Problem 106 - Chemistry The Central Science

Question

Name each of the following oxides. Assuming that the compounds are ionic, what charge is associated with the metallic element in each case? \((\mathbf{a})\) \(\mathrm{NiO},(\mathbf{b}) \mathrm{MnO}_{2},(\mathbf{c}) \mathrm{Cr}_{2} \mathrm{O}_{3}\) \((\mathbf{d}) \mathrm{MoO}_{3}\)

Step-by-Step Solution

Answer

a) Nickel(II) oxide, nickel has a +2 charge b) Manganese(IV) oxide, manganese has a +4 charge c) Chromium(III) oxide, each chromium atom has a +3 charge d) Molybdenum(VI) oxide, molybdenum has a +6 charge

Step 1: Identify the metallic elements and the oxidation state of oxygen in each compound

In all these compounds, oxygen is the non-metal element and has an oxidation state of -2. Now, let's identify the metallic elements in each compound: a) NiO b) MnO₂ c) Cr₂O₃ d) MoO₃

Step 2: Determine the oxidation state of the metallic element in each compound

Using the oxidation state rules and knowing that the sum of oxidation states equals the overall charge on the compound, we can determine the oxidation state of the metallic elements. a) NiO Ni - unknown oxidation state O - (-2) oxidation state Ni + (-2) = 0 Ni = +2 The nickel has a charge of +2 in this compound. b) MnO₂ Mn - unknown oxidation state 2 x O - (-2) x 2 = -4 Mn + (-4) = 0 Mn = +4 The manganese has a charge of +4 in this compound. c) Cr₂O₃ 2 x Cr - 2 x unknown oxidation state 3 x O - (-2) x 3 = -6 2 x Cr + (-6) = 0 2 x Cr = +6 Cr = +3 Each chromium atom has a charge of +3 in this compound. d) MoO₃ Mo - unknown oxidation state 3 x O - (-2) x 3 = -6 Mo + (-6) = 0 Mo = +6 The molybdenum has a charge of +6 in this compound.

Step 3: Name each oxide and list the charge of the metallic element

Now that we have found the charge of the metallic element in each compound, we can name the oxides: a) NiO - Nickel(II) oxide, nickel has a +2 charge b) MnO₂ - Manganese(IV) oxide, manganese has a +4 charge c) Cr₂O₃ - Chromium(III) oxide, each chromium atom has a +3 charge d) MoO₃ - Molybdenum(VI) oxide, molybdenum has a +6 charge

Key Concepts

Oxidation State

When dealing with ionic compounds, the concept of oxidation state helps us understand how electrons are distributed among the atoms. Here, oxygen consistently acts with an oxidation state of \(-2\). This is due to its tendency to gain electrons to fulfill its outer shell.
For the metallic elements, initially, we are unaware of their specific oxidation states. Through calculation, we can determine these states.

• In Nickel(II) oxide (\( ext{NiO}\)), nickel must balance oxygen's \(-2\) charge, resulting in nickel's positive charge of \(+2\).
• In Manganese(IV) oxide (\( ext{MnO}_2\)), the two oxygen atoms total \(-4\), so manganese has a charge of \(+4\).
• In Chromium(III) oxide (\( ext{Cr}_2 ext{O}_3\)), oxygen's total \(-6\) charge is divided between two chromium atoms, giving each a charge of \(+3\).
• Finally, Molybdenum(VI) oxide (\( ext{MoO}_3\)) features three oxygen atoms contributing a \(-6\) total charge, countered by molybdenum's \(+6\) charge.

Understanding oxidation states is vital as it illustrates how metallic elements adjust their electron distribution in chemical compounds.

Metallic Elements

Metallic elements play a crucial role in the formation of ionic compounds. This is due to their tendency to lose electrons, consequently forming positive ions, or cations. This quality differentiates them from non-metals, which tend to gain electrons.
Some common properties of metallic elements include:

• High electrical conductivity
• Shiny appearance
• Malleability, allowing them to be shaped
• Ability to form positive ions easily when reacting

In the context of ionic compounds, the metallic element loses its electrons which are then taken up by the non-metal, oxygen in this scenario, which has an affinity towards gaining electrons. By coming together, they form a stable neutral ionic compound with distinct properties.
Thus, understanding the behavior of metallic elements helps explain why they often form specific oxidation states when in compound form, driven by the need to balance the charge of the overall molecule.

Naming Compounds

Naming ionic compounds requires an understanding of both constituent elements and their respective charges. This systematic approach ensures clarity and consistency when identifying compounds.
For metallic elements:

• The metal's name is listed first, as it forms the positive ion (cation).
• The oxidation state of the metal is specified in Roman numerals within parentheses. This is crucial for metals capable of multiple oxidation states, like transition metals.

Followed by the non-metal:

• The name of the non-metal is derived from the element's root name, adding the suffix "-ide" at the end as seen with oxygen becoming "oxide."

The naming examples from the exercise, such as Nickel(II) oxide or Manganese(IV) oxide, demonstrate the systematic use of such nomenclature. By observing these rules, chemists ensure both the composition and the specific charges of cations within ionic compounds are explicitly conveyed through the compound's name.