Which alkali metals form ionic hydrides?

All alkali metals form ionic (or saline) hydrides. These compounds are characterized by the presence of the negatively charged hydride ion ($H^{-}$) and are typically produced through the direct reaction of the metal with hydrogen at elevated temperatures (300–700 °C).1

While all alkali metals form these hydrides, their reactivity varies. For instance, lithium forms a relatively stable hydride, whereas the hydrides formed by the other alkali metals are notably more reactive. These saline hydrides are generally white crystalline solids that react vigorously with water to produce hydrogen gas and hydroxide ions. Common examples of these binary compounds include sodium hydride (NaH).21