properties of period 3 elements
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reactions of metallic elements with water
sodium hydrogen gas, effervesence,float,yellow flame 2Na + 2H2O = 2NaOH + H2 magnesium slower, white powder, bright white light and white flame steam= Mg + H2O = MgO + h2 WATER = Mg + 2H2O = Mg(OH2)_ + h2
reactions of non-metallic elements with water
chlorine dissolves giving very pale green solution Cl2 + H2O = HCl + HCLO
reactions of metallic elements with oxygen
sodium burns with yellow flame - produces white powder 4Na + O2 = 2Na2O magnesium burns with bright white flame and produces white powder 2Mg + O2 = 2MgO aluminium burn with white flame to produce white powder 4Al + 3O2 = 2Al2O3
reactions of non-metal with oxygen
silicon burns with white flame to produce a white powder Si + O2 = SiO2 phosphorus very bright white flame producing a white powder P4 + 5O2 = P4O10 sulfur burns with blue flame and gives off misty fumes of choking gas S + O2 = SO2
what is the overall trend in the melting points of the oxides
increase then decrease
what is the explanation for the melt points of the metallic oxides
high melting points = giant ionic lattice with strong forces of attraction bwt each ion lots of heat energy required to break the bonds
why does MgO have a higher mp than Na2O
2+ ions attract O2- ion more strongly than 1+ Na atoms -Mg smaller ion with higher charge -more energy required to break ionic bond
why is Al2O3 mp lower than expected
bc 3+ ions are small with high charge this distorts oxygen electron cloud making the bond partially covalent
non-metal mp trend
SiO2 highest of non-metals forms a macromolecular structure strong bonds that require lots of energy to be broken P4O10 & SO2 simple covalent molecules weak intermolecular forces that are VDW
why does P4O10 have a larger mp than SO2
much bigger molecule than SO2 =- therefore it has more electrons and so has greater VDW
what are the basic hydroxide metallic oxide reactions with water- goes into ions
Na2O fast reaction and dissolves into a colourless solution Na2O + H2O = 2Na+ + 2OH- ph 14 and ionic lattice strong alkali MgO sparingly soluble so few O2- MgO + H2O = Mg2+ + 2OH- weak alkali ph 10
what are the insoluble oxides
Al2O3 insoluble therefore no O2- ions the bonding is too strong so does not react with water ionic + partial covalent character ph 7 SiO2 insoluble so therefore no O2- ions giant = not soluble ph 7
what are the acidic non-metallic reactions with water
P4O10 violent reaction to give a colourless solution P4O10 + 6H2O = 4H3PO4 = phosphoric acid strong acid as fully dissociates into ions ph 0 SO2 moderately soluble SO2 + H2O = H2SO3 weak acids only partially dissociates = produces sulphuric (IV) acid or sulfurous acid ph 3 SO3 SO3 + H2O = H2SO4 strong acid as fully dissociates into sulphuric acid
what is the general ph trend across period 3
alkali to acid
what factors are involved in the reactions of the oxides with water
solubility chemical trend - the chemical trend is masked by solubility
in what situation does a substance change the ph of water
if it dissolves
write an equation for the reaction of excess magnesium oxide and phosphoric acid
3 MgO + 2 H3PO4 = Mg3(PO4)2 + 3H2O
write an ionic equation for the reaction of phosphorus oxide and sodium hydroxide
P4O10 + 12 OH- = 4PO3 ^3- + 6 H2O
what oxide of a period 3 element is amphoteric
Al2O3 -due to the fact it can react with acids and bases
give 2 equations to show the amphoteric nature of Al2O3
Acid equation Al2O3 + 6HCl = 2Al^3+ + 6Cl- + 3H2O Base equation Al2O3 + 2NaOH + 3H2O → 2Na+ + 2[Al(OH)4]-
write an equation to show the reaction bwt SiO2 and NaOH to form a neutral solution/ soluble salt and water
SiO2 (s) + 2NaOH (aq) -> NaSiO3 (aq) + H2O(l)
write an equation to show the first ionisation stage of H2SO3
H2SO3 = H+ + HSO3- -reversible reaction