Hydride, in simple terms, is said to be the anion of hydrogen. It is a chemical compound where the hydrogen atoms exhibit nucleophilic, basic or reducing properties. Usually, in a hydride, the hydrogen has an oxidation number equal to −1. Some popular examples include water (H2O), methane (CH4) and ammonia (NH3).
What Are Hydrides?
Compounds of hydrogen with less electronegative elements are known as hydrides. So, when hydrogen reacts with any other element, the product formed is considered to be a hydride. If we closely observe the periodic table, hydride formation is not seen from VA group elements, and this condition is known as the hydride gap. Hydrogen molecule usually reacts with many elements except noble gases to form hydrides. However, the properties may vary depending on the type of intermolecular force that exists between the elements, their molecular masses, temperature, and other factors.
Types of Hydrides
Hydrides are mainly divided into three major types or groups. The categories are decided based on what elements the hydrogen forms bonds with or simply on the basis of chemical bonding. The three types of hydrides are ionic, covalent, and metallic hydrides. We will learn about them in detail below.
Ionic or Saline Hydrides
They are formed when hydrogen molecule reacts with highly electropositive s-block elements (Alkali metals and alkaline earth metals). In solid-state, the ionic hydrides are crystalline, non-conducting and non-volatile. However, in a liquid state, they conduct electricity. Ionic hydrides on electrolysis liberate hydrogen gas at the anode. Saline or ionic hydrides do not dissolve in conventional solvents, and they are mostly used as bases or reducing reagents in organic synthesis.
Example of Ionic Hydrides: Nah, KH, CaH2, etc. They contain hydrogen as the negatively charged (H–) ion.
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Covalent hydrides are formed when hydrogen reacts with other similar electronegative elements like Si, C, etc. The most common examples are CH4 and NH3. In general, compounds that are formed when hydrogen is reacted with non-metals are called covalent hydrides. The compounds share a covalent bond and are either volatile or non-volatile compounds. Covalent hydrides are also either liquids or gases.
Example of Covalent Hydrides: SiH4 (silane).
A hydrogen compound that forms a bond with another metal element is classified as a metal hydride. The bond is mostly covalent type, but sometimes the hydrides are formed with ionic bonds. These are usually formed by transition metals and are mostly non-stoichiometric, hard, high melting and boiling points.
Examples of Metallic Hydrides: TiH aluminium, cadmium, magnesium, etc.
Metal hydrides are also known as interstitial hydrides. They are formed when hydrogen molecule reacts with the d- and f-block elements. Metals of Groups 7, 8, and 9 do not form hydrides. They do conduct heat and electricity but not to the extent of their parent metals.
Uses of Hydride
- They are used as reducing agents in many chemical industries.
- Hydrides are highly significant in battery storage technologies such as nickel hydride batteries.
- They are used as drying agents.
- They are used as strong bases in organic synthesis.
- Metal hydrides are also used for their heat storage, hydrogen storage and compressors capabilities.