Metals are electropositive in nature. They generally have 1, 2 or 3 electrons in their valence shells and readily lose these electrons to form positively charged ions (cations).
These cations are stable as they acquire noble gas configuration after losing the valence shell electrons.
Na (g) → Na+ (gas) + e–
During electrolysis of their aqueous solutions they are discharged at the cathode. On the other hand non-metals are electronegative in nature. They generally have 5, 6 or 7 electrons in their valence shells. They have tendency to form anion by gaining electrons.
Cl (g) + e– → Cl– (g)
Most metals react with oxygen to produce metal oxides which are basic in nature. The reaction may take place without heating as in sodium, calcium or potassium, while some metals react with oxygen on heating to form oxides.
4Na (s) + O2 (g) → 2Na2O (s)
Mg (s) + O2 (g) → 2MgO (s)
4Al (s) + 3O2 (g) → 2Al2O3 (s)
Oxides of metals are basic in nature as they react with water and form bases.
Na2O (s) + H2O (l) → 2NaOH (aq)
CaO (s) + H2O (l) → Ca(OH)2 (aq)
Oxides of aluminium (Al2O3), zinc (ZnO), tin (SnO) and iron (Fe2O3) are amphoteric in nature as they react with acids as well as with bases.
Al2O3 (s) + 6HCl (aq) → 2AlCl3 (aq) + 3H2O (l)
Al2O3 (s) + 2NaOH (aq) → 2NaAlO2 (aq) + H2O (l)
Some metals react with water to produce metal hydroxides and hydrogen gas. Hydroxides are basic in nature.
Sodium and potassium react with cold water.
2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g)
2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g)
Magnesium reacts with hot water.
Mg (s) + H2O (l) → Mg(OH)2 (aq) + H2 (g)
Metals like Al or Fe react on heating with water or with steam. In these conditions metals form metal oxides.
2Al (s) + 3H2O (g) → Al2O3 (s) + 3H2 (g)
Fe (s) + 4H2O (g) → Fe3O4 (s) + 4H2 (g)
Metals react with acids like dilute HCl and dilute H2SO4 and produce metal salts and hydrogen gas (H2).
Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g)
Zn (s) + H2SO4 (aq) → ZnSO4 (aq) + H2 (g)
Some metals like aluminum and zinc react with common bases.
Sn (s) + 2NaOH (aq) + H2O (l) → Na2SnO3 (sodium stannate)
Zn (s) + 2NaOH (aq) → Na2ZnO2 (Sodium zincate)