When alkali metals are heated with hydrogen they form what
hydrides. NaH, KH, LiH, etc.
When alkali metals, such as lithium, sodium, potassium, etc., are heated with hydrogen gas, they form a compound known as metal hydride. Metal hydrides are compounds that consist of alkali metal cations (positively charged ions) and hydride anions (negatively charged ions), which is H- in this case.
To determine the specific metal hydride formed when an alkali metal reacts with hydrogen, you can refer to the periodic table. The alkali metals are located in Group 1 (IA) of the periodic table, and they have a single valence electron. For example, let's consider sodium (Na) reacting with hydrogen (H2).
The reaction between sodium and hydrogen can be represented as follows:
2 Na + H2 → 2 NaH
This equation shows that when two atoms of sodium react with one molecule of hydrogen gas, they form two molecules of sodium hydride (NaH). This is a binary compound with sodium cations (Na+) and hydride anions (H-).
Similarly, other alkali metals will react with hydrogen to form their respective metal hydrides. For example, lithium reacts with hydrogen to form lithium hydride (LiH), while potassium reacts with hydrogen to form potassium hydride (KH).
Thus, when alkali metals are heated with hydrogen, they form metal hydrides such as NaH, LiH, KH, etc., depending on the specific alkali metal being used.