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)
equation for reaction of period 3 elements and oxygen
element(s) + oxygen(g) -> oxide(s)
page 125 of text book for exact equations
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
ionic oxides of Na and Mg contain O^2-. When they dissolve in water, O^2- ions accept proton from water molecules to form hydroxide ions. Solutions are both alkaline but NaOH is more soluble in water so forms more alkaline solution than Mg(OH)2
Na2O + H2O -> 2NaOH
MgO + H2O -> Mg(OH)2
simple covalent oxides of P and S form acidic solutions. strong. dissociate to form conjugate base
SiO2 is insoluble in water but reacts w bases to form salts so classed as acidic
aluminium oxide is partially covalent and partially ionic and is insoluble in water. reacts w acids and bases to form salts- amphoteric
what does amphoteric mean?
can act as an acid or base
equations for reactions of p3 oxides with water
see page 127 of text book
