| Group 1 | Group 2 | Group 13 |
Li+ at all pH
basic oxide (Li2O) | low pH high pH
Be2+,Be(OH)42–
amphoteric oxide (BeO) | low pH high pH
B(OH)3, B(OH)4–
acidic oxide (B2O3) |
Na+ at all pH
basic oxide (Na2O) | low pH high pH
Mg2+ Mg(OH)2
basic oxide (MgO) | low pH high pH
Al3+, Al(OH)4–
amphoteric oxide (Al2O3) |
K+ at all pH
basic oxide (K2O) | low pH, high pH
Ca2+ Ca(OH)2
basic oxide (CaO) | low pH high pH
Ga3+, Ga(OH)4–
amphoteric oxide (Ga2O3) |
Rb+ at all pH
basic oxide (Rb2O) | Sr2+ at all pH
basic oxide (SrO) | low pH high pH
In3+ In(OH)4–
amphoteric oxide (In2O3)
(more basic than acidic) |
Cs+ at all pH
basic oxide (Cs2O) | Ba2+ at all pH
basic oxide (BaO) | Tl+ at all pH
basic oxides (Tl2O and Tl2O3) |
Group 1, 2 and 13 elements exist in their compounds in their maximum oxidation state which is the last digit of the Group Number. As shown in the table at the right, the bottom elements in Group 13 also have a +1 oxidation state.
The table shows the diagonal trend in the acid-base properties of oxide/hydroxide and the nature of the species in aqueous solution.
Electropositive metals (white)
- have ions that exist as cation hydrates at all pH
- have basic oxides (dissolve in water to give OH– or, if insoluble, dissolve in aqueous acid)
Less electropositive metals (yellow)
- exist as insoluble oxides/hydroxides around pH 7
- exist in their positive oxidation states as cation hydrates in aqueous solutions of low pH and as hydroxoanions at high pH. The hydrated cations are weak acids.
- have amphoteric oxides that dissolve in both aqueous acid and base
Boron is a non-metallic element (green)
- which does not form a discrete cation but exists as a hydroxide at low pH and as a hydroxoanion at high pH.
- has an acidic oxide that reacts with hydroxide ion