Question

In which of the following pairs is the name incorrect? a. \(\operatorname{SiI}_{4},\) silver iodide b. CoCl_ copper(II) chloride c. \(\mathrm{CaH}_{2}\), hydrocalcinic acid d. \(\mathrm{Zn}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2},\) zinc acetate e. \(\mathrm{PH}_{3},\) phosphoric trihydride

Short answer

The pairs with incorrect names are: a. \(\operatorname{SiI}_{4}\), silver iodide (correct name: Silicon tetraiodide) b. CoCl, copper(II) chloride (correct name: cobalt monochloride) c. \(\mathrm{CaH}_{2}\), hydrocalcinic acid (correct name: calcium hydride) e. \(\mathrm{PH}_{3}\), phosphoric trihydride (correct name: phosphine or phosphorus trihydride)

Step-by-step solution

Review the Naming Conventions

For ionic compounds, follow these guidelines: 1. Name the cation (positive ion) first, followed by the anion (negative ion). 2. If the cation is a metal with more than one possible charge (oxidation state), include a roman numeral in parentheses after the metal name, indicating its charge. 3. For the anion, change the element's name to have an '-ide' ending. For covalent compounds: 1. Name the elements in the order they appear in the formula. 2. Use prefixes to indicate the number of each element: mono-, di-, tri-, tetra-, etc. 3. The second element will have an '-ide' ending. For acids: 1. If the anion contains only two elements (it's a binary anion), use the prefix 'hydro-' and the suffix '-ic' added to the root name of the non-hydrogen element, followed by the word 'acid'. 2. If the anion is a polyatomic ion (contains multiple elements), the suffix changes based on the presence or absence of oxygen and is followed by the word 'acid'. Now, let's examine each option and determine if the naming is correct.

Evaluate Each Option

a. \(\operatorname{SiI}_{4}\), silver iodide Incorrect. \(\operatorname{SiI}_{4}\) is not silver iodide (AgI). It's Silicon tetraiodide, which is a covalently bonded compound. The incorrect element 'silver' was used instead of 'silicon.' b. CoCl, copper(II) chloride Incorrect. CoCl is actually cobalt monochloride, not copper(II) chloride (CuCl2). The wrong element 'copper' was used instead of 'cobalt', and no roman numeral was given for the cobalt ion. c. \(\mathrm{CaH}_{2}\), hydrocalcinic acid Incorrect. \(\mathrm{CaH}_{2}\) is calcium hydride, not hydrocalcinic acid. This is an ionic compound, while the given name suggests an acid. d. \(\mathrm{Zn}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{2}\), zinc acetate Correct. This is an ionic compound with zinc as the cation and acetate as the anion. e. \(\mathrm{PH}_{3}\), phosphoric trihydride Incorrect. \(\mathrm{PH}_{3}\) is phosphine (or phosphorus trihydride) rather than phosphoric trihydride. The naming rules for covalent compounds were not applied correctly. In conclusion, options (a), (b), (c), and (e) have incorrect naming conventions.

Key concepts

Ionic Compounds

Ionic compounds are composed of ions held together by strong electrostatic forces known as ionic bonds. These compounds generally form between metals and nonmetals. The metal loses electrons to become a positively charged cation, while the nonmetal gains electrons to become a negatively charged anion. Here’s how you name these compounds:

• Name the cation first. If this cation has multiple possible charges, denote the charge with a Roman numeral in parentheses.
• Then name the anion, modifying the element suffix to '-ide.'

For example, the compound CaH₂ is named "calcium hydride," where calcium is the cation (with no Roman numeral needed as it has a fixed charge of +2), and hydride is the anion form of hydrogen.

Covalent Compounds

Covalent compounds consist of nonmetal atoms bonded together by sharing electrons, creating molecules. These compounds utilize prefixes to indicate the number of atoms present in each element of the compound. Here’s how to approach naming them:

• Name the elements in the sequence they appear.
• Use prefixes like mono-, di-, tri-, etc., to show the number of atoms for each element.
• The second element’s name ends in '-ide.'

For instance, in SiI₄, the compound is known as "silicon tetraiodide," where "tetra-" denotes that four iodine atoms are attached to one silicon atom.

Acids Naming Conventions

Acids are a specific category of compounds that release hydrogen ions (H⁺) when dissolved in water. The naming of acids is dependent on the anion form:

• For binary anions (single element), the prefix "hydro-" and the suffix "-ic" are used, followed by "acid."
• For polyatomic anions containing oxygen, the suffix changes based on the anion's current form: "-ate" becomes "-ic acid," and "-ite" becomes "-ous acid."

For example, HCl is named "hydrochloric acid," and H₂SO₄ (sulfuric acid) arises from the sulfate ion \\( \text{SO}_4^{2-} \).

Cation and Anion Identification

The identification of cations and anions is crucial for correctly naming chemical compounds. Cations are positively charged ions, typically metals, that have lost electrons. Anions, on the other hand, are negatively charged ions, usually nonmetals, that have gained electrons. Here's how to identify and name them effectively:

• Identify the cation first. Metals in these roles often serve as cations with positive charges.
• Recognize the anion second. Nonmetals assume this role, typically acquiring a negative charge when electrons are gained.
• Apply appropriate suffixes and prefixes based on the compound type, as discussed in previous sections.

For example, in zinc acetate (Zn(C₂H₃O₂)₂), zinc acts as the cation, and acetate is the anion. Recognizing these roles helps in accurately applying naming conventions.