--- title: "Metal Hydrides | Intro to Chemistry" description: "Metal hydrides are compounds of hydrogen with a metal, ranging from ionic to interstitial forms, and they show up in hydrogen storage, reduction, and bonding." canonical: "https://fiveable.me/intro-chem/key-terms/metal-hydrides" type: "key-term" subject: "Intro to Chemistry" unit: "Unit 18" --- # Metal Hydrides | Intro to Chemistry ## Definition Metal hydrides are compounds made from hydrogen and a metal. In Intro to Chemistry, they show how hydrogen can act as a hydride, form different bond types, and store or release hydrogen gas. ## What It Is Metal hydrides are compounds that contain hydrogen bonded with a metal, and Intro to Chemistry usually treats them as a way to study how hydrogen behaves in different bonding situations. The big idea is that not all hydrides are the same. Depending on the metal and the structure, the hydrogen can behave like an ion, sit in the spaces between metal atoms, or form more covalent bonds in a molecular compound. The simplest version to remember is ionic hydrides, which form when very reactive metals, especially alkali and alkaline earth metals, combine with hydrogen. In these compounds, hydrogen acts like the hydride ion, H-. Lithium hydride, LiH, and sodium hydride, NaH, are classic examples. Because the hydrogen is electron-rich in this form, ionic hydrides are strongly basic and often used as reducing agents in chemical reactions. Another major category is interstitial hydrides. These form when small hydrogen atoms fit into the gaps inside a metal lattice, rather than making a simple electron-transfer compound. Palladium hydride is a common example often discussed in chemistry because palladium can absorb large amounts of hydrogen. When hydrogen slips into the metal structure, the metal can change in volume and electrical behavior, which is why these materials are useful in hydrogen storage and materials chemistry. Covalent hydrides are a little different because the bonding is more molecular than metallic or ionic. They are not always classified the same way in every intro course, but they matter because they show that hydrogen forms many kinds of compounds, not just simple salts. Diborane, B2H6, is a famous example because it has unusual bonding and is very reactive. A useful way to think about metal hydrides is to connect structure to behavior. If the metal is highly electropositive, the hydride is more likely to be ionic. If the metal has a crystal structure that can accommodate hydrogen atoms, you may get an interstitial hydride. The size of the metal, the electronegativity difference, and the arrangement of atoms all affect how stable the hydride is and what reactions it can do. ## Why It Matters Metal hydrides show up in Intro to Chemistry when you are connecting bonding theory to real chemical behavior. They give you a concrete example of how the same element, hydrogen, can act differently depending on the other element it bonds with and the structure it forms. This term also links several course topics together. In bonding units, hydrides help you compare ionic and covalent bonding. In reactions, they come up as reducing agents because hydride sources can donate electron density to other compounds. In materials chemistry, interstitial hydrides show how atoms can fit into a metal lattice and change physical properties like volume, resistance, and gas uptake. Metal hydrides are one of the clearest ways to see that chemical formulas do not tell the whole story by themselves. LiH and PdH2 both involve hydrogen and a metal, but they behave very differently because their structures are different. That makes hydrides useful for practice questions that ask you to classify compounds, predict reactivity, or explain why a substance stores hydrogen well. They also connect to hydrogen preparation and storage. Since hydrogen gas is hard to keep in a small, safe form, hydrides give chemists a way to absorb and release hydrogen under controlled conditions. That shows up in class when you compare industrial uses, lab handling, and how bonding affects a substance's properties. ## Connections ### [Hydride Ion](/intro-chem/key-terms/hydride-ion) Metal hydrides are often the place where you first see the hydride ion, H-. In ionic hydrides, hydrogen gains electron density and behaves like a negative ion rather than the usual proton-like hydrogen many students expect. That is why these compounds can act as strong bases and reducing agents. ### Ionic Hydrides Ionic hydrides are the most straightforward kind of metal hydride to classify. They usually form with very electropositive metals, and the hydrogen is present as H-. If you can identify an ionic hydride, you can often predict basicity, reactivity with water, and reducing behavior. ### Interstitial Hydrides Interstitial hydrides are the version of metal hydrides tied to metals with lattices that can absorb hydrogen atoms into their