Question

Examine the following table of formulas and names. Which of the compounds is/are named correctly? Formula Name a. \(\mathrm{Al}_{2} \mathrm{~S}_{3}\) dialuminum trisulfate \(\begin{array}{ll}\text { b. CuNO }_{3} & \text { copper(III) nitrate }\end{array}\) c. \(\mathrm{Fe}\left(\mathrm{ClO}_{4}\right)_{2} \quad\) iron(III) chiorate \(\begin{array}{ll}\text { d. CsBr } & \text { bromium ceside }\end{array}\) e. \(\mathrm{S}_{2} \mathrm{~F}_{4}\) disulfur tetrafluoride

Short answer

Only compound e) \(\mathrm{S}_{2} \mathrm{~F}_{4}\), named as "disulfur tetrafluoride", is named correctly according to IUPAC naming conventions.

Step-by-step solution

(Step 1: Check option a) \(\mathrm{Al}_{2} \mathrm{~S}_{3}\))

(To name this compound, we consider that it's made of aluminum (Al, a metal) and sulfur (S, a non-metal). When metals and non-metals form compounds, the naming convention is to use the name of the metal followed by the non-metal with an 'ide' suffix. In this case, the correct name should be "aluminum sulfide". The given name, "dialuminum trisulfate", is incorrect.)

(Step 2: Check option b) \(\mathrm{CuNO}_{3}\))

(This compound consists of copper (Cu, a metal) and nitrate (\(\mathrm{NO}_{3}\), a polyatomic ion). Copper is a transition metal, and it can form ions with different charges, so we need to include a Roman numeral representing the charge of the copper ion in the name. In this case, since nitrate has a -1 charge, the copper ion should have a +1 charge to balance the compound. Therefore, the correct name should be "copper(I) nitrate". The given name, "copper(III) nitrate", is incorrect.)

(Step 3: Check option c) \(\mathrm{Fe}\left(\mathrm{ClO}_{4}\right)_{2}\))

(This compound contains iron (Fe, a metal) and perchlorate (\(\mathrm{ClO}_{4}\), a polyatomic ion). Iron is a transition metal, so we need to include a Roman numeral indicating its charge in the name. To balance the -2 charge of the two perchlorate ions, the iron ion should have a +2 charge. So, the correct name should be "iron(II) perchlorate". The given name, "iron(III) chiorate", is incorrect.)

(Step 4: Check option d) \(\mathrm{CsBr}\))

(This compound is formed by cesium (Cs, a metal) and bromine (Br, a non-metal). Following the naming convention, it should be named as "cesium bromide". The given name, "bromium ceside", is incorrect.)

(Step 5: Check option e) \(\mathrm{S}_{2} \mathrm{~F}_{4}\))

(This compound contains non-metals sulfur (S) and fluorine (F). We can use prefixes to indicate the number of atoms present. In this case, the correct name should be "disulfur tetrafluoride". The given name, "disulfur tetrafluoride", is correct.) From the analysis of the given options, only option e) is named correctly.

Key concepts

Inorganic Compound Naming

Understanding how to name inorganic compounds is fundamental for students studying chemistry. It follows specific rules helping to indicate what elements and how many of each are present in a compound. When dealing with a binary inorganic compound (a compound with two different elements), like aluminum sulfide (Al_{2}S_{3}), the metal is named first, followed by the non-metal with an 'ide' suffix. Therefore, 'dialuminum trisulfate' is an incorrect name for Al_{2}S_{3}; the proper name is 'aluminum sulfide'.

For compounds with polyatomic ions like CuNO_{3}, the metal's name (copper in this case) is followed by the name of the polyatomic ion (nitrate). Remember, when naming compounds with a transition metal that can have multiple charges, you must indicate the metal's oxidation state in Roman numerals. Therefore, 'copper(III) nitrate' is incorrect for CuNO_{3} since the correct charge on copper to balance nitrate's -1 charge is +1, making the correct name 'copper(I) nitrate'.

Lastly, with non-metal compounds such as S_{2}F_{4}, prefixes like 'di-' for two atoms and 'tetra-' for four atoms are used. Therefore, the correct name is 'disulfur tetrafluoride' and not 'disulfur quadrifluoride' or any other variation. Understanding these rules is essential in mastering chemical nomenclature, simplifying the process of learning chemistry.

Transition Metals

Transition metals, which are found in the d-block of the periodic table, often have multiple possible oxidation states. This means that they can lose different numbers of electrons when forming compounds, resulting in varying charges. Copper, for example, can exhibit a charge of +1 or +2. Consequently, the charge must be specified when naming compounds containing transition metals, which is done using Roman numerals.

In our exercise, copper(I) nitrate and iron(II) perchlorate exemplify this need. For the compound Fe(ClO_{4})_{2}, since the perchlorate ion has a -1 charge and there are two of them, the iron must have a +2 charge to balance the equation, requiring the name 'iron(II) perchlorate'. Not specifying or incorrectly specifying the oxidation state leads to misunderstandings about the compound's composition. Thus, knowing the precise rules for naming transition metal compounds is crucial for clear and effective communication in chemistry.

Polyatomic Ions

Polyatomic ions are charged entities composed of two or more atoms covalently bonded together. They act as a single unit when forming compounds with other ions. Common polyatomic ions include nitrate (NO_{3}^{-}), sulfate (SO_{4}^{2-}), and perchlorate (ClO_{4}^{-}), to name a few.

The charge of a polyatomic ion is critical when it comes to balancing chemical equations and naming compounds. For example, nitrate has a charge of -1, and since it is paired with a copper(I) ion with a +1 charge, they balance to form a neutral compound, CuNO_{3}. In contrast, perchlorate has a -1 charge, but because it appears twice in Fe(ClO_{4})_{2}, we need an iron ion with a +2 charge for balance, reinforcing the importance of recognizing and understanding polyatomic ions in compound formation. Accurately naming and writing formulas for compounds containing polyatomic ions are instrumental skills in chemistry, facilitating clearer communication and understanding of chemical reactions.