Question

What is wrong with the name (given in parentheses or brackets) for each of the following compounds: (a) \(\mathrm{BaCl}_{2}\) (barium dichloride), (b) \(\mathrm{Fe}_{2} \mathrm{O}_{3}\) [iron(II) oxide], (c) \(\mathrm{CsNO}_{2}\) (cesium nitrate), (d) \(\mathrm{Mg}\left(\mathrm{HCO}_{3}\right)_{2}\) [magnesium(II) bicarbonate]?

Short answer

Incorrect prefixes and oxidation numbers are used; correct names are: (a) barium chloride, (b) iron(III) oxide, (c) cesium nitrite, (d) magnesium bicarbonate.

Step-by-step solution

Analyze Compound (a)

The given compound is \( \mathrm{BaCl}_{2} \). The name provided is 'barium dichloride'. The error lies in the use of the prefix 'di-' with chloride ions in an ionic compound. Ba is a group 2 element and forms \( \mathrm{Ba}^{2+} \); hence, the compound should be simply named 'barium chloride', without the prefix.

Analyze Compound (b)

The given compound is \( \mathrm{Fe}_{2}\mathrm{O}_{3} \). The name given is 'iron(II) oxide'. Since iron forms both Fe2+ and Fe3+ ions, and the compound has Fe2O3, this indicates iron is in the +3 oxidation state. Therefore, it should be named 'iron(III) oxide', not 'iron(II) oxide'.

Analyze Compound (c)

The given compound is \( \mathrm{CsNO}_{2} \). The name 'cesium nitrate' is incorrect because \( \mathrm{NO}_{2}^{-} \) is the nitrite ion, not the nitrate ion \( \mathrm{NO}_{3}^{-} \). The correct name should be 'cesium nitrite'.

Analyze Compound (d)

The given compound is \( \mathrm{Mg}\left(\mathrm{HCO}_{3}\right)_{2} \). The name 'magnesium(II) bicarbonate' is incorrect because magnesium has a fixed oxidation state of +2 and does not require specification in its name. The correct name is simply 'magnesium bicarbonate'.

Key concepts

Chemical Nomenclature

Chemical nomenclature is the systematic method of naming chemical compounds and is essential for ensuring clear communication in chemistry. Each chemical compound has a unique name that follows specific rules. For ionic compounds, such as those in the exercise, the metal cation is named first, followed by the anion. The metal name is unchanged, while the anion's name often ends in '-ide,' or is based on the polyatomic ion's name.

It's crucial to follow the correct rules, for instance:

• For simple binaries, use the cation name followed by anion, e.g., sodium chloride (NaCl).
• Prefixes like 'di-' should not be used for simple ion counts in ionic compounds.
• If a metal can have multiple charges, the charge is specified in Roman numerals in parentheses, as in iron(III) oxide for Fe2O3.
• Some names may carry historical names retained through conventional use (e.g., water, for H2O).

Understanding chemical nomenclature allows for recognizing errors, such as the unnecessary use of prefixes or incorrect Roman numeral oxidation states, as demonstrated in the examples.

Oxidation States

An oxidation state, also known as an oxidation number, indicates the degree of oxidation of an element in a compound. It reflects the electron control or sharing an atom of an element has in a compound. This concept is key to identifying how ions form and are named. In ionic compounds, metals usually have positive oxidation states, while nonmetals have negative oxidation states due to gaining and losing electrons.

For transition metals like iron, which can form more than one ion, indicating the oxidation state avoids ambiguity. For example:

• Iron can exist as Fe2+ or Fe3+, representing iron(II) or iron(III), respectively.
• Correct identification of oxidation states aids in writing balanced chemical equations and naming ions properly.

It's important to remember that some metals, such as those in group 1 or 2 like barium or magnesium, have fixed oxidation states, simplifying their names without the need for specifying charges.

Ionic Bonds

Ionic bonds form through the transfer of electrons from one atom to another, resulting in the formation of charged ions. This type of bond typically occurs between metals and nonmetals. Understanding ionic bonds helps explain the formation and stability of ionic compounds.

There are fundamental aspects to remember:

• Metal atoms lose electrons to form positively charged cations.
• Nonmetal atoms gain electrons to form negatively charged anions.
• The electrostatic force of attraction between oppositely charged ions forms the ionic bond.
• Ionic compounds generally have high melting and boiling points due to the strength of these bonds.

Recognizing the nature of ionic bonds helps to understand the composition and properties of compounds like barium chloride (BaCl2), where barium and chlorine form stable ionic bonds.

Inorganic Chemistry

Inorganic chemistry focuses on compounds not covered by organic chemistry (not involving primarily carbon-hydrogen bonds). This branch of chemistry studies compounds like salts, metals, and minerals. Ionic compounds, highlighted in the exercise, are a major focus of inorganic chemistry.

Key points about inorganic chemistry include:

• It deals with the behavior and properties of inorganic compounds.
• Inorganic compounds include metals and nonmetals, often forming ionic bonds.
• Understanding periodic table trends and electron configurations is crucial for predicting compound formation.
• This field underpins applications like catalysis, materials science, and environmental chemistry.

Grasping the fundamentals of inorganic chemistry aids in appreciating the nature and naming of ionic compounds such as Fe2O3 (iron(III) oxide) and Mg(HCO3)2 (magnesium bicarbonate), which resulted from particular interactions between elements.