periodicity refers to trends or recurring variations in element properties with increasing atomic number

P,S,CL is like that because P will form P4, S will form S8 and Cl will form Cl2

• The electrical conductivity increases from Na to Al because the number of electrons contributed by per atom to the sea of delocalized electrons increases from one in Na to three in Al. Thus there are more electrons to conduct electricity

• The electrical conductivity decreases from Al onwards because Si is a semi-metal therefore it is semi-conductor. The remaining elements do not conduct electricity because they have no mobile electrons

• Sodium burns on heating oxygen vigorously with an orange-yellow flame to form white sodium oxide

4Na(s) + O2(g) = 2Na2O(s)

• Magnesium burns on heating oxygen vigorously with a brilliant white flame to form white magnesium oxide

2Mg(s) + O2(g) = 2MgO2(s)

• An oxide layer will form on the aluminium when it is exposed to air, this oxide layer prevents aluminium from reacting. However, if powdered aluminium is used, it burns on heating with white flames to form white aluminium oxide

4Al(s) + 3O2(g) = 2Al2O3(s)

• Silicon burns slowly at red heat to form silicon(IV) oxide or silicon dioxide

Si(s) + O2(g) = SiO2(s)

• Phosphorus burns on heating vigorously with a white flame to form clouds of white covalent oxides

P4(s) + 3O2(g) = P406(s), if oxygen gas is limited

P4(s) + 5O2(g) = P4010(s), if oxygen gas is in excess

• Sulfur burns gently on hitting with a blue flame to form sulfur dioxide gas

S(s) + O2(g) = SO2(g)

• Chlorine forms several oxides but it will not directly react with oxygen

• Argon does not react with oxygen for it is a noble gas

• Going across period 3, the reactivity towards oxygen decreases because the reducing power(tendency to be oxidized) of the elements decreases

• Sodium burns on heating vigorously in chlorine gas with an orange-yellow flame to form white sodium chloride or with cold and dilute alkali

2Na(s) + Cl2(g) = 2NaCl(s)

• Magnesium burns on heating in chlorine gas vigorously with a brilliant white flame to form white magnesium chloride

Mg(s) + Cl2(g) = MgCl2(s)

• Aluminium burns on heating vigorously to form ionic aluminium chloride, at temperature about 180*C aluminium chloride converts to a molecular form, AlCl3, a dimer of covalent Al2Cl6. At higher temperature, Al2Cl6 breaks into simple AlCl3 molecules

2Al(s) + 3Cl2(g) = 2AlCl3(s)

2Al(s) + 3Cl2(g) = 2AlCl6(s), dimer

• Silicon burns slowly in chlorine gas at red heat to form covalent silicon(IV) chloride or silicon tetrachloride

Si(s) + Cl2(g) = SiCl4(I)

• Phosphorus burns in chlorine gas slowly to produce a mixture of two chlorides, PCl3 if chlorine gas is limited and PCl5 if chlorine gas is in excess

P4(S) + 6Cl2(g) = 4PCl3(I), if chlorine gas is limited

P4(s) + 10Cl2(g) = 4PCl5(I), if chlorine gas is excess

• Sulfur burns in chlorine gas to produce disulfur dichloride, an orange, stinky liquid (not in syllabus)

• Argon does not react with chlorine gas

• Sodium catches fire in cold water and a violently exothermic reactions occurs to form sodium hydroxide and hydrogen gas

2Na(s) + 2H20(I) = 2NaOH(aq) + H2(g)

• Magnesium reacts very slowly with cold water, taking several days to collect a test tube of hydrogen gas and a wealthy alkaline magnesium hydroxide and hydrogen gas

Mg(s) + 2H20(I) = Mg(OH)2(aq) + H2(g), very slow

However, it reacts rapidly with steam to produce magnesium hydroxide and hydrogen gas

Mg(s) + 2H20(g) = MgO(s) + H2(g), very fast

• Sodium oxide reacts exothermically with cold water to form sodium hydroxide. A strongly alkaline solution of sodium hydroxide is produced

Na2O(s) + H20(I) = 2NaOH(aq), pH=13

• Magnesium oxides reacts slightly with water to the extent that it is almost insoluble. A weakly alkaline solution of magnesium hydroxide is produced. Magnesium oxides and hydroxides settle indigestion problems

MgO(s) + H20(I) = Mg(OH)2(aq), pH=9

• Aluminium oxides does not react or dissolve in water due to its high lattice energy

• Silicon (SI) dioxide does not react with or dissolve in water due to the strong covalent bonds

• Phosphorus oxides react with water to form acidic solutions(PH=2)

P4O10(s) + 6H20(I) = 4H3PO4(aq)

• Sulfur oxides react with water to form acidic solutions

SO3(g) + H20(I) = H2SO4(aq)

• Sodium chloride dissolves in water to form a neutral solution of sodium chloride

NaCl(s) + aq = Na+(aq) + Cl-(aq), pH=7

• Magnesium chloride dissolves in water with slight hydrolysis to form a solution of magnesium chloride

MgCl2(s) + 6H20( = Mg2+ + 2Cl-, pH=6.5

• Aluminium chloride hydrolyses in water to give an acidic solution, white fumes of hydrogen chloride gas are formed

AlCl3(s) + 6H20(I) = [Al(H20)6]3+(aq) + 3Cl-(aq)

[Al(H20)6]3+(aq) + H20(I) ⇌ [Al(H20)5(OH)]2+(aq) + H30(aq), pH=3

• Silicon tetrachloride undergoes complete hydrolysis in water to form a strongly acidic solution, white fumes of hydrogen chloride gas are formed

SiCl4(I) + 2H20(I) = SiO2(s) + 4HCl(g), pH=2

• Phosphorus(III) chloride reacts violently with water in a hydrolysis reaction to give a strongly acidic solution with fumes of hydrogen chloride gas

PCl5(I) + 4H20(I) = H3PO4(aq) + 5HCl(g), pH=2

• Both chlorine and argon chlorides does not react with water

• The acidity of the chlorides increase across the period as the nature of the chlorides changes form ionic to covalent