Problem 34 - Chemistry in 30 days

Question

Which of the following is a pseudohalogen? (a) \(\mathrm{IF}_{7}\) (b) \((\mathrm{CN})_{2}\) (c) \(\mathrm{ICl}_{2}\) (d) \(\mathrm{I}_{3}^{-}\)

Step-by-Step Solution

Answer

(CN)2 is the pseudohalogen.

Step 1: Define Pseudohalogens

Pseudohalogens are polyatomic molecules that resemble halogens in their chemistry. They often form similar types of compounds and exhibit similar reactivities as halogens.

Step 2: Identify Characteristics of Pseudohalogens

Pseudohalogens usually exist as diatomic or polyatomic molecules, similar to diatomic halogens (e.g., Br extsubscript{2}), and can form anions like pseudohalide ions (e.g., CN extsuperscript{-} which forms (CN) extsubscript{2}).

Step 3: Analyze Each Option

Examine each molecule:- \(\mathrm{IF}_{7}\): An iodine fluoride compound, not diatomic or similar to halogens.- \((\mathrm{CN})_{2}\): A diatomic molecule, forming an anion similar to halogens.- \(\mathrm{ICl}_{2}\): A compound with iodine and chlorine, not forming diatomic molecules or anions like halogens.- \(\mathrm{I}_{3}^{-}\): Triiodide ion, not resembling simple halogens or traditional pseudohalides.

Step 4: Identify the Pseudohalogen

Among the given options, \((\mathrm{CN})_{2}\) is a diatomic molecule similar in behavior and structure to halogens, qualifying it as a pseudohalogen.

Key Concepts

Polyatomic Molecules

Polyatomic molecules are entities composed of more than two atoms bonded together. They can include a variety of atoms, forming diverse molecular structures. For instance,

• Ammonia (NH extsubscript{3}) is a trifecta of nitrogen and hydrogen atoms.
• Methane (CH extsubscript{4}) incorporates carbon and hydrogen.

When we talk about polyatomic molecules in the context of pseudohalogens, it means these molecules have a number of atoms bonded in a way that resembles halogens. Pseudohalogens can form because these molecules exhibit similar chemical behaviors to halogens. Additionally, polyatomic molecules can create ions by losing or gaining electrons, much like atoms from the halogen group. This ion formation is crucial for understanding how pseudohalide ions mimic the functionality of halides.

Halogens

Halogens are a group of elements located in Group 17 of the periodic table. These elements include fluorine, chlorine, bromine, iodine, and astatine. Halogens are known for their high reactivity due to having seven electrons in their outer shell. They seek to obtain one additional electron to achieve a stable electronic configuration by forming compounds such as hydrogen halides (e.g., HCl).
A unique characteristic of halogens is their ability to form diatomic molecules, where two atoms pair to form molecules like Cl extsubscript{2} or Br extsubscript{2}. This property results in vibrant colored gases, corrosive liquids, and pungent solids. Halogens are involved in forming various salts and organic compounds due to their highly reactive nature.
Moreover, their diatomic structure allows them to react in ways that can form complex anionic species, paralleling some behaviors seen in pseudohalogens.

Pseudohalide Ions

Pseudohalide ions are ions that mimic the chemistry of halides (like Cl extsuperscript{-} or Br extsuperscript{-}) in their reactions and ability to form similar compounds. These ions are derived from pseudohalogen molecules. A pseudohalogen behaves like a traditional halogen, yet it is composed of polyatomic rather than monatomic structures.

• An example of a pseudohalide ion is the cyanide ion (CN extsuperscript{-}).
• Here, cyanogen ((CN) extsubscript{2}) is the pseudohalogen because it resembles diatomic halogens.

Pseudohalide ions can pair up to form solid compounds much like halides. Their ability to simulate much of the chemical behavior of halogens makes them particularly interesting for chemists exploring new compound synthesis and reaction pathways. Additionally, their presence underscores the fascinating interplay between structure and chemical function in the broader field of inorganic chemistry.