Sodium is more reactive than magnesium
1) sodium and magnesium are the first two elements in period 3.Sodium is in group 1 and magnesium is in group 2 . when they react sodium looses one electron and magnesium looses two electrons forming Na+ and Mg2+.
2) Sodium is more reactive than magnesium as it takes less energy to loose one electron than it does to lose two. This means magnesium requires more energy to react than sodium does.
This is shown in reactions with water.Sodium recats very vigorously with cold water forming a molten ball on the surface that fizzes and produces Hydrogen gas. Magnesium reacts slowly with cold water producing a weakly alkaline solution as MgO isnt very soluble in water and so less hydroxide ions are produced. Magnesium reacts much faster with steam to produce magnesium oxide.
2Na(s) + 2H2O(l)--------> 2NaOH(aq) + H2(g) strongly alkaline so PH= 12-14
Mg(s) + 2H2O(l)---------> Mg(OH)2 (aq) +H2(g) weakly alkaline so PH= 9-10
Sodium and Magnesium
2Na(s) + 1/2O2(g)-------> Na2O(s) sodium oxide
reaction in air is Vigorous
Mg(s) + 1/2 O2(g)--------> MgO(s) Magnesium oxide
reaction in air is Vigorous
Flame- Brilliant White
Aluminium and silicon
2Al(s) + 1.5 O2(g)---------->Al2O3(s) Aluminium Oxide
reaction in air is slow.
it doesn't produce a coloured flame.
Si(s) + O2(g)-----------> SiO2 Silicon dioxide
reaction with air - slow
It doesnt produce a coloured flame
Bonding and structure affect melting points
1) Na2O, MgO, Al2O3 - all have high melting points because they all form giant ionic lattices with strong forces of attraction between oppositely charged ions, this means more energy is required to break the bonds.
2) MgO has a higher melting point than Na2O because it forms 2+ ions so it bonds more strongly than the 1+ ions in Na2O.
3) Al2O3 has a lower melting point than you might expect because its 3+ ions distort the electron cloud making it partially covelant.
4) SiO2 has a higher melting point than the other non metal oxides as it has a giant covelant (macromolecular) structure
5) P4O10 and SO2 have relatively low melting points because they form simple molecular structures. The molecules are bound by weak intermolecular forvces (van der waal forces) which take little energy to overcome.
ionic oxides and covelant oxides
1) ionic oxides of the metals Na and Mg dissolve in water to form hydroxides which are both alkaline solutions.
2) The simple covelant oxides of the non metals phosphorous and sullphur form acidic solutions. All of the acids are strong and so the ph is about 0-2.
P4O10(s) + 6H2O --------> 4H3PO4(aq) phosphoric(V) acid
SO2(g) + H2O(l)---------> H2SO3(aq) sulphurous acid
SO3(g) + H2O(l) ----------->H2SO4(aq) sulphuric acid
3) the giant covelant structure of silicon dioxide means that it is insoluble in water. however it will react with bases to form salts so is classed as acidic.
4) Aluminium oxide, which is partially ionic and partially covelantly bonded, is also insoluble in water. It will however react with acids and bases to form salts. it can act as an acid or a base and so is classed as amphoteric.
Acid + Base----> Salt + Water
1) basic oxides neutralise acids:
Na2O +2HCl ------> 2NaCl(aq) + H2O (l)
2) Acidic oxides neutralise bases:
SiO2(s) + 2NaOH(aq)------> Na2SiO3(aq) + H2O(l)
P4O10(s) + 12NaOH(aq) ------> 4Na3PO4(aq) + 6H2O(l)
SO2(g) + 2NaOH(aq)-------> Na2SO3 (aq) + H2O(l)
SO3(g) + 2NaOH(aq)-------> Na2SO4 (aq) + H2O(l)
3) Amphoteric oxides neutralise acids and bases
Al2O3 + 3H2SO4----->Al2(SO4)3(aq) + 3H2O(l)
Al2O3(s) + 2NaOH(aq) + 3H2O(l)-------> 2NaAl(OH)4(aq)