Reactions with water:
Na -> Sodium reacts very violently with water, fizzing across the surface of the water, releasing Hydrogen
gas, and producing a strong alkali solution of NaOH.
Mg ->
Magnesium reacts much more slowly with cold water, producing bubbles of Hydrogen gas and producing a
slightly alkaline solution of Mg(OH)2. However, if ignited and burnt in steam, Mg reacts very violently,
producing a white solid (MgO) along with Hydrogen gas.
Formation of the oxides:
Period 3 elements can be ignited and burnt in air to produce the relevant oxide;
Element Na Mg Al Si P S
Formula of
Oxide
Na2O MgO Al2O3 SiO2 P4O10 SO2
SO3
Equation 4Na(s) + O2(g) ->
2Na2O(s)
2Mg(s) + O2(g) ->
2MgO(s)
4Al(s) + 3O2(g) –
> 2Al2O3(s)
Si(s) + O2(g) ->
SiO2(s)
P4(s) + 5O2(g) ->
P4O10(s)
S(s) + O2(g) -> SO2(g)
Observations Melts & ignites
with orange
flame, forming
white solid
Ignites & burns
with bright
white light,
forming white
solid
The fine
powder sparks
and forms a
white solid
No
observable
reaction
Yellow flame &
white fumes
formed. White
misty fumes
collect to form
Yellow solid melts
into brown liquid
& ignites with
pale blue flame.
White misty
Bonding Ionic Ionic Ionic Covalent Covalent Covalent
Structure Giant ionic Giant ionic Giant ionic Giant
covalent
Simple
molecular
Simple
molecular
Aluminium is described as an amphoteric molecule. This means that although it is Ionic in structure, it does
indeed have covalent character, so reacts with both acids and bases.
Structure of the oxides:
Metallic oxides consist of a giant ionic lattice, with strong electrostatic forces of attraction between
oppositely charged ions, giving them high MP/BP. To prove an oxide is ionic, melt it and see if it will
conduct charge, if it does it is ionic as the ions are now free to move & carry the charge.
SiO2 is giant covalent (macromolecular). This means that every Si atom is bonded to 2 Oxygen atoms and
vice versa. As there are strong covalent bonds between all the atoms, this requires a significant amount of
energy to overcome, so has the highest MP/BP of all the oxides (also insoluble & don’t conduct electricity).
P4O10 and both sulfur oxides are simple molecular. This means there are strong covalent bonds between
the atoms, but only weak VDW’s forces between molecules. This results in a low BP/MP which is
determined by the size of the molecule (P4O10 has higher BP/MP as it is a larger molecule so has more
electrons).
Reactions of the oxides with water:
Aluminium and Silicon oxides do not react with water at all, so the result is a pH of 7 and no reaction.
The metallic oxides are basic, so react with water to produce alkaline solutions;
Na2O -> White solid reacts rapidly to form a colourless solution of NaOH and Hydrogen gas (pH 14)
MgO -> White solid reacts slowly with some dissolving to form a colourless solution of Mg(OH)2 and
Hydrogen gas (pH 9)
The non-metallic oxides are acidic, so react with water to produce acidic solutions;
P4O10 -> White solid reacts rapidly to form a colourless solution of H3PO4 (pH 2)
SO2/3 -> Both react with water to form colourless solutions of H2SO3 & H2SO4 (pH 5 and pH 3)
Reactions of the oxides with acids and bases:
Metal oxides are basic so react with acids. Non-metal oxides are acidic so react with bases. Aluminium
oxide is amphoteric, so reacts with both acids and bases;
Oxide Reaction with dilute HCl Reaction with dilute NaOH
Na2O Na2O + 2HCl -> 2NaCl + H2O N/A
MgO MgO + 2HCl -> MgCl2 + H2O N/A
Al2O3 Al2O3 + 6HCl -> 2AlCl3 + 3H2O Al2O3 + 2NaOH + 3H2O -> 2NaAl(OH)4
SiO2 N/A SiO2 + 2NaOH -> Na2SiO3 + H2O
P4O10 N/A P4O10 + 12NaOH -> 4Na3PO4 + 6H2O
SO2 N/A SO2 + 2NaOH -> Na2SO3 + H2O
SO3 N/A SO3 + 2NaOH -> Na2SO4 + H2O
Notice how water is always formed except in the reaction of Aluminium Oxide with NaOH