H2 Chem Summary of Chemical Periodicity

Meridian Junior College

Summary of Periodic Table - Chemical Periodicity

Physical Properties of Period 3 Element Period 3 element Atomic No. Atomic Radius Graph 1 Ionic Radius Graph 2 Melting pt

Na 11

Mg 12

Al 13

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

Graph 5

Electronegativity Graph 6

©MJC 2011

P 15

S 16

Cl 17

Ar 18

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

Graph 3

Electrical conductivity Graph 4 First I.E

Si 14

Highest m.p. due to macromolecular structure. Numerous covalent bonds between Si atoms arranged tetrahedrally in a 3Dimensional structure. Low electrical conductivity as Si is a metalloid

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

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

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

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

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Summary of Trends exhibited by Elements across Period 3 Atomic radius / nm

Ionic radius /nm

Graph 1

Graph 2

Graph 5 first

P3-

S2-

Cl-

Na+ Mg2+

Al3+ 4+

Si

Proton number Na Mg Al Na

Mg Al

Si

P

S

Cl

Si

P

S

Proton number

Cl

Ar Electrical conductivity

Graph 3

Na Mg Al

©MJC 2011

Graph 6

Graph 4

Si

P

S

Cl

Ar

Proton number

2

Chemical Properties of Period 3 Element Period 3 element Reaction with dry O2*

Na Very vigorous

Mg Very vigorous

Burns with yellow flame

Burns with bright white flame

2Na (s) + ½O2 (g)  Na2O (s)

Reaction with dry Cl2*

Mg (s) + ½O2 (g)  MgO (s)

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

Si Slow Needs to be strongly heated Si(s) + O2 (g)  SiO2 (s)

P Vigorous

S Slow

Cl ---

Ar ---

---

---

Burns with a blue flame

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

With excess O2, SO2 is oxidised to SO3

P4(s) + 5O2 (g)  P4O10 (s)

S(s) + O2 (g)  SO2 (g)

Slow

Very vigorous

Vigorous

Vigorous

Slow

Slow

Na (s) + Cl2 (g)  2NaCl (s)

Mg(s) + Cl2 (g)  MgCl2 (s)

2Al(s) + 3Cl2 (g)  Al2Cl6 (s)

Si (s) + 2Cl2 (g)  SiCl4 (l)

2 chlorides (PCl3 & PCl5) formed

(Not required in syllabus)

PCl5 formed in excess Cl2 P4(s) + 6Cl2 (g)  4 PCl3 (s) P4(s) +10Cl2 (g)  4 PCl5 (s)

Reaction with cold water*

Reacts vigorously with water to form hydroxide & H2(g)

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

Al reacts with steam.

No reaction

2 Al(s) + 3 H2O (g)  Al2O3 (s) + 3 H2

2 Na (s) + 2 H2O  2NaOH(aq) + H2 (g)

©MJC 2011

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Properties of Period 3 Oxides Period 3 oxide Oxidation No.

Na2O

MgO

Al2O3

SiO2

P4O6, P4O10

SO2, SO3

+1

+2

+3

+4

+3, +5

+4, +6

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

Structure Nature of Oxide Reaction with water*

Giant Ionic Lattice Structure Ionic & basic Forms NaOH with water (pH ≈ 13)

Forms Mg(OH)2 with boiling water (pH ≈ 9)

Giant molecular Structure

Ionic & amphoteric

Simple molecular Structure Covalent & acidic

No reaction (pH = 7)

Form H3PO3, H3PO4 with water

Form H2SO3, H2SO4 with water

(pH ≈ 2)

(pH ≈ 2)

Na2O(s) + H2O(l) MgO (s) + H2O(l) Al2O3 does not dissolve in water because of P4O6(s) + 6H2O(l)  4H3PO3(aq) → 2NaOH(aq) Mg2+ (aq) + its extremely high lattice energy 2OH (aq)

SiO2

- Large amounts of energy are required to break the numerous strong covalent bonds, solvation cannot occur.

Reaction with acid*

Form salt and water Na2O(s) + 2HCl(aq)  2NaCl(aq) + H2O(l) MgO(s) + 2HCl(aq)  MgCl2(aq) + H2O(l)

Reaction with alkali*

No reaction

Forms Al3+ (aq)

SO3(g) + H2O(l)  H2SO4(aq)

No reaction

Al2O3(s) + 6HCl(aq)  2AlCl3(aq) + 3 H2O(l) White ppt dissolves in excess NaOH to form colorless complex, Al(OH)4 (aq) Al2O3(s) + 3H2O(l) + 2NaOH(aq)  2NaAl(OH)4(aq)

©MJC 2011

P4O10(s) + 6H2O(l)  4H3PO4(aq)

SO2(g) + H2O(l)  H2SO3(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)

4

pH of resulting solution when Period 3 oxides react with water

Melting Points of Period 3 oxides

Graph 7

Graph 8 13

7

2

pH of resulting solution when Period 3 chlorides react with water

pH of solution

Graph 9 oxides 7

chlorides

0

©MJC 2011

Na

Mg

Al

Si

P

S

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Properties of Period 3 Chlorides Period 3 chloride Oxidation No. Structure

NaCl

MgCl2

AlCl3

SiCl4

PCl3, PCl5

+1

+2

+3

+4

+3, +5

Reaction with water*

Hydration only No hydrolysis

Giant Ionic Lattice structure

neutral solution NaCl (s) +aq  Na+ (aq) + Cl- (aq)

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)

Neutral pH = 7

©MJC 2011

Slightly acidic pH = 6.5

Simple molecular structure Slight Hydrolysis

Complete Hydrolysis

Complete Hydrolysis

acidic solution

acidic solution

acidic solution

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

SiCl4 + 2H2O  SiO2 + 4HCl

[Al(H2O)6]3+(aq)  [Al(H2O)5(OH)]2+(aq) + H+(aq)

Acidic pH = 3

Acidic pH = 2

PCl3 + 3H2O  H3PO3 + 3HCl PCl5 + 4H2O  H3PO4 + 5HCl

Acidic pH = 2

6

©MJC 2011

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