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periodicity Flashcards

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1
Q

period 3 oxides
(Na, Mg, Al, Si, P, S)

A

Na2O
MgO
Al2O3
SiO2
P4O10
SO3

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2
Q

4, 2

number of O.N. of period 3 oxides
(Na, Mg, Al, Si, P, S)

A
  • Na, Mg, Al, Si only have 1 O.N. which corresponds to the loss of all their valence electrons
  • P and S have a wider range of O.N. as they can expand their octets (i.e. utilise their vacant d orbitals) and do not need to use all their valence electrons for bonding
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3
Q

3, 1, 2

structure and bonding of period 3 oxides
(Na, Mg, Al, Si, P, S)

A
  • Na2O, MgO, Al2O3 have giant ionic lattice structure with strong electrostatic foa bet opp-charged ions (ionic bonds)
  • SiO2 has giant molecular structure wth strong covalent bonding
  • P4O10 and SO2 are simple, discrete covalent molecules with relatively weak df bet molecules
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4
Q

melting points of period 3 oxides
(Na, Mg, Al, Si, P, S)

A

basic shape:
- Na -> higher Mg -> Al between Na and Mg -> Si between Al and Na -> lower P -> even lower S
- 1 “peak” at MgO

reason:
- Mg2+ has higher charge and smaller ionic radius
-> more exothermic /larger in magnitude L.E.
-> more energy needed to break stronger ionic bonds
- Al3+ have very high charge density
-> polarises O2- ion
-> confers covalent character to Al2O3
-> L.E> is less exothermic / smaller in magnitude than expected
-> less energy need to break ionic bonds

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5
Q

2, 1, 3

acidic/basic nature of period 3 oxides
(Na, Mg, Al, Si, P, S)

A
  • Na2O, MgO: basic
  • Al2O3: amphoteric
  • SiO2, P4O10, SO2: acidic
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6
Q

2, 2, 2

reaction with water of period 3 oxides
(Na, Mg, Al, Si, P, S)

A
  • Na2O, MgO: dissolves in water to give alkaline solution
  • Al2O3, SiO2: no reaction
  • P4O10, SO2: dissolves in water to give acidic solution
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7
Q

Reaction with water of Na2O (period 3 oxide)

A
  • vigorous and exothermic rxn,
  • dissolves completely in water to give a strongly alkaline solution (pH 13)
  • Na2O (s) + H2O (l) -> 2 Na+ (aq) + 2 OH- (aq)
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8
Q

Reaction with water of MgO (period 3 oxide)

A
  • very slow rxn,
  • limited solubility in water to form some Mg(OH)2,
  • Mg(OH)2 then dissolves partially in water to give a slightly alkaline solution (pH 9)
  • MgO (s) + H2O (l) -> Mg(OH)2 (s)
  • Mg(OH)2 (s) -> Mg 2+ (aq) + 2 OH- (aq)
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9
Q

Reaction with water of Al2O3 (period 3 oxide)

A
  • no reaction,
  • insoluble in water due to large amount of energy needed to overcome strong ionic bonding (pH 7)
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10
Q

Reaction with water of SiO2 (period 3 oxide)

A
  • no reaction,
  • large amount of energy needed to overcome extensive covalent bonding (pH 7)
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11
Q

Reaction with water of P4O10 (period 3 oxide)

A
  • violent reaction to
  • form a fairly strongly acidic solution (pH 2)
  • P4O10 (s) + 6 H2O (l) -> 4 H3PO4 (aq)
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12
Q

Reaction with water of SO3 (period 3 oxide)

A
  • violent and very exothermic reaction to
  • form a strongly acidic solution (pH 1)
  • SO3 (l) + H2O (l) -> H2SO4 (aq)
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13
Q

2, 1, 3

reaction with acid/bases of period 3 oxides
(Na, Mg, Al, Si, P, S)

A
  • Na2O, MgO: dissolves in acids to give a colourless solution
  • Al2O3: dissolves in acids and bases to give a colourless solution
  • SiO2, P4O10, SO2: dissolves in bases to give a colourless solution
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14
Q

Reaction with acid/base of Na2O (period 3 oxide)

A

Na2O (s) + 2 H+ (aq) -> 2 Na+ (aq) + H2O (l)

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15
Q

Reaction with acid/base of MgO (period 3 oxide)

A

MgO (s) + 2 H+ (aq) -> Mg2+ (aq) + H2O (l)

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16
Q

Reaction with acid/base of Al2O3 (period 3 oxide)

A

dissolves in acid and excess strong bases to give a colourless solution
- Al2O3 (s) + 6 H+ (aq) -> 2 Al+ (aq) + 3H2O (l)
- Al2O3 (s) + 2 OH- (aq) + 3 H2O (l) -> 2 [Al(OH)4]- (aq)

17
Q

Reaction with acid/base of SiO2 (period 3 oxide)

A
  • dissolves in hot and concentrated strong bases to give a colourless solution
  • SiO2 (s) + 2 OH- (aq) -> SiO3 2- (aq) + H2O (l)
18
Q

Reaction with acid/base of P4O10 (period 3 oxide)

A
  • dissolves in strong bases to give a colourless solution
  • P4O10 (s) + 12 OH- (aq) -> 4 PO4 3- (aq) + 6 H2O (l)
19
Q

