©MJC 2011 1

Meridian Junior College Summary of Periodic Table - Chemical Periodicity Physical Properties of Period 3 Element

Period 3 element Na Mg Al Si P S Cl Ar Atomic No. 11 12

13 14 15 16 17 18

Atomic Radius

Graph 1

Across the period, nuclear charge ↑ & negligible ↑ in shielding effect, effective nuclear charge ↑ atomic radius ↓

Ionic Radius

Graph 2

Formation of Cations Ionic Radius ↓ from Na+ to Si4+ as nuclear charge ↑ (each ion : Na+, Mg2+, Al3+, Si4+ have 10 e-)

Formation of Anions Ionic Radius ↓ from P3- to Cl- as nuclear charge ↑ (each ion : P3- , S2-, Cl- have 18 e-)

-

Melting pt

Graph 3

High m.p. due to giant metallic structure. There is strong metallic bonding. m.p. ↑ from Na to Al due to increasing metallic bond strength as no. of valence e- contributed per atom into sea of delocalised electrons ↑

Highest m.p. due to macromolecular structure. Numerous covalent bonds between Si atoms arranged tetrahedrally in a 3-Dimensional structure.

Low m.p. due to simple molecular structure. Weak van der waals forces between molecules. M.p of S8 > P4 > Cl2 > Ar due to decrease in size of electron cloud as no. of electrons decreases.

Electrical conductivity

Graph 4

High electricial conductivity, ↑ from Na to Al as no. of valence e- contributed per atom into sea of delocalised electrons ↑

Low electrical conductivity as Si is a metalloid

Non-conductor of electricity due to absence of delocalised electrons or mobile ions

First I.E

Graph 5

Generally 1st I.E. ↑ across period as nuclear chare g↑ and negligible increase in shielding effect, effective nuclear charge ↑ more energy required to remove the valence electron Lower 1st I.E of Al than Mg as the 3p e- in Al is at further away from the nucleus compared to 3s e- being removed in Mg; Lower 1st I.E of S than P as a paired 3p e- in S is removed which experiences inter-electron repulsion compared to an unpaired 3p e- in P.

Electronegativity

Graph 6

↑ across period as nuclear charge ↑ and negligible increase in shielding effect, Effective. nuclear charge ↑ across period.

©MJC 2011 2

Summary of Trends exhibited by Elements across Period 3

Atomic radius / nm

Na Mg Al Si P S Cl Ar

Ionic radius /nm

Proton numberNa Mg Al Si P S Cl

Si4+

Mg2+

Na+

P3- S2- Cl-

Al3+

Proton number

Graph 1 Graph 2

Electrical conductivity

Proton number Na Mg Al Si P S Cl Ar

Graph 3 Graph 4

first

Graph 5

Graph 6

©MJC 2011 3

Chemical Properties of Period 3 Element

Period 3 element Na Mg Al Si P S Cl Ar Reaction with

dry O2* Very vigorous Burns with yellow flame 2Na (s) + ½O2 (g) Na2O (s)

Very vigorous Burns with bright white flame Mg (s) + ½O2 (g) MgO (s)

Needs to be heated to 800 0C due to presence of the protective Al2O3 oxide layer 4Al (s) + 3O2 (g) 2Al2O3 (s)

Slow Needs to be strongly heated

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

Vigorous Forms a dense white smoke P4(s) + 3O2 (g) P4O6

(s) P4(s) + 5O2 (g) P4O10

(s)

Slow Burns with a blue flame With excess O2, SO2 is oxidised to SO3

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

--- ---

Reaction with dry Cl2*

Very vigorous Na (s) + Cl2 (g) 2NaCl (s)

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

Vigorous 2Al(s) + 3Cl2 (g) Al2Cl6 (s)

Slow Si (s) + 2Cl2 (g) SiCl4 (l)

Slow 2 chlorides (PCl3 & PCl5) formed PCl5 formed in excess Cl2 P4(s) + 6Cl2 (g) 4 PCl3 (s) P4(s) +10Cl2 (g) 4 PCl5 (s)

Slow

(Not required in syllabus)

--- ---

Reaction with cold water*

Reacts vigorously with water to form hydroxide & H2(g) 2 Na (s) + 2 H2O 2NaOH(aq) + H2 (g)

React very slightly with cold water but burns in steam. Mg (s) + H2O (g) MgO (s) + H2 (g)

Al reacts with steam. 2 Al(s) + 3 H2O (g) Al2O3 (s) + 3 H2

No reaction

©MJC 2011 4

Properties of Period 3 Oxides

Period 3 oxide

Na2O MgO Al2O3 SiO2 P4O6, P4O10 SO2, SO3

Oxidation No.

