What are the period 3 elements?
3rd row: Na→Ar
Does aluminium oxide react with water and why?
No due to oxide layer
Is MgO or Na2O less soluble and why?
MgO less soluble due to having higher lattice enthalpy
What group is Na in?
1
How is an Na+ ion formed?
By Na losing 1 electron
What group is Mg in?
2
How is an Mg2+ ions formed?
By Mg losing 2 electrons
Is Na or Mg more reactive and why?
Na more reactive as takes less E to remove 1 electron than 2 (more E is needed for electron to react)
How does Na react with cold water?
Vigorously
Forms molten ball on surface, fizzing and H2 gas
Produces NaOH so forms strongly alkaline solution (pH 12-14)
Equation for Na reacting with cold water
2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g)
How does Mg react with cold water?
Very slowly - no visible reaction
Forms weakly alkaline solution (pH 9-10) to show reaction has occurred
Why is only a weakly alkaline solution produced when Mg reacts with cold water?
Mg(OH)2 not very soluble in water so relatively few hydroxide ions produced
Equation for Mg reacting with cold water
Mg (s) + 2H2O (l) → Mg(OH)2 (aq) + H2 (g)
Equation for Mg reacting with steam
Mg (s) + H2O (g) → MgO (s) + H2 (g)
When does Mg react faster?
Sodium oxide
Na2O
Magnesium oxide
MgO
Aluminium dioxide
Al2O3
Silicone dioxide
SiO2
Phosphorus oxide
P4O10
Sulfur dioxide
SO2
How does Na react with air?
How does Mg react with air?
How does Al react with air?
Slow
How does Si react with air?
How does P react with air?
Spontaneously combusts
How does S react with air?
Burns steadily
Colour of Na flame
Yellow
Colour of Mg flame
Brilliant white
Colour of P flame
Colour of S flame
Blue
How can you identify the elements?
Using flame tests
Equation for dissolving SO2 gas in water
SO2 (g) + H2O (l) → H2SO3 (aq) (sulphurous acid - acidic solution)
What happens when period 3 elements are reacted with oxygen?
Form oxides
What usually happens when a period 3 element reacts with O2?
Oxidised to highest oxidation state e.g Na+, Mg2+ (group no.)
What's the exception for when period 3 elements react with oxygen?
Sulfur as forms SO2 (only get +4 oxidation state)
Why is sulfur the exception when reacting period 3 elements with oxygen?
Required catalyst and high temp to get SO3 with oxidation state +6
Element+ O2 →
Oxide
2Na (s) + 1/2 O2 (g) →
Na2O (s)
Mg (s) + 1/2 O2(g) →
MgO (s)
2Al (s) + 3/2 O2 (g) →
Al2O3 (s)
Aluminium oxide
Si (s) + O2 (g) →
SiO2 (g)
P4 (s) + 5O2 (g) →
P4O10 (s)
Phosphorus (v) oxide
S (s) + O2 (g) →
SO2 (g)
Which oxides are white solids?
Phosphorus v oxide
Which oxides is a colourless gas?
SO2 (g) + 1/2 O2 (g) →←
What catalyst is used?
SO3 (g)
Vanadium (V2O5)
What’s the difference in period 3 oxides mp’s due to?
Differences in structure and bonding
Which period 3 oxides have ionic bonding?
Which period 3 oxides have giant covalent bonding?
Which period 3 oxides have simple molecular bonding?
SO3
How does the pH of oxide solutions change?
L -> R
Alkaline solution -> Acidic solution
What is the mp of the metal oxides (Na2O, MgO and Al2O3) like and why?
High mp as form giant ionic lattices - strong electrostatic forces of attraction between ions require lots of heat E to break the bonds and melt them
Which has a higher mp and why?
MgO or Na2O
MgO - Mg forms 2+ ions, which attracts O2- ions more strongly than Na+ ions
Which has a lower mp and why?
MgO or Al2O3
Al2O3 - difference in electronegativity isn’t as large as between Mg and O
Means O2- ions in Al2O3 can’t attract the e-’s in the metal-oxygen bond as strongly as in MgO - makes bonds in Al2O3 partially covalent
Which non-metal oxide has the highest mp and why?
SiO2 - has giant macromolecular structure so strong cov bonds hold structure so lots E required to break bonds and high mp
P4O10 and SO3 are _ molecules
Covalent
Describe the mp’s of P4O10 and SO3
Cov molecules so low mp as simple molecular structure
Molecules attracted to each other by weak intermolecular forces (VdWs and dipole-dipole) which take little E to overcome
How would you prove there are ions in Al2O3?
