(a) Na Mg Al Si P S Cl Ar

(b) 11 12 13 14 15 16 17 18

(c) 2.8.1 2.8.2 2.8.3 2.8.4 2.8.5 2.8.6 2.8.7 2.8.8

(d) 186 160 143 118 110 104 100 94

(e) s s s s s s g g

(f) 0.9 1.2 1.5 1.8 2.1 2.5 3.0 -

(a)Element of period 3(b) Proton number(c) Electron arrangement(d) Atomic radius (pm)(e) Physical state at room temperature(f) Electronegativity

Across period 3 - the proton number increases by one unit from one element to the next element - all the atoms of the elements have three shells occupied with electrons - the number of valence electrons in each atom increases from 1 to 8 - all the elements exist as solid except chlorine and argon which are gases - the atomic radius of elements decreases. This is due to the increasing nuclei attraction on the valence electrons - the electronegativity of elements increases. This is due to the increasing nuclei attraction on the valence electrons and the decrease in atomic size

Na Mg Al Si P S Cl

metal Semi metal

Non metal

Na2O MgO Al2O3 SiO2 P4O10 SO2 Cl2O7

Basic oxide Amphoteric oxide

Acidic oxide

Properties of oxides of element in Period 3

The oxides of the elements change from basic to amphoteric and then acidic across the period.

Metals form oxides with basic properties.

Eg: sodium oxide, magnesium oxide

Basic oxides react with acid to form a salt and water.

Eg : magnesium oxide react with hydrochloric acid to form magnesium chloride salt and water

MgO + 2HCl MgCl2 + H2O

An amphoteric oxide can react with both acids and bases to form salts and water.

In Period 3, aluminium oxide has amphoteric properties.

Al2O3 + 6HNO3 2Al(NO3)3 + 3H2O

Al2O3 + 2NaOH 2NaAlO2 + H2O

Non-metals form oxide with acidic properties.

Eg: sulphur dioxide, sulphur trioxide

Acidic oxides react with alkali to form a salt and water.

SO3 + H2O H2SO4

Argon as a noble gas does not forms any oxide.