# Hydrides Classification > Hydride classification for JEE Chemistry with saline, covalent electron-deficient to rich, metallic interstitial with the hydride gap, and complex hydrides. - Canonical URL: https://prepelephant.com/topics/jee/chemistry/hydrides-classification - Exam / course: JEE · Subject: Chemistry - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Hydrides Classification", PrepElephant, https://prepelephant.com/topics/jee/chemistry/hydrides-classification ## Direct answer Binary hydrides sort by bond type into three working families plus a reagent shelf. Saline (ionic) hydrides of groups 1 and 2 — NaH, CaH2 — hold the H− ion, melt high, conduct in the molten state and hydrolyse briskly to hydrogen. Covalent (molecular) hydrides of the p-block, from CH4 through NH3, H2O and HF, are volatile discrete molecules, subdivided by electron count into electron-deficient (diborane), electron-precise (group 14) and electron-rich (ammonia, water, hydrogen fluoride with lone pairs). Metallic (interstitial) hydrides absorb hydrogen into d-block lattices as non-stoichiometric phases such as TiH1.73, and complex hydrides LiAlH4 and NaBH4 serve as the organic chemist's reducing agents. ## What you must remember - **Saline hydrides:** NaH crystallises in the rock-salt arrangement; CaH2 + 2H2O → Ca(OH)2 + 2H2 makes calcium hydride a drying agent; thermal stability of group 1 hydrides falls down the group, LiH the most stable. - **Boundary cases:** BeH2 and MgH2 are polymeric and covalent, not ionic — small polarising cations pull the bonding towards covalency (Fajans logic). - **Electron-deficient hydrides:** diborane's bridges are three-centre-two-electron bonds, making B2H6 a Lewis acid; it hydrolyses as B2H6 + 6H2O → 2B(OH)3 + 6H2. - **Electron-precise and electron-rich:** group 14 hydrides use every electron in σ bonds; NH3, H2O and HF keep lone pairs — Lewis bases and hydrogen-bond donors, which is why ammonia boils far above phosphine. - **Metallic/interstitial:** non-stoichiometric conducting phases such as TiH1.73, VH0.56 and LaH2.87; the hydride gap — metals of groups 7-9 around Mn, Fe, Co and Ni form few or no hydrides. - **Applications:** LaNi5 absorbs about six hydrogens per formula unit — the nickel-metal-hydride battery and hydrogen-storage logic. - **Complex hydrides:** LiAlH4 reduces most carbonyl compounds; NaBH4 is its mild, alcohol-solvent counterpart. - **Water-reactivity ladder:** saline hydrides react violently; silane and diborane hydrolyse; ammonia dissolves basic; methane stays inert — behaviour tracks bond polarity. ## Sorting an unknown hydride Classification questions hand you clues, and each clue votes. A crystalline solid with a high melting point that conducts when molten and releases flammable gas on water is saline — think CaH2 drying a solvent. A volatile liquid or gas of a p-block element is covalent; then count electrons: diborane cannot satisfy conventional two-centre bonds, so it bridges (electron-deficient), methane spends everything on σ bonds (precise), and ammonia banks a lone pair (rich, hence basic and hydrogen-bonded — the fact behind its anomalous boiling point). A metal powder that soaks up hydrogen reversibly at moderate pressure is an interstitial hydride; if the metal is iron or nickel, the expected answer is the hydride gap instead. A white crystalline solid used to reduce aldehydes in the laboratory is LiAlH4, a complex hydride that behaves ionic toward the counter-ion yet covalent through its bridging Al–H bonds. Sorting, in every case, is bond-type recognition wearing different clothes. ## The borderline cases examiners probe The hydrogen chapter left the JEE Main syllabus in the 2023-24 rationalisation, but hydride logic has not left the ecosystem: JEE Advanced retains hydrogen-family chemistry in its revised syllabus, LiAlH4 and NaBH4 appear every year inside organic reductions, and saline hydrides resurface in hydrogen-yield numericals (CaH2 with water is a classic). The examined edges are the boundaries. BeH2 and MgH2 wrongly filed as ionic by candidates who see a group 2 metal. Hydride-gap metals wrongly grouped with titanium and zirconium as absorbers. The electron-rich trio's boiling points — NH3 above PH3, H2O above H2S — presented as hydride facts that are really hydrogen-bond facts. And the double identity of H− as both strong base and strong reductant, which is why ionic hydrides both hydrolyse and reduce. Hold the boundary list and this page converts from memory work to reasoning. ## Frequently asked questions ### Name one hydride each of the saline, covalent and metallic types. NaH (ionic H− in a rock-salt lattice), CH4 or NH3 (discrete covalent molecules), and TiH1.73 (non-stoichiometric interstitial phase). ### Why are group 13 hydrides electron-deficient? Their valence electrons cannot fill conventional two-centre two-electron bonds, forcing bridged multi-centre bonding as in diborane's B–H–B links. ### Which metals resist hydride formation? The group 7-9 cluster around manganese, iron, cobalt and nickel — the hydride gap — absorbs little hydrogen, unlike early transition metals or palladium. ### Why does calcium hydride serve as a drying agent? It reacts stoichiometrically with traces of water, CaH2 + 2H2O → Ca(OH)2 + 2H2, stripping moisture from solvents and gases. ### What role do complex hydrides play in synthesis? LiAlH4 and NaBH4 deliver hydride to electrophilic carbon, reducing aldehydes, ketones, acids and esters to alcohols with different vigour and solvent tolerance.