Period 3

Trends in the reactions of the elements with water, limited to Na and Mg Sodium reacts with cold water. It fizzes around on surface etc. 2 Na (s) + 2 H2O (l)
2 NaOH (aq) + H2 (g) Learn the equations Magnesium reacts very slowly with cold water to form the hydroxide but reacts more readily with steam to form the oxide Mg (s) + H2O (g)
MgO (s) + H2 (g) Trends in the reactions of the elements Na, Mg, Al, Si, P and S with oxygen The elements all react with oxygen to form oxides. Sodium burns with a yellow flame to produce a white solid Mg, Al, Si and P burn with a white flame to give white solid smoke S burns with a blue flame to form an acidic choking gas. 4 Na (s) + O2 (g)
2 Na2O (s) 2Mg (s) + O2 (g)
2MgO (s) 4Al + 3O2 (g)
2Al2O3 (s) Si + O2 (g)
SiO2 (s) 4P + 5O2 (g)
P4O10 (s) S+ O2 (g)
SO2 (g) You should be able to write these equations. Learn the formulae of the oxides Sodium is stored under oil and phosphorus under water to stop these elements coming into contact and reacting with air

A survey of the properties of the oxides of Period 3 elements Understand the link between the physical properties of the highest oxides of the elements Na
S and their structure and bonding. Ionic oxides The metal oxides (Na2O, MgO, Al2O3 ) are ionic. They have high melting points. They have Ionic giant lattice structures: strong forces of attraction between ions : higher mp. They are ionic because of the large electronegativity difference between metal and O The increased charge on the cation makes the ionic forces stronger (bigger lattice enthalpies of dissociation) going from Na to Al so leading to increasing melting points. Al2O3 is ionic but does show some covalent character. This can be explained by the electronegativity difference being less big or alternatively by the small aluminium ion with a high charge being able to get close to the oxide ion and distorting the oxide charge cloud Macromolecular oxides SiO2 is Macromolecular: It has many very strong covalent bonds between atoms. High energy needed to break the many strong covalent bonds – very high mp +bp Simple molecular oxides: P4O10 (s), SO2 (g) are simple molecular with weak intermolecular forces between molecules (van der waals + permanent dipoles) so have lower mp’s. They are covalent because of the small electronegativity difference between the non-metal and O atoms. P4O10 is a molecule containing 4P’s and 10 O’s. As it is a bigger molecule and has more electrons than SO2 it will have larger van der waals forces and a higher melting point. To prove that the above compounds contain ions experimentally – melt the solids and show they conduct electricity Aluminium metal is protected from corrosion in moist air by a thin layer of aluminium oxide. The high lattice strength of aluminium oxide and its insolubility in water make this layer impermeable to air and water

The reactions of the oxides of the elements Na
S with water know the change in pH of the resulting solutions across the Period. Metal ionic oxides tend to react with water to form hydroxides which are alkaline Na2O (s) + H2O (l)
2Na+ (aq) + 2OH- (aq) pH 13 (This is a vigorous exothermic reaction) The ionic oxides are basic as the oxide ions accept protons to become hydroxide ions in this reaction (acting as a bronsted lowry base) MgO (s) + H2O (l)
Mg(OH)2 (s) pH 9 Mg(OH)2 is only slightly soluble in water as its lattice is stronger so fewer free OHions are produced and so lower pH Al2O3 and SiO2 do not dissolve in water because of the high strength of the Al2O3 ionic lattice and the SiO2 macromolecular structure, so they give a neutral pH 7 The non-metal, simple molecular, covalent, oxides react with water to give acids P4O10 (s) + 6 H2O (l)
4 H3PO4 (aq) pH 0 (this is a vigorous exothermic reaction) SO2 (g) + H2O (l)
H2SO3 (aq) pH 3 (weak acid) SO3 (g) + H2O (l)
H2SO4 (aq) pH 0 Learn the equations ! The trend is the ionic metal oxides show basic behaviour and the non-metal covalent oxides show acidic behaviour. The slightly intermediate nature of the bonding in Aluminium oxide is reflected in its amphoteric behaviour: it can act as both a base and an acid MgO is better than NaOH for treating acid in rivers and the stomach as it is only sparingly soluble and weakly alkaline so using an excess would not make the water excessively alkaline. N Goalby chemrevise.org SO2 + H2O
H+ + HSO3 – SO3 + H2O
H+ + HSO4 – Equations showing formation of ions in solution

Acid base reactions between period 3 oxides and simple acids and bases. The basic oxides react with acids to make salts Na2O (s) + 2 HCl (aq)
2NaCl (aq) + H2O (l) Na2O (s) + H2SO4 (aq)
Na2SO4 (aq) + H2O (l) MgO (s) + 2 HCl (aq)
MgCl2 (aq) + H2O (l) Or ionically Na2O (s) + 2H+ (aq)
2Na+ (aq) + H2O (l) MgO (s) + 2 H+ (aq)
Mg2+ (aq) + H2O (l) Rather than learning the equations by rote, learn the pattern. Most follow the pattern acid + base = salt + water Know the charges on the ions e.g. PO4 3- , SO4 2- Amphoteric Oxides Aluminium oxide can act as both an acid and an alkali and is therefore called amphoteric Aluminum oxide acting as a base Al2O3 (s)+ 3H2SO4 (aq)
Al2 (SO4 )3 (aq) + 3H2O (l) Al2O3 + 6HCl
2AlCl3 + 3H2O Or ionically Al2O3 + 6H+
2Al3+ + 3H2O Aluminum oxide acting as a acid Al2O3 (s)+ 2NaOH (aq) + 3H2O (l)
2NaAl(OH)4 (aq) (this equation needs learning carefully) Al2O3 (s)+ 2OH- (aq) + 3H2O (l)
2Al(OH)4 – (aq) SiO2 has a giant covalent structure with very strong bonds. This stops SiO2 dissolving or reacting with water and weak solutions of alkali. It will, however, react with very concentrated NaOH 2NaOH (l) + SiO2 (s)
Na2SiO3 (aq) + H2O It is still classed as an acidic oxide The other simple molecular acidic oxides react with bases to form salts. P4O10 (s) + 12 NaOH (aq)
4Na3PO4 (aq) + 6 H2O (l) P4O10 + 6 Na2O
4Na3PO4 SO2 (g) + 2NaOH (aq)
Na2SO3 (aq) + H2O (l) SO3 (g) + 2NaOH(aq)
Na2SO4 (aq) + H2O (l) Or show ionically P4O10 (s) + 12 OH- (aq)
4PO4 3-(aq) + 6 H2O (l) SO2 (g) + 2OH- (aq)
SO3 2- (aq) + H2O (l) SO3 (g) + 2OH- (aq)
SO4 2- (aq) + H2O (l) Be careful for whether the question is asking for an ionic equation or a full one