22.1 Reactions of period 3 elements

They are metallic So are shiny when first exposed to air, conduct electricity, and react with dilute acids to give hydrogen and salts

. Metalloid so conducts electricity to some extent which is useful

. Non-metals They don’t conduct electricity and have low melting and boiling points

It’s a noble gas, chemically unreactive

Sodium and magnesium

. Vigorous reaction . Sodium floats on top of the water and fizzes rapidly . It melts because of the heat energy released by the reaction . A strongly alkaline solution of sodium hydroxide is formed

2Na(s) +2H20(l) –> 2NaOH(aq) + H2(g)

. It is a very slow reaction at room temperature . Only a few bubbles of hydrogen are formed after days The resulting solution is less alkaline than with sodium because magnesium hydroxide is only sparingly soluble (PH 10)

. React magnesium with steam Mg(s) + H20(g) –> MgO + H2(g) Its a redox reaction as the oxidation state of the metal increases from 0 to 2+ and that of the hydrogen decreases from 1+ to 0

Mg(s) + 2H20(l) —> Mg(OH)2(aq) + H2(g)

All elements in period 3 are relatively reactive so directly react with it. 2Na(s) +1/2O2(g) –> Na2O(s) Sodium burns brightly in air with a yellow flame to form white sodium oxide

2Mg(s) + O2(g) —> 2MgO(s) It makes magnesium oxide

A strip of magnesium ribbon burns in air with a bright white flame. It produces a white powder called magnesium oxide

When aluminium powder is heated and then lowered into a gas jar of oxygen, it burns brightly to make aluminium oxide which is a white powder

4Al(s) + 3O2(g) —> 2Al2O3(s)

. Its oxide forms a strongly bonded protective layer over it which protects it from reacting even further That’s why aluminium is seen as an unreactive metal and has everyday uses eg saucepan or window frame

Silicon will also form an oxide if heated strongly in oxygen Si(s) + O2(g) –> SiO2(s)

. Red phosphorus must be heated before it will react with oxygen . White phosphorus spontaneously ignites in air and the white smoke of phosphorus pentoxide is given off Red and white are allotropes of phosphorus- the same element with the particles arranged differently

4P(s) + 5O2(g) –> P4O10(s) Makes phosphorus pentoxide P2O3 phosphorus trioxide is formed

.When sulfur powder is heated and lowered into a glass jar of oxygen . It burns with a blue flame to form colourless gas sulfur dioxide (and a little sulfur trioxide also forms)

S(s) + O2(g) —> SO2(g)

. The oxidation state of the period 3 element increases so that of oxygen decreases from O to -2 in each case The oxidation number of the period 3 element increases across the period