Question

Given below are the elements and the type of hydrides formed by them. Mark the incorrect match. (a) Phosphorus-Molecular hydride (b) Potassium-Ionic hydride (c) Vanadium-Interstitial hydride (d) Nitrogen-Electron-deficient covalent hydride

Short answer

The incorrect match is (d) Nitrogen-Electron-deficient covalent hydride, as nitrogen typically forms molecular covalent hydrides, not electron-deficient ones.

Step-by-step solution

Understanding Hydride Types

Know that hydrides are classified based on their bonding and electronic characteristics into three types: ionic hydrides, formed with alkali or alkaline earth metals; covalent or molecular hydrides, formed with nonmetals; and metallic or interstitial hydrides, formed with d-block and f-block elements.

Analyzing the Given Matches

Take each element and categorize it based on its position in the periodic table and the usual type of hydride it forms: (a) Phosphorus, a nonmetal, forms molecular hydrides. (b) Potassium, an alkali metal, forms ionic hydrides. (c) Vanadium, a transition metal, can potentially form interstitial hydrides. (d) Nitrogen, a nonmetal, forms covalent hydrides, typically not electron-deficient.

Identifying the Incorrect Match

All categories match the expected hydride type except (d) Nitrogen, which typically forms covalent or molecular hydrides that are not electron-deficient. Typically, electron-deficient hydrides are associated with B-group elements like boron.

Key concepts

Ionic Hydrides

Ionic hydrides are compounds that consist of hydrogen ions (H-) and cations of electropositive metals, typically from the alkali metals (like lithium and sodium) or alkaline earth metals (like calcium and magnesium).

This type of hydride is characterized by ionic bonding between the metal cations and hydride anions, forming a crystalline salt-like structure. They are often used as strong bases and reducing agents in chemical reactions. For example, lithium hydride (LiH) is a common ionic hydride used in various applications, from synthetic chemistry to hydrogen storage.

When analyzing problems related to ionic hydrides, it's important to remember that they are commonly formed with metals located in groups 1 and 2 of the periodic table. An incorrect match, such as a transition metal forming an ionic hydride, may indicate a misunderstanding of the fundamental properties and formation of ionic hydrides.

Molecular Hydrides

Molecular, or covalent, hydrides consist of hydrogen atoms covalently bonded to non-metal atoms. These compounds, such as water (H₂O) and methane (CH₄), are formed with elements from group 14 and beyond on the periodic table, including carbon, nitrogen, and oxygen.

The formation of molecular hydrides involves sharing of electrons between the hydrogen and the non-metal atoms, resulting in discrete molecules. These substances can be gases, liquids, or low-melting solids and have a wide range of chemical and physical properties, depending on the non-metal they are bonded to.

During exercises, recognizing that elements such as phosphorus form molecular hydrides is essential, as they are typically found in a gaseous or volatile state under standard conditions and exhibit properties vastly different from their ionic or interstitial counterparts.

Interstitial Hydrides

Interstitial hydrides are formed when hydrogen atoms occupy the interstices (gaps) in a metal lattice, typically metals from the d-block or f-block of the periodic table. Transition metals like vanadium, niobium, and palladium are known to form such hydrides.

These substances do not change the primary metal structure but rather fill the spaces within it, leading to a variety of properties that differ based on the host metal. Interstitial hydrides can exhibit metallic properties such as electrical conductivity and are often found to be non-stoichiometric, meaning the ratio of metal to hydrogen atoms can vary.

Keep in mind that interstitial hydrides are not commonly associated with s-block elements, as their larger metallic frameworks are not suitable for the relatively small hydrogen atoms to fit within. When examining the formation of interstitial hydrides, it’s necessary to focus on those metals that can create the appropriate crystal lattice to accommodate hydrogen atoms.