Question

Out of \(\mathrm{LiH}, \mathrm{CaH}_{2}\) and \(\mathrm{CuH}\) (a) All are covalent hydrides (b) \(\mathrm{LiH}\) is ionic, \(\mathrm{CaH}_{2}\) and \(\mathrm{CuH}\) are intermediate hydrides (c) All are ionic hydrides (d) \(\mathrm{LiH}, \mathrm{CaH}_{2}\) are ionic and \(\mathrm{CuH}\) is covalent hydride

Short answer

Option (d): LiH and CaH2 are ionic; CuH is a covalent hydride.

Step-by-step solution

Understanding Hydride Types

Hydrides can be categorized as ionic, covalent, or metallic (intermediate). Ionic hydrides generally form when hydrogen reacts with alkali or alkaline earth metals, covalent hydrides involve s and p-block nonmetals, and metallic hydrides involve transition metals.

Analyzing LiH

LiH, or lithium hydride, is composed of lithium, an alkali metal, which typically forms ionic bonds. Hence, LiH is classified as an ionic hydride.

Analyzing CaH2

CaH2, or calcium hydride, consists of calcium, an alkaline earth metal, which often participates in ionic bonding. Therefore, CaH2 is an ionic hydride.

Analyzing CuH

CuH, or copper(I) hydride, involves copper, a transition metal. Such elements can form metallic or covalent bonds. However, copper hydride is known to exhibit covalent characteristics due to the low oxidation state 'Cu+' and hydrogen's electronegativity.

Combining Insights

From the analysis, we see that LiH and CaH2 are ionic hydrides whereas CuH is a covalent hydride. This means option (d) correctly describes the nature of these hydrides.

Key concepts

covalent hydrides

Covalent hydrides arise when hydrogen forms bonds with nonmetals, specifically elements that are in the s and p blocks of the periodic table. These hydrides are characterized by the sharing of electrons between hydrogen and another atom, creating a covalent bond. Due to the nature of these elements, covalent hydrides have diverse properties and can be gases like methane or liquids like water.
Here are some examples and their features:

• Properties vary widely: from water's ability to dissolve many substances to methane's inability to do so.
• Most covalent hydrides are non-conductive because they do not have free electrons.
• Often serve as functional groups or linkages in molecules used in organic chemistry.

Understanding covalent hydrides involves recognizing how electronic configurations affect the characteristics and reactivity of different compounds.

metallic hydrides

Metallic hydrides, sometimes referred to as interstitial or intermediate hydrides, occur when hydrogen atoms occupy spaces within a metallic lattice. Common with transition metals, these hydrides are notable for their complex relationship between metal and hydrogen.
Key points include:

• The metal framework often maintains its structure, allowing hydrogen to move freely within it.
• These compounds exhibit metallic properties such as electrical conductivity and malleability.
• In many cases, the hydrogen atoms can easily be removed, resulting in reversible hydrogen storage making these hydrides vital for hydrogen fuel applications.

Due to these unique characteristics, metallic hydrides play a significant role in advanced materials and energy storage technologies.

transition metals

Transition metals are a large class of elements characterized by their ability to form various oxidation states, typically found in the d-block of the periodic table. These metals are unique because they can form different types of bonds, including both metallic and covalent.
Highlights of transition metals include:

• They frequently form complexes with a wide range of ligands.
• They have high melting and boiling points due to strong metallic bonding.
• The d orbitals allow them to form colored compounds, which are used in various industries such as dyes and pigments.
• They are often catalyst materials due to their ability to lend electrons to reactants.

Understanding transition metals is crucial for explaining their role in creating unique compounds like covalent and metallic hydrides.