminetetraacetate (EDTA) in the ethylenediaminetetraacetatoferrate(II) ion.Ligands can vary greatly in their properties. For instance, ammonia (NH3), a neutral molecule, acts as a ligand in the sodium tetraamminedicarbonatocobalt(III) complex. The type and number of ligands, combined with their charge, significantly influence the geometry and the overall charge of the coordination complex, which can be seen through the variety of examples in the exercise.