+1

+2 +3 +4 +3, +5 +4, +6

Oxidation no. of oxides ↑ across period as no. of valence e- available for bond formation ↑

Structure Giant Ionic Lattice Structure Giant molecular Structure

Simple molecular Structure

Nature of Oxide

Ionic & basic Ionic & amphoteric Covalent & acidic

Reaction with water*

Forms NaOH with water (pH ≈ 13) Na2O(s) + H2O(l) → 2NaOH(aq)

Forms Mg(OH)2 with boiling water (pH ≈ 9) MgO (s) + H2O(l)

Mg2+ (aq) + 2OH-(aq)

No reaction (pH = 7)

Al2O3 does not dissolve in water because of its extremely high lattice energy SiO2 - Large amounts of energy are required to break the numerous strong covalent bonds, solvation cannot occur.

Form H3PO3, H3PO4 with water (pH ≈ 2) P4O6(s) + 6H2O(l) 4H3PO3(aq) P4O10(s) + 6H2O(l) 4H3PO4(aq)

Form H2SO3, H2SO4 with water (pH ≈ 2) SO2(g) + H2O(l) H2SO3(aq) SO3(g) + H2O(l) H2SO4(aq)

Reaction with acid*

Form salt and water

Na2O(s) + 2HCl(aq) 2NaCl(aq) + H2O(l) MgO(s) + 2HCl(aq) MgCl2(aq) + H2O(l)

Forms Al3+ (aq) Al2O3(s) + 6HCl(aq) 2AlCl3(aq) + 3 H2O(l)

No reaction

Reaction with alkali*

No reaction White ppt dissolves in excess NaOH to form colorless complex, Al(OH)4

-

(aq) Al2O3(s) + 3H2O(l) + 2NaOH(aq) 2NaAl(OH)4(aq)

Reacts with conc. NaOH to form Na2SiO3 (aq) SiO2(s) + 2NaOH(aq) Na2SiO3(aq) + H2O(l)

Forms salt and water

P4O6(s) + 12 NaOH(aq) 4 Na3PO3(aq) + 6 H2O(l) P4O10(s) + 12 NaOH(aq) 4 Na3PO4(aq) + 6 H2O(l) SO2(g) + 2 NaOH(aq) Na2SO3(aq) + H2O(l) SO3(g) + 2 NaOH(aq) Na2SO4(aq) + H2O(l)

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Melting Points of Period 3 oxidespH of resulting solution when

Period 3 oxides react with water

7

13

2

Graph 7 Graph 8

pH of solution

7

0Na Mg Al Si P S

oxides

chlorides

pH of resulting solution when Period 3 chlorides react with water

Graph 9

©MJC 2011 6

Properties of Period 3 Chlorides

Period 3 chloride

NaCl MgCl2 AlCl3 SiCl4 PCl3, PCl5

Oxidation No.

+1 +2 +3 +4 +3, +5

Structure Giant Ionic Lattice structure

Simple molecular structure

Reaction with water*

Hydration only No hydrolysis

neutral solution

NaCl (s) +aq Na+ (aq) + Cl- (aq)

Neutral pH = 7

Slight hydrolysis slightly acidic solution MgCl2 (s) + 6H2O [Mg(H2O)6]2+ (aq) + 2Cl- (aq) [Mg(H2O)6]2+(aq) [Mg(H2O)5(OH)]+(aq) + H+(aq)

Slightly acidic pH = 6.5

Slight Hydrolysis

acidic solution

Al2Cl6(s) + 12H2O(l) 2[Al(H2O)6]3+(aq) + 6Cl-(aq) [Al(H2O)6]3+(aq) [Al(H2O)5(OH)]2+(aq) + H+(aq)

Acidic pH = 3

Complete Hydrolysis

acidic solution

SiCl4 + 2H2O SiO2 + 4HCl

Acidic pH = 2

Complete Hydrolysis

acidic solution PCl3 + 3H2O H3PO3 + 3HCl PCl5 + 4H2O H3PO4 + 5HCl

Acidic pH = 2

©MJC 2011 7