Acidity/Basicity of Oxides (1 Viewer)

[Constip8edSkunk]

Can someone explain why there is this trend relating an element's position in the periodic table and the acidty of its oxides?

Across a period(left to right), the oxides first decrease in basicity until the element can form possible amphoteric oxides, and then increases in acidity.
Down a group, the oxides increases in basicity.

I heard it can be related to electronegativity in some ways which i didnt really understand.

Thanks in advance.

 

[spice girl]

The long explanation:

1. Low electronegativity: the metal-oxygen bond is ionic. The oxide acts as a O^2- ion. This reacts with water (hydrates) to form hydroxide, which then dissociates:

e.g. Na2O(s) + H2O(l) -> 2Na+ + 2OH-

2. High electronegativity: the non-metal-oxygen bond is covalent. This means under hydration it doesn't come off, unlike the example above. But because the oxygen is still more electronegative than the central atom (e.g. carbon in carbon dioxide) the carbon is delta-positive and wants electrons (electrophilic). It acts as a lewis base, accepting the electron pair from the oxygen from H2O. In hydration, the H2O becomes the base, which means the oxide becomes the acid:

CO2 + H2O -> H2CO3 (carbonic acid)

3. Amphoteric: This is basically when the metal-oxygen bond is ionic (as in case 1), so reacts as a base. As well, the metal atom is acidic (for some odd reason), and if it is allowed to react with base , the hydroxide hangs on (complexes) with the metal.

e.g. ZnO + H2O -> Zn(OH)2
Zn(OH)2 + 2OH- -> Zn(OH)4 2-

Short explanation: metal oxides are basic, non-metal oxides are acidic, because IT IS...

 

[Constip8edSkunk]

ok i got it thanx.