2.3 period 3 elements Flashcards
reaction of sodium with water
loses one electron to form Na+
reacts vigorously with cold water to form molten ball on surface, fizzing and producing H2 gas
2Na(s) + 2H2O(l) -> 2NaOH(aq) + H2(g)
reaction of magnesium with water
loses 2 electrons to form Mg2+
reacts very slowly with cold water
cant see any reaction but forms weakly alkaline solution
Mg(s) + 2H2O(l) -> Mg(OH)2(aq) + H2(g)
only weakly alkaline as Mg(OH)2 isnt very soluble in water so few OH ions produced
reaction of magnesium with steam
much faster than with water
Mg(s) + H2O(g) -> MgO(s) + H2(g)
reactions of period 3 elements with oxygen
form oxides
usually oxidised to highest oxidation state- same as group number
exception is sulphur- forms SO2 where is has +4 oxidation state (higher temp and catalyst needed to make SO3 where it has oxidation state of +6)
sodium + oxygen
2Na(s) + 1/2O2(g) -> Na2O(s)
magnesium + oxygen
Mg(s) + 1/2O2 -> MgO(s)
aluminium + oxygen
2Al(s) + 1 1/2O2(g) -> Al2O3(s)
silicon + oxygen
Si(s) + O2(g) -> SiO2(s)
phosphorus + oxygen
P4(s) + 5O2(g) -> P4O10(s) (phosphorus V oxide)
sulfur + oxygen
S(s) + O2(g) -> SO2(g) (sulfur dioxide)
reaction of period 3 elements in air
Na- Na2O- vigorous- yellow flame
Mg- MgO- vigorous- brilliant white flame
Al- Al2O3- slow- N/A
Si- SiO2- slow- N/A
P- P4O10- spontaneously combusts- brilliant white flame
S- SO2- burns steadily- blue flame
graph of melting points of period 3 oxides
page 126 of text book
why do Na2O, MgO and Al2O3 have high melting points?
they form giant ionic lattices
strong forces of attraction between each ion takes lots of energy to break bonds
why does Al2O3 have lower mp than expected?
diff in electronegativity between Al and O isnt as big as between Mg and O so O2- ions in Al2O3 cant attract electrons in metal-oxygen bond as strongly as in MgO
Makes the bonds in AL2O3 partially covalent
why does MgO have a higher mp than Na2O?
Mg forms Mg2+ ions which attracts O2- more strongly than the 1+ Na ions
why does SiO2 have a higher mp than the other non-metal oxides?
giant macromolecular structure
strong covalent bonds take lots of energy to break
why do P4O10 and SO3 have relatively low mps?
simple covalent molecules
weak intermolecular forces take little energy to overcome
reactions of period 3 oxides with water
Na2O + H2O -> 2NaOH pH=14
MgO + H2O -> Mg(OH)2 pH= 9-10
Al2O3 and SiO2 dont react/dissolve in H2O
P4O10 + 6H2O -> 4H3PO4 pH= 1-2
SO2 + H2O -> H2SO3 pH= 2-3
SO3 + H2O -> H2SO4 pH= 0-1
what does amphoteric mean?
can act as an acid or base
eg Al2O3
reactions of period 3 oxides with acids and bases
bases:
Na2O + 2HCl -> 2NaCl + H2O
MgO + H2SO4 -> MgSO4 + H2O
acids:
SiO2 + 2NaOH -> Na2SiO3 + H2O
P4O10 + 12NaOH -> 4Na3PO4 + 6H2O
SO2 + 2NaOH -> Na2SO3 + H2O
SO3 + 2NaOH -> Na2SO4 + H2O
amphoteric:
Al2O3 + 3H2SO4 -> Al2(SO4)3 + 3H2O
Al2O3 + 2NaOH + 3H2O -> 2NaAl(OH)4
observations of sodium with oxygen
yellow flame
white solid