Reaction with acid/base of SO3 (period 3 oxide)

A
  • reacts directly with bases to give a colourless solution
  • SO3 (l) + 2 OH- (aq) -> SO4 2- (aq) + H2O (l)
20
Q

period 3 chlorides
(Na, Mg, Al, Si, P)

A

NaCl
MgCl2
AlCl3
SiCl4
PCl5

21
Q

2, 3

structure and bonding of period 3 chlorides
(Na, Mg, Al, Si, P)

A
  • NaCl and MgCl2: giant ionic lattice structure with relatively strong electrostatic foa bet opp-charged ions (ionic bonds)
  • AlCl3, SiCl4, PCl5: simple, discrete covalent molecules with relatively weak df bet molecules
22
Q

1, 2, 2

reaction with water of period 3 chlorides
(Na, Mg, Al, Si, P)

A

All dissolve in water to form a colourless solution
- NaCl:
no hydrolysis,
form neutral solution
- MgCl2 and AlCl3:
undergo hydrolysis,
form slightly acidic solution
- SiCl4 and PCl5:
undergo complete hydrolysis,
form acidic solution

23
Q

Reaction with water of NaCl (period 3 chloride)

A
  • low charge density -> will not hydrolyse in water (pH 7)
  • NaCl (s) + aq -> Na+ (aq) + Cl- (aq)
24
Q

Reaction with water of MgCl2 (period 3 chloride)

A
  • high charge density
    -> high polarising power
    -> distorts e- cloud on anion
    -> polarised O-H bonds
    -> produce H3O+ (pH 6.5)
  • MgCl2 (s) + aq -> Mg 2+ (aq) + 2 Cl- (aq)
  • [Mg(H2O)6] 2+ (aq) + H2O (l) -> [Mg(H2O)5(OH)]+ + H3O
25
Q

Reaction with water of AlCl3 (period 3 chloride)

A
  • high charge density
    -> high polarising power
    -> distorts e- cloud on anion
    -> polarised O-H bonds
    -> produce H3O+ (pH 3)
  • AlCl3 (s) + aq -> Al 3+ (aq) + 3 Cl- (aq)
  • [Al(H2O)6] 3+ (aq) + H2O (l) -> [Al(H2O)5(OH)] 2+ + H3O + (aq)
26
Q

Reaction with water of SiCl4 (period 3 chloride)

A
  • undergo complete hydrolysis (pH 2)
  • SiCl4 (l) + 4 H2O (l) -> SiO2.2H2O (s) + 4 HCl
27
Q

Reaction with water of PCl5 (period 3 chloride)

A
  • undergo complete hydrolysis (pH 1-2)
  • PCl5 (s) + 4 H2O (l) -> H3PO4 (aq) + 5 HCl (aq)
28
Q

melting points of period 3 chlorides

A

shape:
NaCl -> higher MgCl2
-> low AlCl3 -> lower SiCl4 -> PCl5 between AlCl3 and SiCl4

reasons:
- Mg2+ has smaller ionic radius and higher charge
-> higher polarising power
-> partial covalent character
-> less exothermic / smaller in magnitude L.E.
-> less energy needed to overcome ionic bonding
- electron cloud size increases in order:
AlCl3 (forms dimer Al2Cl6) > PCl5 > SiCl4
-> polarisability of molecules increase in order
-> strength of df increase in order
-> amt of energy needed to overcome df increase in order

29
Q

thermal stability of grp 2 carbonates

A
  • eqn: MCO(s) -> MO (s) + CO2 (g)
  • trend: decreases down the grp
    • cationic radius increases with charge remaining constant
    • charge density and polarising power decreases
    • effect of distortion of electron cloud of anion by cation and the weakening of C-O bond decreases
    • energy and temp needed for thermal decomposition decreases
30
Q

reducing power of grp 2 elements

A
  • trend: increases down the grp
    • atomic radii increase
    • weaker electrostatic f.o.a. between nucleus and valence e-
    • metal atoms lose their valence e- to form cations more easily
    • increasing tendency to be oxidised
31
Q

oxidising power of grp 17 elements

A
  • trend: decreases down the group
    • atomic radii increases
    • weaker electrostatic f.o.a. between nucleus and valence e-
    • metal atoms unable to gain electrons to form anion as easily
    • decreasing tendency to be reduced
32
Q

thermal stability of hydrogen halides (HX)
(grp 17)

A
  • trend: decreases down the group
    • atomic radii increases
    • extent of overlap between H and X atoms decreases
    • bond length increases and bond strength decreases
    • less energy needed to break the bond
33
Q

description for reaction of oxides with water

A
  • Descriptors:
    • speed of reaction
    • solubility of hydroxide formed
    • (if applicable) exothermic rxn
  • If oxide is a known period 3 oxide, just describe according to knowledge
  • If oxide is unknown oxide, can infer description of reaction through info given on solubility of its hydroxide
    (e.g Ca(OH)2 has higher solubility (0.025 mol dm-3) than Mg(OH)2 (0.00016 mol dm-3))
    • If hydroxide is very soluble,
      • fast reaction (e.g CaO reacts rapidly with water)
      • soluble hydroxide (e.g. to give aq Ca(OH)2)
      • exothermic reaction

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