Question

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

Short answer

(a) \(\mathrm{NiO}\): Nickel(II) Oxide with charge +2. (b) \(\mathrm{MnO}_2\): Manganese(IV) Oxide with charge +4. (c) \(\mathrm{Cr}_2\mathrm{O}_3\): Chromium(III) Oxide with charge +3. (d) \(\mathrm{MoO}_3\): Molybdenum(VI) Oxide with charge +6.

Step-by-step solution

Identifying Elements and Their Charges

Firstly, we'll identify the metal and non-metal elements in each compound and look up their group number (or periodic table column number) to determine how many valence electrons they have: (a) \(\mathrm{NiO}\): Ni (Nickel) is a metal and O (Oxygen) is a non-metal element. (b) \(\mathrm{MnO}_2\): Mn (Manganese) is a metal and O (Oxygen) is a non-metal element. (c) \(\mathrm{Cr}_2\mathrm{O}_3\): Cr (Chromium) is a metal and O (Oxygen) is a non-metal element. (d) \(\mathrm{MoO}_3\): Mo (Molybdenum) is a metal and O (Oxygen) is a non-metal element. Next, we know that Oxygen has 6 valence electrons and wants to gain 2 more to have a full outer shell. Therefore, it will have an oxidation state of -2. Now, we can determine the oxidation states of the metal elements.

Determine the Oxidation States of the Metallic Elements

We'll determine the oxidation states by balancing the charges in each compound: (a) \(\mathrm{NiO}\): Nickel (Ni) is paired with one oxygen (-2 charge). Therefore, the oxidation state of Ni must be +2 to balance the charges. (b) \(\mathrm{MnO}_2\): Manganese (Mn) is paired with two oxygens (2 x -2 = -4 charge). The oxidation state of Mn must be +4 to balance the charges. (c) \(\mathrm{Cr}_2\mathrm{O}_3\): Two chromiums (Cr) are paired with three oxygens (3 x -2 = -6 charge). The 2 chromiums must have a total charge of +6, so each Cr will have an oxidation state of +3. (d) \(\mathrm{MoO}_3\): Molybdenum (Mo) is paired with three oxygens (3 x -2 = -6 charge). The oxidation state of Mo must be +6 to balance the charges.

Name the Ionic Compounds

Using the determined oxidation states, we can now name each ionic compound: (a) \(\mathrm{NiO}\): Nickel(II) Oxide (b) \(\mathrm{MnO}_2\): Manganese(IV) Oxide (c) \(\mathrm{Cr}_2\mathrm{O}_3\): Chromium(III) Oxide (d) \(\mathrm{MoO}_3\): Molybdenum(VI) Oxide. In summary: (a) Nickel(II) Oxide with charge +2. (b) Manganese(IV) Oxide with charge +4. (c) Chromium(III) Oxide with charge +3. (d) Molybdenum(VI) Oxide with charge +6.

Key concepts

Oxidation States

Understanding oxidation states is key to mastering the naming of ionic compounds. An oxidation state, also known as oxidation number, is a figure that represents the total number of electrons an atom either gains or loses to form a chemical bond. When it comes to ionic compounds, which consist of metal and non-metal elements, identifying the oxidation state of the metal can determine how we name the compound.

For instance, oxygen usually has an oxidation state of -2 because it prefers to gain two electrons to fill its outermost electron shell. Metals, on the other hand, tend to lose electrons and thus have positive oxidation states. By balancing the positive charge of the metal with the negative charge of non-metals like oxygen, we can determine the exact oxidation state of the metal. The oxidation state helps us to communicate the precise composition of the compound, such as Nickel(II) indicating that nickel has an oxidation state of +2.

Ionic Charge

Ionic charge refers to the electrical charge that an ion carries. Ions are atoms or molecules that have lost or gained one or more electrons, becoming charged particles. In an ionic compound, the total positive charge of the metal cations (positively charged ions) must balance with the total negative charge of the non-metal anions (negatively charged ions).

Each element has a tendency to either lose or gain electrons to achieve a stable electron configuration, typically that of the nearest noble gas. For example, in Nickel(II) Oxide, the Nickel ion has a +2 ionic charge because it loses two electrons, whereas the Oxygen atom forms an O^2- ion by gaining two electrons. The charges balance out in the ionic compound, making it electrically neutral.

Metal and Non-Metal Elements

Ionic compounds are typically formed between metal and non-metal elements. Metals, found on the left side of the periodic table, are elements that readily lose electrons to become cations. Non-metals, on the right side of the periodic table, gain electrons to become anions.

An essential part of understanding ionic compounds is identifying which element in the formula is the metal and which is the non-metal. This can be done using the periodic table or by memorizing common metals and non-metals. For example, Nickel (Ni), Manganese (Mn), Chromium (Cr), and Molybdenum (Mo) are metals that lose electrons and thus have positive oxidation states in the given compounds. Oxygen (O), on the other hand, is a non-metal and almost always has a -2 oxidation state in these compounds.

Chemical Nomenclature

Chemical nomenclature is the system used for naming chemical compounds. The rules of nomenclature ensure that each compound has a unique and standardized name. For ionic compounds, naming involves combining the name of the metal with that of the non-metal and including Roman numerals to indicate the metal's oxidation state if it is capable of multiple valencies.

The name of the metal is written first, followed by the name of the non-metal with an '-ide' suffix. For instance, the compound MnO2 is called Manganese(IV) Oxide, reflecting the +4 oxidation state of Manganese. It is crucial to know the common oxidation states and ionic charges of elements to name compounds accurately. This systematic approach aids in clear communication among scientists and learners alike.