Alkalines

Alkalines

1. form 2+ ions

2. reactivity increases down group 2

3. when they react the are oxidised forming cations from 0 to +2

   • react with water to produce metal hydroxides & hydrogen
     • e.g.- 2Mg + 2H20 ---> 2MgOH +H2
   • burn in oxygen to produce white oxides
     • e.g.- 2Mg + O2 ---> 2MgO
   • the oxides react with water to produce metal oxides
     • MgO + H20 ---> Mg2+ + 2OH-
     • these dissolve to produce hydroxide ions which make solutions highly alkaline
       • MgO is the only exception reacting very slowly, and the hydroxide isn't very soluble

4. ionisation energies decrease as you got down the group

   • this is due to the increasing atomic radius and shielding effect

5. thermal decomposition

   • when a substance breaks down due to heat
   • group 2 carbonates decompose to produce the oxide and CO2
     • e.g.- MgCO3 ---> MgO + CO2
   • thermal stability increases down the group, e.g.- it takes more energy to decompose Ca than it does Mg

6. used to neutralise acidity

   • Ca(OH)2 used in agriculture to neutralise soils
   • Mg(OH)2 used in indigestion tablets as an antacid
   • OH- + H+ ---> H20