Before we proceed toward the complex terms related to hydrides, let us understand the basic meaning of hydrides. The term hydride is derived from the hydrogen atom. Likewise, any compound formed by the binding of the hydrogen atom is known as hydrides. Hydrides can react with mostly all metals and non-metals, except a few noble gases. Many types of hydrides are present in the world of inorganic chemistry.

These compounds’ physical and chemical properties depend on the type of bond shared between the elements. 

It is said that hydride is the negative part of the hydrogen atom. It has a negative charge. That is why there are so many variations when it forms a bond with the different elements. 

Definition of Hydride

Hydride is the negative counterpart of the hydrogen atom. Compounds that are called hydrides are always bonded to a more electropositive element. For instance, ammonia is a nitrogen hydride; even water is an oxygen hydride. Many such examples have hydrides in them.

Hydrogen bonds present with other elements are covalent. The density of a bond can be extreme or slight. However, there are some hydrides like boron hydride that form multi-centred bonds. On the other hand, interstitial hydrides have metallic bonding between them. There are many varieties of hydrides, such as polymers, oligomers, bulk metals, or ionic solids. Many act as reducing agents or strong bases, and many are hydrogen atom donors as well. 

Now that we have talked about hydrides’ definition, let us move on to the types of hydrides. The types of hydrides’ questions are important and should be studied thoroughly.

Types of hydrides

Hydrides are the extremely complex reason they are further divided into different types of hydrides. The differentiation of these hydrides is done based on the bond present between them. These bonds include covalent, ionic, and metallic bonds with different physical and chemical properties. That is why they react differently when they contact other elements.

The three types of hydrides are: 

• Ionic or Saline hydrides.
• Covalent hydrides.
• Metallic hydrides. 

Ionic or Saline hydrides

In this hydride type, hydrogen molecules bond with the s-block elements, which are highly electropositive. They are also known as alkali metals or alkaline earth metals. In this reaction, hydrogen reacts at a high temperature. Examples include NaH, CaH2, and KH. 

Properties of Ionic hydrides:

• They are mostly solids.
• Ionic hydrides are crystalline and do not conduct electricity because they cannot disperse ions easily.
• However, they conduct electricity when in liquid form.
• Ionic hydrides are not soluble in common solvents.
• These are often used as reducing agents.
• The compounds are white. They can become grey if metal impurities are present.
• Since Ionic hydrides are highly reactive with water, they also emit hydrogen gas. That is the reason they can be used as portable sources of hydrogen.
• Many ionic hydrides are also covalent. Examples include beryllium and magnesium hydrides. 
• Many commercial compounds and complex saline hydrides help reduce these elements.

Covalent hydrides

This hydride type is formed when covalency is present between the hydrogen and the non-metals. Generally, covalent hydrides are present in non-metals. Examples include H2O, HF, and NH3. 

Properties of covalent hydrides:

• They are both liquids and gases.
• They are non-volatile, with weak Van Der Waals intermolecular interactions between them.
• They have low melting and boiling points.
• They are formed by boron, aluminium, and gallium.
• As we move across the group, the compounds become more acidic. The only exception is hydrogen fluoride.
• Hydrogen fluorides have the highest boiling point.

Metallic hydrides

The metallic hydride is formed when a hydrogen molecule tends to react with metallic elements to form a covalent bond. However, they can have ionic bonds. Transition metals form these. Examples are MgH2 and NaAlH4. 

Properties of metallic hydrides:

• They have a high melting and boiling point.
• They are shiny.
• They conduct electricity properly.
• Some of them are brittle, while some are robust.
• They are the connecting link between salts and alloys.
• Metallic hydrides have positive hydrogen ions in them.
• Metallic hydrides are produced by combining hydrogen gas with metals or their alloys. 
• They are stable in air at a given temperature. However, they may react when heated in the air.
• They are greyish black solids.
• In metallurgy, they are used as reducing agents.

Conclusion 

In this module, we learned about the definition of hydrides and the types of hydrides. Various hydrides questions can be asked in examinations. This is why we explored the meaning of hydrides in our module. 

Hydrides refer to all compounds that have hydrogen atoms in them. There are many types of bonds that form with these compounds. They can be metallic, ionic, or even covalent bonds. The type of bonds present in the compounds determines the physical properties of these compounds. That is the reason we have also discussed the properties of hydrides. The three main hydrides are ionic, covalent, and metallic hydrides. Ionic hydrides have bonds of hydrogen with s-block elements. In covalent hydrides, the bond is formed between non-metals, and hydrogen and metallic hydrides form bonds with metals.