Oxides across a period

The compound an element forms by combining with oxygen is called the oxide of that element. Follow the oxides across a single period and a clear trend appears.

Element of period 3	Na	Mg	Al	Si	P	S	Cl
Oxide	Na₂O	MgO	Al₂O₃	SiO₂	P₂O₅	SO₃	Cl₂O₇
Acidic / basic nature	Strongly basic	Weakly basic	Amphoteric	Weakly acidic	Weakly acidic	Strongly acidic	Strongly acidic

Reading left to right: the acidic properties of the oxides increase and the basic properties decrease.

Reading the row

Sodium sits at the left of period 3 and its oxide is strongly basic. Magnesium oxide is weakly basic. From silicon through to chlorine the acidic character of the oxides increases.

Amphoteric oxides

Aluminium oxide shows both acidic and basic properties. Oxides like that are called amphoteric oxides — and notice where it falls: exactly at the turn between the basic side and the acidic side.

What this shows

So along a period, from left to right, the oxides formed become less basic and more acidic. Which is another way of saying what section 3.6 opened with: metals on the left, non-metals on the right.

Try this

Obtain a long-form periodic table and study it carefully. Report the information you can gather about the elements from it. Then choose one metal, non-metal or metalloid you have studied, collect information about it from your textbook, the internet and additional chemistry books, make a poster, and present it to the class.