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Hydrogen forms hydrides when it reacts with any element in the periodic table except noble gases. Hydrides have a general formula H^- through which they can be classified. It can also be defined as the compound of hydrogen with a less electronegative element. Many factors affect the formation of hydrides, such as molecular masses, temperature, and intermolecular forces between the elements.

Ionic hydrides: When a hydrogen molecule reacts with any of the alkali and alkaline earth metals of Group 1 and 2, respectively, also known as electropositive s-block elements, it results in the formation of an ionic hydride, for example, LiH, NaH and KH.

Covalent hydrides: When hydrogen is reacted with non-metals or electronegative elements such as silicon in the periodic table, it results in the formation of covalent hydrides. These hydrides are present in liquid or gaseous forms, for example, silane.

Metallic hydrides: These are generally formed by the reaction between hydrogen atoms and metals such as Group D and F-block elements. These are also known as transition hydrides due to their forming a covalent bond between a transition metal and a hydrogen molecule—for example, TiH (titanium hydride).

The areas containing elements that give rise to the three types of hydrides are labelled below in the diagram of the periodic table: