Chem5 - Periodicity

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Periodicity

First Ionisation Energy - The energy required to remove one mole of outer electrons from one mole of gaseous atoms.
( Mɽɡɿ → M+ɽɡɿ + e- )

Atomic Radius - The distance between the nucleus to the outer electrons.

Electronegativity - The power of an atom to attract electron density from a covalent bond. (i.e. the more electronegative something is, the stronger it attracts.

Disproportionation - When oxidation and reduction occur at the same time with the same element.
( Cl2 + H2O ↔ HCl + HClO )

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Periodicity

Reactions with Water/Steam:

2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)

Fizzing/smoke: H2 gas is produced.
Pink trail is left in the water: OH- ions produced.
Na melts: exothermic reaction.

Mg(s) + 2H2O(l) → Mg(OH)2(aq) + H2(g)
Mg(s) + H2O(l)
 → MgO(s) + H2(g)

Flame ignited at hole in test tube: H2 burning.
White powder formed: MgO produced.
Mg burned brightly: exothermic reaction. 

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Periodicity - Reactions with Oxygen

4Na(s) + O2(g)  → 2Na2O(s)
Na burns brightly with a yellow/orange flame producing white Na2O. Giant ionic lattice structure with ionic bonding due to the large electronegative difference. It has a high melting point of 1275c due to strong electrostatic forces between ions which require lots of energy.

2Mg(s) + O2(g) → 2MgO(s)
Mg burns with a bright white flame producing white MgO. Giant ionic lattice with ionic bonding. It has a higher melting point of 2852c than Na2O as Mg2+ is smaller, doubly charged and has a greater charge density. MgO has stronger electrostatic attractions

4Al(s) + 3O2(g) → 2Al2O3(s)
Al burns with a bright white flame producing white Al2O3. Giant ionic lattice with ionic bonding and some covalent character due to smaller electronegativity difference. Has a high melting point of 2072c which is greater than Na2O due to strong electrostatic attractions but less than MgO due to the 2:3 ratio of ions.

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Periodicity - Reactions with Oxygen

Si(s) + O2(g) → SiO2(s)
Si burns with a bright white flame to produce white silicon dioxide. Macromolecular/Giant covalent structure with many covalent bonds. SiO2 has a high melting point (1610c) due to many strong covalent bonds which require a high amount of energy to break.

4P(s) + 5O2(g) → P4O10(s)

White P ignites in air, burning with a white flame. White smoke of P4O10 is produced. Simple molecular structure with covalent bonding. Melting point low as Van der Waals forces need to be overcome which are weak.

S(s) + O2(g) → SO2(g)
S(yellow powder) burns with blue flame producing colourless SO2, small amts of SO3. Simple molecular, covalent bonding, Van der Waals forces and dipole attractions, melting point low (-73c) as little energy needed.

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Periodicity - Reactions of Oxides

Metal Oxides are ionic: the electronegativity difference is large.

Na2O(s) + H2O(l) → 2NaOH(aq)        (Strong alkali - fully diss. into
pH = 13-14                                                       Na+ and OH-)

Na2O + 2HCl → 2NaCl + H2O
Na2O + 2HNO3 → 2NaNO3 + H2O              (O2- + 2H+ → H2O)
Na2O + H2SO4 → Na2SO4 + H2O

MgO(s) + H2O(l) → Mg(OH)2     (Weak alkali - slightly diss. into
pH = 9-10                             Mg2+ and OH- as not very soluble)
MgO + 2HCl → MgCl2 + H2O
MgO + 2HNO3 → Mg(NO3)2 + H2O              (O2- + 2H+ → H2O)
MgO + H2SO4 → MgSO4 + H2O

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Periodicity - Reactions of Oxides

Al2O3 + H2O → INSOLUBLE

pH = 7, basic oxide
Al2O3 + 6HCl → 2AlCl3 + 3H2O 
Al2O3 + 6HNO
→ 2Al(NO3)3 + 3H2O 
Al2O3 + 3H2SO
 Al2(SO4)3 + 3H2O
Al2O3 + 2NaOH + 3H2
→ 2[Al(OH)4]- 

SiO2 + H2→ INSOLUBLE
pH = 7, acidic oxide 
SiO2(s) + 2NaOH(aq) → NaSiO3(s) + H2O(l)
 

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Periodicity - Reactions of Oxides

P4O10 + 6H2O → 4H3PO4
(strong acid, pH = 0-1)
P4O10 + 12NaOH → 4Na3PO4 + 6H2O
H3PO4 + NaOH → NaH2PO4 + H2O
NaH2PO4 + NaOH → Na2HPO4 + H2O
Na2HPO4 + NaOH → Na3PO4 + H2O
Overall: H3PO4 + 3NaOH → Na3PO4 + 3H2O

SO2 + H2O → H2SO3
(weak acid, pH = 2-3)
H2SO3 + NaOH → NaHSO3 + H2O
NaHSO3 + NaOH → Na2SO3 + H2O
Overall: H2SO3 + 2NaOH → Na2SO3 + 2H2O
SO2(g) + CaO(s) → CaSO3(s)
SO3 + H2O → H2SO4
H2SO4 + 2NaOH → Na2SO4 + 2H2O
SO3 + 2NaOH → Na2SO4 + H2O

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