explain why metal oxides tend to be basic if the oxidation number of the metal is low and acidic if the oxidation number of the metal is high
Group I, II oxides tend to form hydroxides, which in water are basic. Higher groups oxides form weak acids in water. See http://www.britannica.com/science/oxide
Metal oxides tend to be basic when the oxidation number of the metal is low because they tend to donate electrons to other compounds or species. On the other hand, metal oxides tend to be acidic when the oxidation number of the metal is high because they have a greater tendency to accept electrons from other compounds or species. Let's break down the explanation further.
The acidity or basicity of a metal oxide is related to the behavior of the metal atom in the oxide and its ability to donate or accept electrons. The oxidation number of the metal in the metal oxide plays a crucial role in determining its behavior.
When the oxidation number of the metal is low, it means that the metal has fewer electrons in its outermost shell. This indicates that the metal atom has a high tendency to lose electrons and form positive ions. In the metal oxide, the metal atom easily donates its electrons to other compounds or species, resulting in the formation of hydroxide ions (OH-) when the metal oxide reacts with water. These hydroxide ions confer basic properties to the metal oxide. Examples of metal oxides that exhibit basic properties include sodium oxide (Na2O) and magnesium oxide (MgO).
Conversely, when the oxidation number of the metal is high, it means that the metal has more electrons in its outermost shell. This indicates that the metal atom has a higher tendency to accept electrons and form negative ions. In the metal oxide, the metal atom readily accepts electrons from other compounds or species, leading to the formation of oxide ions (O2-) when the metal oxide reacts with water. These oxide ions impart acidic properties to the metal oxide. Examples of metal oxides that exhibit acidic properties include chromium trioxide (CrO3) and manganese dioxide (MnO2).
In summary, the behavior of metal oxides as either basic or acidic depends on the oxidation number of the metal in the metal oxide. A lower oxidation number indicates a tendency to donate electrons, resulting in basic properties, while a higher oxidation number suggests a tendency to accept electrons, leading to acidic properties.