Reactions of Alkali Metals

reactivity increases going down column !!!

1.  alkali metal + nonmetal à ionic compound

       special ex:

alkali metal + hydrogen  à  metal hydride  (H^-)

2.  alkali metal + water à H₂ gas and alkali metal hydroxide (exothermic, can ignite H₂ gas)

       K(s)  +  HOH (l) à

3.  alkali metal + oxygen 

       lithium:  forms lithium oxide (Li₂O)

       all other alkali metals: form peroxides  (O₂^2-)

2Na(s)   +  O₂(g)   --->  Na₂O₂(s)  sodium peroxide

K, Rb, and Cs can also form superoxides (O₂^-)

              K(s)   + O₂(g)   --->  KO₂(s)   potassium superoxide

peroxides and superoxides are unusual

most metals form metal oxides.

Group 2A      Alkaline Earth Metals

reactivity increases going down column !!!

       1.  alkaline earth metal + water

              beryllium: will not react, even when heated red hot 

              remaining:  form a metal hydroxide and hydrogen

       2.  alkaline earth metal + nonmetal à ionic compound

allotrope: different forms of the same element in the same state

       O₂ (g)    (dioxygen)           vs.         O₃ (g) Ozone