periodicity Flashcards
period 3 oxides
(Na, Mg, Al, Si, P, S)
Na2O
MgO
Al2O3
SiO2
P4O10
SO3
4, 2
number of O.N. of period 3 oxides
(Na, Mg, Al, Si, P, S)
- 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
3, 1, 2
structure and bonding of period 3 oxides
(Na, Mg, Al, Si, P, S)
- 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
melting points of period 3 oxides
(Na, Mg, Al, Si, P, S)
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
2, 1, 3
acidic/basic nature of period 3 oxides
(Na, Mg, Al, Si, P, S)
- Na2O, MgO: basic
- Al2O3: amphoteric
- SiO2, P4O10, SO2: acidic
2, 2, 2
reaction with water of period 3 oxides
(Na, Mg, Al, Si, P, S)
- Na2O, MgO: dissolves in water to give alkaline solution
- Al2O3, SiO2: no reaction
- P4O10, SO2: dissolves in water to give acidic solution
Reaction with water of Na2O (period 3 oxide)
- 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)
Reaction with water of MgO (period 3 oxide)
- 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)
Reaction with water of Al2O3 (period 3 oxide)
- no reaction,
- insoluble in water due to large amount of energy needed to overcome strong ionic bonding (pH 7)
Reaction with water of SiO2 (period 3 oxide)
- no reaction,
- large amount of energy needed to overcome extensive covalent bonding (pH 7)
Reaction with water of P4O10 (period 3 oxide)
- violent reaction to
- form a fairly strongly acidic solution (pH 2)
- P4O10 (s) + 6 H2O (l) -> 4 H3PO4 (aq)
Reaction with water of SO3 (period 3 oxide)
- violent and very exothermic reaction to
- form a strongly acidic solution (pH 1)
- SO3 (l) + H2O (l) -> H2SO4 (aq)
2, 1, 3
reaction with acid/bases of period 3 oxides
(Na, Mg, Al, Si, P, S)
- 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
Reaction with acid/base of Na2O (period 3 oxide)
Na2O (s) + 2 H+ (aq) -> 2 Na+ (aq) + H2O (l)
Reaction with acid/base of MgO (period 3 oxide)
MgO (s) + 2 H+ (aq) -> Mg2+ (aq) + H2O (l)
Reaction with acid/base of Al2O3 (period 3 oxide)
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)
Reaction with acid/base of SiO2 (period 3 oxide)
- dissolves in hot and concentrated strong bases to give a colourless solution
- SiO2 (s) + 2 OH- (aq) -> SiO3 2- (aq) + H2O (l)
Reaction with acid/base of P4O10 (period 3 oxide)
- dissolves in strong bases to give a colourless solution
- P4O10 (s) + 12 OH- (aq) -> 4 PO4 3- (aq) + 6 H2O (l)
Reaction with acid/base of SO3 (period 3 oxide)
- reacts directly with bases to give a colourless solution
- SO3 (l) + 2 OH- (aq) -> SO4 2- (aq) + H2O (l)
period 3 chlorides
(Na, Mg, Al, Si, P)
NaCl
MgCl2
AlCl3
SiCl4
PCl5
2, 3
structure and bonding of period 3 chlorides
(Na, Mg, Al, Si, P)
- 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
1, 2, 2
reaction with water of period 3 chlorides
(Na, Mg, Al, Si, P)
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
Reaction with water of NaCl (period 3 chloride)
- low charge density -> will not hydrolyse in water (pH 7)
- NaCl (s) + aq -> Na+ (aq) + Cl- (aq)
Reaction with water of MgCl2 (period 3 chloride)
- 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
Reaction with water of AlCl3 (period 3 chloride)
- 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)
Reaction with water of SiCl4 (period 3 chloride)
- undergo complete hydrolysis (pH 2)
- SiCl4 (l) + 4 H2O (l) -> SiO2.2H2O (s) + 4 HCl
Reaction with water of PCl5 (period 3 chloride)
- undergo complete hydrolysis (pH 1-2)
- PCl5 (s) + 4 H2O (l) -> H3PO4 (aq) + 5 HCl (aq)
melting points of period 3 chlorides
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
thermal stability of grp 2 carbonates
- 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
reducing power of grp 2 elements
- 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
oxidising power of grp 17 elements
- 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
thermal stability of hydrogen halides (HX)
(grp 17)
- 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
description for reaction of oxides with water
- 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
- If hydroxide is very soluble,
