Oxides, Hydroxides, Hydrides,
and the
Strength of Acids and Bases


Consider Metal Hydroxides (soluble)

Clearly, these are electrolytes that produce stoichiometric quantities of OH- so they are all strong bases

Danger!! Sometimes metal ions form covalent 'coordination' complexes with OH- or H2O, making their solubility/acidity highly 'irregular' Such Coordination Complexes will be studied in later courses, NOT here.

Consider Non-Metal Hydroxides

These species are Acids because the weak bond is the O--H+ bond releasing H+ upon dissolution

Consider "organic" hydroxides
Don't forget 'Resonance' and the Carboxylic Acid ....

Metal Oxides are STRONG Bases because they hydrate to form metal hydroxides

Non-metal Oxides may hydrate to form acids

Organic Oxides are not good acids or bases

Examples:

Ketones

Ethers

Epoxides

The Periodic Properties of the Elements, , in Acid / Base terms, are not as powerful as one might think. This is because the origin of the acidity (or basicity) of a molecules is more related to the overall structure of the molecule than any single bond or atom, as we discussed above. However, some features may be commented on.

Across a row (period) of the periodic table, increasing electronegativity make the H-X bond more polar, or ionic, and thus more like H+ - X-. Therefore acidity should increase.

Ka:       NH3 < H2O < HF



Down a column (group) of the Periodic Table, the size increase of the element makes the H-X bond strength decreases. Thus the acidity will increase down the group:



Ka:       HF < HCl < HBr < HI

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