Problem 103 - Chemistry Matter and Change

Question

Cobalt, a transition metal, forms both the \(\mathrm{Co}^{2+}\) and \(\mathrm{Co}^{3+}\) ions. Write the correct formulas, and give the name for the oxides formed by the two different ions.

Step-by-Step Solution

Answer

- CoO is cobalt(II) oxide - Co₂O₃ is cobalt(III) oxide

Step 1: Understanding Cobalt Ions

Cobalt can form two different ions: - The cobalt(II) ion, \(\mathrm{Co}^{2+}\), which has a charge of +2.- The cobalt(III) ion, \(\mathrm{Co}^{3+}\), which has a charge of +3.

Step 2: Forming the Oxide with Co(II)

To form an oxide from the cobalt(II) ion, we pair \( \mathrm{Co}^{2+} \) with oxygen, which typically forms \( \mathrm{O}^{2-} \) ions. The formula for the oxide is \[ \mathrm{CoO} \], following the requirement for charge balance (each ion contributes 2 charges, one positive and one negative).

Step 3: Naming the Cobalt(II) Oxide

The name for the oxide with cobalt(II) is *cobalt(II) oxide* to indicate the +2 oxidation state of the cobalt ion in the compound.

Step 4: Forming the Oxide with Co(III)

For the oxide of cobalt(III) ion, pair \( \mathrm{Co}^{3+} \) with \( \mathrm{O}^{2-} \). A 2:3 ratio is required to balance the charges, resulting in the formula \[ \mathrm{Co_2O_3} \] because two \( \mathrm{Co}^{3+} \) ions (total +6) will balance with three \( \mathrm{O}^{2-} \) ions (total -6).

Step 5: Naming the Cobalt(III) Oxide

The name for the oxide with cobalt(III) is *cobalt(III) oxide* to indicate the +3 oxidation state of the cobalt ion in the compound.

Key Concepts

Transition Metals

Transition metals are a fascinating group of elements that are located in the d-block of the periodic table. These metals, like cobalt, are unique because they have partially filled d orbitals. This gives them several interesting properties.

• **Variable Oxidation States**: Unlike many other elements, transition metals can form ions with different charges, known as oxidation states. This occurs because electrons can be removed from both the s and d orbitals.
• **Formation of Colored Compounds**: Many transition metals form colorful compounds. This is because of the d-d electron transitions within their d orbitals.
• **Magnetic Properties**: Some transition metals and their compounds are magnetic due to the presence of unpaired electrons.
• **Catalytic Abilities**: These metals are often used as catalysts because they can change oxidation states easily, allowing them to facilitate many chemical reactions.

Cobalt is a classic example of a transition metal, displaying several of these properties. It forms compounds in multiple oxidation states, such as +2 and +3, making it a versatile element in chemistry.

Oxidation States

The term "oxidation state" refers to the hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic. In simpler terms, it's a way of keeping track of electrons during a chemical reaction.

• **Oxidation State Notation**: We write the oxidation state as a Roman numeral in parentheses after the element's name, for example, Cobalt(II) or Cobalt(III).
• **Significance of Oxidation States**: Different oxidation states can result in different chemical and physical properties. This explains why cobalt can form more than one type of oxide.
• **Charge Balance**: In forming ionic compounds, the total positive charge must balance the total negative charge. This principle is crucial when writing chemical formulas using oxidation states.

By understanding oxidation states, students learn how to predict and write chemical formulas, such as CoO for cobalt(II) oxide and Co₂O₃ for cobalt(III) oxide.

Ionic Compounds

Ionic compounds are formed when metals and non-metals transfer electrons to achieve a stable electronic configuration. Transition metals like cobalt form ionic compounds with non-metals, such as oxygen.

• **Ionic Bond Formation**: Ionic bonds form when a metal loses electrons to become positively charged, while a non-metal gains those electrons to become negatively charged.
• **Lattice Structure**: Ionic compounds typically form a crystalline lattice structure, providing stability and high melting points.
• **Charge Balance in Ionic Compounds**: It is essential for the total positive charge to balance the total negative charge for an ionic compound to be stable. For instance, in CoO, both cobalt and oxygen offer two charges, balancing out.

These characteristics are reflected in cobalt oxides where cobalt(II) forms CoO and cobalt(III) forms Co₂O₃.

IUPAC Nomenclature

IUPAC Nomenclature provides a systematic way to name chemical compounds, ensuring that each name is unique and descriptive of the compound's structure.

• **Systematic Naming**: The official name includes the oxidation state of the metal, written in Roman numerals in parentheses. For example, 'cobalt(II) oxide' indicates CoO, while 'cobalt(III) oxide' indicates Co₂O₃.
• **Importance of Nomenclature**: By using IUPAC nomenclature, chemists around the world can clearly communicate the specific compounds they are discussing without ambiguity.
• **Format of Names**: Typically, the metal's name is followed by its oxidation state in Roman numerals, and then the non-metal, often ending in '-ide'.

Understanding IUPAC nomenclature helps simplify the study of chemistry by standardizing how we describe different compounds, leading to clearer communication across scientific communities.