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Introduction to Hydride

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Hydride is the anion of a hydrogen atom. Hydrogen can react with other elements of the periodic table. Nucleophilic, reducing, and basic properties can be found in the chemical compounds of hydrogen, and hydride. Hydride compounds are formed with all elements of the periodic table, except a few noble gases.

Depending on the element and the bond formed with hydride ions, the properties of that particular hydride compound can be described. Its molecular formula is H- and the molecular weight is 1.008 g/mol. Also, it is observed that the hydrogen atom doesn't react with the VA group elements in the periodic table. This is nothing but a hydride gap.

Types of Hydrides

Considering the chemical bonds and what type of elements can react with the hydrogen atom, these hydrides can be classified into three different types. They are - 

  • Ionic Hydrides

  • Covalent Hydrides

  • Metallic or interstitial hydrides

Each type of hydride is explained as follows.

Ionic Hydrides- The first type of classification is ionic hydrides. Saline hydrides, pseudohalides are the other names of ionic hydrides. These ionic hydrides are formed whenever the S block elements (which are known as alkaline fiesta metals) and other alkali metals react with hydrogen atoms forming electrovalent compounds. These are the most active elements in the periodic table. They behave differently in a solid-state and liquid state.

In solid-state, the ionic hydrides are non-volatile, non-conducting, and crystalline. Whereas in the liquid state, the ionic hydrides act as good conductors of electricity. Also in electrolysis, hydrogen gas is produced at the anode.

MH(s) + H2O(l) → MOH(aq) + H2(g)(3)

Examples of ionic hydrides are sodium hydride (NaH), potassium hydride (KH), calcium hydride (CaH2), etc. All alkali metal hydrides come under this category.

Covalent Hydrides- Another category of hydrides is covalent hydrides. These covalent hydrides are formed when one atom of hydrogen reacts with one or more nonmetal elements. Usually, the covalent bonds may be formed by elements in Groups 13 to 17. In contrast to the ionic hydrides, the covalent hydrides are formed with electronegative elements. The sharing of electron pairs can take place here. The covalent hydrides behave like both volatile and non-volatile compounds, based on the reaction.

Examples of covalent hydrides are boron hydrides, nitrogen hydrides, silicone hydride (which is saline), etc.

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Metallic or Interstitial Hydrides:- These are another category of hydrides. The interstitial hydrides are nonstoichiometric. It is their unique quality. Usually, these interstitial hydrides are formed by the bonding between a hydrogen atom and transition elements. Besides being nonstoichiometric, the interstitial or metallic hydrides are very hard in nature. They have high boiling points and high melting points. All the d block and the f block elements are transition elements. They can conduct electricity but are different when compared to the ionic hydrides. 

Magnesium hydride, aluminium hydride, cadmium hydride, etc. were considered as examples of these metallic hydrides.

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Binary Hydrides:- Besides all these types of hydrides, binary hydrides are another special category of hydrides. Barium hydride, aluminium hydride, cesium hydride, calcium hydride, lithium hydrides, etc are examples of binary hydrides. The binary hydrides contain an element that can bond with a hydrogen atom. After the chemical bonding, the hydrogen atom acts as electronegative species. In these binary hydrides, the existence of free hydride anions is very rare. 

Uses of Hydrides

Different types of hydrides have different applications in Chemistry. A few of those applications are listed below.

  • In organic chemistry, the lithium aluminium hydride acts as a powerful reducing agent for chemical reactions.

  • Ammonia is used in several industries.

  • Fumigation is a chemical process where phosphine is the key ingredient of the process.

  • Metal hydrides are used in multiple ways. This can be used to store heat, hydrogen and also used as compressors.

  • Hydrides are used as drying agents in the textile industry.

  • Nickel hydrides are well known for batteries and have a dominant role in battery technology industries.

  • Hydrides are widely used as reducing agents.

These are some applications of different hydrides. Along with these applications, many other uses of hydrides are there in various industries.

Thus, the hydrides are chemical compounds that are formed with the bonding of hydrogen atoms with other elements present in the periodic table. Based on the type of element and type of bond between them, these hydrides are classified into different types and each type is discussed above. Every hydride has its significance and altogether has several applications in Chemistry, industries, etc.

FAQ (Frequently Asked Questions)

1. What are the Properties of Ionic Hydrides?

Ans. The ionic hydrides are also known as saline hydrides. Some of the chemical properties of these ionic hydrides are as follows.

  • The ionic hydrides are solid crystalline in structure.

  • Usually, they appear whitish.

  • As ionic hydrides are stable, they have high density.

  • They have a high melting point and high boiling point when compared to the other hydrides.

  • Ionic hydrides also produce hydrogen gas and act as a good conductor of electricity. This reaction can be shown below.

CaH2 (melt) → Ca2+ + 2H-

At anode: 2H → H2 + 2e-

At cathode:   Ca2+ + 2e- → Ca

  • The ionic hydrides behave uniquely and vigorously with water, ammonia, and ethanol. However, they produce pure hydrogen gas and that's the reason they can be always kept in a moisture-free environment.

2. What are the Properties of Covalent Hydrides?

Ans. The properties of covalent hydrides are as follows. 

  • These hydrides have weak intermolecular forces and have individual covalent molecules.

  • Similar to the non-metallic compounds, covalent hydrides are also poor conductors of electricity.

  • The covalent hydrides have low melting points and low boiling points.

  • These can form the highest number of hydrides reacting with carbon.

  • They are more acidic in the periodic table.

  • They exhibit both volatile and non-volatile properties.

  • The sharing of electron pairs can be seen in the covalent hydrides.

These are the various characteristics of covalent hydrides which may differ from ionic hydrides and metallic hydrides.