L1 /   
9
CH1012
1A + O2
(b)    Reaction with oxygen
Group 1A + O2
Ø         lithium     ®   Li2O     (oxide; O2-)
Ø         sodium     ®  Na2O2  (peroxide; O22-)
Ø       K, Rb, Cs    ®  MO2  (superoxide; O2-)
• the differences are due to the different sizes of the anions and cations and the most stable ionic lattice that results.
eg. small cation + small anion ® stable solid
• Airpacks (firefighters) use O2 stored in KO2.