empty spaces. These compounds are less about simple ion formation and more about how the metal structure changes. That is why they are often discussed with hydrogen storage and materials properties. ### [Steam-Methane Reforming](/intro-chem/key-terms/steam-methane-reforming) Steam-Methane Reforming is a major hydrogen production method, and metal hydrides connect to it because the hydrogen produced has to be stored, transported, or used in later reactions. Knowing hydrides helps you follow what happens after hydrogen is made, especially when storage or reaction pathways are discussed. ## On the AP Exam A quiz question might give you a formula like LiH, NaH, or PdH2 and ask you to classify the compound or predict its behavior. Your job is to decide whether the hydride is ionic, covalent, or interstitial, then connect that choice to reactivity, bonding, or physical properties. You may also see hydrides in short answer questions about reducing agents, hydrogen storage, or why a metal changes volume after absorbing hydrogen. In a problem set, the move is usually to identify the kind of hydride first, then explain what that tells you about the electrons and the structure. If a lab or discussion asks why a compound releases hydrogen gas, metal hydride behavior is a strong clue that absorption and release are tied to the bond type and lattice arrangement. ## Metal Hydrides vs Hydride Ion A hydride ion is just the H- species, while a metal hydride is the whole compound that contains hydrogen bonded with a metal. The ion is the building block in some hydrides, but the terms are not interchangeable. If the question asks about the compound, answer with the hydride material, not just the ion. ## Key Takeaways - Metal hydrides are compounds of hydrogen and a metal, but they do not all bond the same way. - Ionic hydrides contain hydride ion character, so they are often strong bases and reducing agents. - Interstitial hydrides form when hydrogen fits into spaces in a metal lattice, which can change the metal's size and electrical properties. - The type of metal and the structure of the solid help decide whether a hydride is stable, reactive, or useful for hydrogen storage. - In Intro to Chemistry, hydrides are a good example of how bonding controls properties you can actually predict. ## FAQs ### What is metal hydrides in Intro to Chemistry? Metal hydrides are compounds made from hydrogen and a metal. In Intro to Chemistry, they are used to show how hydrogen can bond in different ways, from ionic hydrides like LiH to interstitial hydrides such as palladium hydride. The term covers both the structure and the behavior of these compounds. ### Are metal hydrides ionic or covalent? They can be ionic, covalent, or interstitial depending on the metal and the arrangement of atoms. If the metal is very electropositive, the hydride is often ionic and the hydrogen acts like H-. Other metal hydrides are better described by lattice absorption or more unusual covalent bonding. ### Why are metal hydrides used for hydrogen storage? Some metals can absorb hydrogen into their structure and later release it under the right conditions. That makes hydrides useful for storing hydrogen in a more compact or controlled form than free gas. Palladium hydride is a classic example of this behavior. ### What is the difference between a metal hydride and the hydride ion? The hydride ion is the H- particle or ion itself. A metal hydride is the compound that contains hydrogen bonded with a metal, and in some cases the bonding is more complex than a simple H- plus metal ion picture. That distinction matters when you classify the compound or predict its properties. ## Related Study Guides - [18.5 Occurrence, Preparation, and Compounds of Hydrogen](/intro-chem/unit-18/5-occurrence-preparation-compounds-hydrogen/study-guide/yarj3SIsl8lxw3LP) ## About This Document Canonical Fiveable pages are available as Markdown at the same path plus `.md`. - [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns - [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing - [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`) - [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`) ## Structured Data ```json {"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/intro-chem/key-terms/metal-hydrides#resource","name":"Metal Hydrides | Intro to Chemistry","url":"https://fiveable.me/intro-chem/key-terms/metal-hydrides","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/intro-chem/key-terms/metal-hydrides#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:22:18.202Z","isPartOf":{"@type":"Collection","name":"Intro to Chemistry Key Terms","url":"https://fiveable.me/intro-chem/key-terms"},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/intro-chem/key-terms/metal-hydrides#term","name":"Metal Hydrides","description":"Metal hydrides are compounds made from hydrogen and a metal. 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