Which of the group 1 metal hydrides is stable up to 900 °C? 

CONCEPT:

Group 1 Metal Hydrides Stability

• Metal hydrides are compounds formed between metals and hydrogen. The stability of these hydrides depends on the metal's position in the periodic table and the bond strength between the metal and hydrogen.
• Among Group 1 metals, lithium forms one of the most stable hydrides due to its small ionic size and strong electrostatic interactions with hydrogen.
• Stability at high temperatures is influenced by the strength of the metal-hydrogen bond and the lattice energy of the solid hydride.

EXPLANATION:

• In the given question, the hydrides of Group 1 metals are considered for their stability up to 900 °C.
• Potassium hydride (KH), Sodium hydride (NaH), Lithium hydride (LiH), and Caesium hydride (CsH) are hydrides of Group 1 metals.
• Lithium hydride (LiH) is the most stable hydride at high temperatures because:
  • Lithium is the smallest alkali metal, leading to a stronger metal-hydrogen bond compared to other Group 1 metals.
  • The high lattice energy of LiH contributes to its thermal stability.
• The hydrides of heavier alkali metals like potassium, sodium, and caesium are less stable at high temperatures due to weaker metal-hydrogen bonds and lower lattice energies.

Therefore, Lithium hydride (LiH) is the Group 1 metal hydride that is stable up to 900 °C.