PROPERTIES OF THE PERIOD 3 "HYDROXIDES"

PROPERTIES OF THE PERIOD 3 "HYDROXIDES"

This page looks briefly at how the chemistry of the "hydroxides" of the Period 3 elements from sodium to chlorine varies as you cross the period.

I am taking the word "hydroxide" to include anything which contains either a hydroxide ion or an -OH group covalently bound to the element in question. You wouldn't usually think of some of the compounds on this page as hydroxides at all.

A quick summary of the trends

Sodium and magnesium hydroxides

These contain hydroxide ions, and are simple basic hydroxides.

Aluminium hydroxide

Aluminium hydroxide, like aluminium oxide, is amphoteric - it has both basic and acidic properties.

The other "hydroxides"

All of these have -OH groups covalently bound to the atom from period 3. These compounds are all acidic - ranging from the very weakly acidic silicic acids (one of which is shown below) to the very strong sulphuric or chloric(VII) acids.

There are other acids (also containing -OH groups) formed by these elements, but these are the ones where the Period 3 element is in its highest oxidation state.

Adding some detail

Sodium and magnesium hydroxides

These are both basic because they contain hydroxide ions - a strong base.

Both react with acids to form salts. For example, with dilute hydrochloric acid, you get colourless solutions of sodium chloride or magnesium chloride.

Aluminium hydroxide

Aluminium hydroxide is amphoteric.

Like sodium or magnesium hydroxides, it will react with acids. This is showing the basic side of its nature.

With dilute hydrochloric acid, a colourless solution of aluminium chloride is formed.

But aluminium hydroxide also has an acidic side to its nature. It will react with sodium hydroxide solution to give a colourless solution of sodium tetrahydroxoaluminate.