Problem 39 - General Chemistry: Principles and Modern Applications

Question

From each of the following names, you should be able to deduce the formula of the complex ion or coordination compound intended. Yet, these are not the best systematic names that can be written. Replace each name with one that is more acceptable: (a) cupric tetraammine ion; (b) dichlorotetraammine cobaltic chloride; (c) platinic(IV) hexachloride ion; (d) disodium copper tetrachloride; (e) dipotassium antimony(III) pentachloride.

Step-by-Step Solution

Answer

Correct names according to the IUPAC rules are: (a) \([Cu(II)(NH_3)_4]^{2+}\) ion; (b) \([Co(III)(NH_3)_4 Cl_2]Cl\); (c) \([Pt(IV)Cl_6]^{2-}\) ion; (d) \(Na_2[Cu(II)Cl_4]\); (e) \(K_2[Sb(III)Cl_5]\).

Step 1: Understand the Nomenclature Rules

The first step requires an understanding of nomenclature rules. The name of a transition metal ion is written in roman numerals in parentheses to indicate the oxidation number of the metal, followed by the name of the ligand. The ligand name ends with 'o'.

Step 2: Naming cupric tetraammine ion

This complex ion can be expressed as \([Cu(NH_3)_4]^{2+}\). The correct name, following the IUPAC rules, is \([Cu(II)(NH_3)_4]^{2+}\) ion.

Step 3: Naming dichlorotetraammine cobaltic chloride

The molecular formula of this compound is \([Co(NH_3)_4 Cl_2]Cl\). According to IUPAC rules, this would be correctly named as \([Co(III)(NH_3)_4 Cl_2]Cl\).

Step 4: Naming Platinic(IV) hexachloride ion

The formula for this can be given as \([PtCl_6]^{2-}\). According to the rules, the correct name should be \([Pt(IV)Cl_6]^{2-}\) ion.

Step 5: Naming disodium copper tetrachloride

The formula for this compound is \(Na_2[CuCl_4]\). Therefore, the correct IUPAC name is \(Na_2[Cu(II)Cl_4]\).

Step 6: Naming dipotassium antimony(III) pentachloride

The formula for this compound is \(K_2[SbCl_5]\). Therefore, according to the naming rules, the correct name would be \(K_2[Sb(III)Cl_5]\).

Key Concepts

IUPAC Nomenclature

In coordination chemistry, IUPAC nomenclature is essential for naming complex ions and coordination compounds systematically. Understanding these rules helps in accurately conveying the structure and composition of a compound.
A systematic name includes the following components:

• The ligands are named first in alphabetical order, regardless of their charges. Each ligand name ends in 'o'. For example, "ammine" for NH₃ and "chloro" for Cl^-.
• The central metal atom is named after the ligands with its oxidation state indicated in parentheses using Roman numerals, such as 'Iron(III)'.
• If the complex is an anion, the metal's name ends with the suffix '-ate', such as "ferrate" for iron.

Through this method, one can derive meaningful chemical information from a compound's name and systematically name a variety of coordination compounds.

Complex Ions

Complex ions are species formed from a central metal atom or ion bonded to surrounding molecules or anions, known as ligands. The formation of complex ions is common with transition metals due to their ability to accept electrons in vacant d-orbitals.

Ligands are donor molecules that have lone pairs of electrons used to form coordinate covalent bonds with the central atom or ion. This bonding is unique as both shared electrons come from the ligand. Examples include water (H₂O) and ammonia (NH₃).

The overall charge of a complex ion is the sum of the charges on the central metal ion and the ligands. This can be calculated by:

• Assigning oxidation states to the ligands and metal centers.
• Balancing the sum of these charges with the overall charge.

Understanding the structure of complex ions helps in deducing the geometries and properties of coordination compounds.

Oxidation Numbers

The oxidation number is a key concept in chemistry used to describe the degree of oxidation of an atom within a compound. They are typically represented by Roman numerals.

• For transition metals, the oxidation number indicates the number of electrons it has lost or gained.
• These are crucial in determining the naming of coordination compounds, as seen in the IUPAC nomenclature system.

Assigning oxidation numbers involves calculating from known rules:

• The sum of oxidation numbers in a compound must equal the overall charge.
• Oxidation numbers of pure elements are, by definition, zero.
• In complex ions like \( \left[ \text{Co}(\text{NH}_3)_4 \text{Cl}_2\right]^+ \), Co would potentially be assigned +3 based on ligand charges.

Correctly assigning these values is essential for understanding chemical reactivity and nomenclature of the compounds.

Transition Metals

Transition metals are elements found in groups 3-12 in the periodic table. They are uniquely characterized by having partially filled d-orbitals. This property allows them to form various oxidation states and complex ions.
Transition metals are known for:

• High melting and boiling points due to strong metallic bonds.
• Diverse oxidation states, which are essential for forming complex ions and useful in various chemical reactions.
• Forming colored compounds, which often arise from electron transitions between different d-orbitals.

An understanding of transition metals is important when discussing topics like oxidation numbers and the formation of complex ions. Applications of these metals range from catalysis to creating colorful displays in compounds. This makes them crucial for both industrial and scientific fields, influencing everything from material science to bioinorganic chemistry.