Melt Al2O3
Pass current through melted Al2O3
Ions present as will conduct
Na2O and MgO contain …
Oxide ions (O2-)
What happens when Na2O or MgO dissolves in water?
O2- ions accept protons from water molecules to form OH- ions
Form alkaline solutions
MgO and Na2O reacting with water:
Which solution will be more alkaline and why?
NaOH more alkaline than Mg(OH)2 solution as NaOH more soluble in water
Equation for MgO reacting with water:
MgO (s) + H2O (l) -> Mg(OH)2 (aq)
Equation for Na2O reacting with water:
Na2O (s) + H2O (l) -> 2NaOH (aq)
Na2O reacting with water:
What’s the pH of the resulting solution?
pH 12-14
MgO reacting with water:
pH 9-10
Simple covalent oxides and non-metal oxides form _ solutions
acidic (pH 0-1 as all acids strong)
What will happen once simple covalent oxides and non-metal oxides have reacted with water?
The acids will dissolve in water to form conjugate base
Equation for P4O10 with water:
P4O10 (s) + 6H2O -> 4H3PO4 (aq)
Equation for SO2 with water:
SO2 (g) + H2O (l) -> H2SO3 (aq)
Equation for SO3 with water:
SO3 (g) + H2O (l) -> H2SO4 (aq)
Reaction of P4O10 with water:
What acid is formed?
Phosphoric (V) acid
Reaction of SO2 with water:
Sulfurous acid
Reaction of SO3 with water:
Sulfuric (VI) acid
Dissociation of H3PO4 in water:
H3PO4 (aq) -> 3H+ (aq) + PO4 3- (aq)
Dissociation of H2SO3 in water:
H2SO3 (aq) -> 2H+ (aq) + SO3 2- (aq)
Dissociation of H2SO4 in water:
H2SO4 (aq) -> 2H+ (aq) + SO4 2- (aq)
Acid + base ->
Salt + water
What type of reaction occurs when you react an acid and base?
Neutralisation
Na2O and MgO are _ so will neutralise _
basic
acids
Na2O (s) + 2HCl (aq) ->
2NaCl (aq) + H2O (l)
MgO (s) + H2SO4 (aq) ->
MgSO4 (aq) + H20 (l)
SI, P and S oxides are _ so will neutralise _
acidic
bases
SiO2 (s) + 2 NaOH (aq) ->
Na2SiO3 (aq0 + H2O (l)
P4O10 (s) + 12NaOH (aq) ->
4Na3PO4 (aq) + H2O (l)
SO2 (g) + 2NaOH (aq) ->
Na2SO3 (aq) + H2O (l)
SO3 (g) + 2NaOH (aq) ->
Na2SO4 (aq) + H2O (l)
Al oxides are _ so will neutralise _
amphoteric
both
Al2O3 (s) + 3H2SO4 (aq) ->
Al2(SO4)3 (aq) + 3H2O (l)
Al2SO3 (s) + 2NaOH (aq) + 3H2O (l) ->
2NaAl(OH)4 (aq)
What does amphoteric mean?
Has basic and acidic properties
Is SiO2 soluble or insoluble in water and why?
Innsoluble as giant covalent
Is SiO2 acidic or basic?
Acidic as will react with bases to form salts
Is Al2O3 soluble or insoluble in water and why?
Insoluble as partially ionic, partially covalent
Is Al2O3 acidic or basic?
Amphoteric as will react with bases and acids to produce salts
What must happen for SiO2 to react with NaOH and why?
NaOH must be hot and concentrated as requires lots of E to break the cov bonds in lattice
Equations to show H3PO4 donating protons:
H3PO4 (aq) -> H+ (aq) + H2PO4 - (aq)
H2PO4 - (aq) -> H+ (aq) + HPO4 2- (aq)
HPO4 2- (aq) -> H+ (aq) + PO4 3-
Equations to show H2SO4 donating protons:
H2SO4 (aq) -> H+ (aq) + HSO4 - (aq)
HSO4 - (aq) -> H+ (aq) + SO4 2- (aq)
Equation for Al2O3 reacting with HNO3:
Al2O3 + 6HNO3 -> 2Al(NO3)3 + 3H2O
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