C22 periodicity

• in period 3, Na, Mg and Al are metals, so conduct electricity and react with acids
• in period 3, Si is a semi-metal, so conducts electricity to some extent
• in period 3, P, S and Cl are non-metals, so do not conduct electricity
• in period 3, Ar is a noble gas, so is chemically unreactive
• the reactions of the elements of period 3 are redox because all elements start with oxidation states of zero, and after reacting have a positive or negative oxidation state
• Na and Mg are the only metal elements in period 3 that react with cold water
• observations when Na reacts with water:

  • metal floats on the surface
  • rapid effervescence
  • metal melts due to heat emitted
• equation for Na reacting with water:

  2Na + 2H2O -> 2NaOH + H2
• when Na reacts with water, a strongly alkaline solution of sodium hydroxide is formed, with a pH of 13-14
• observation when Mg reacts with water:

  • very little effervescence
• equation for Mg reacting with water:

  Mg + 2H2O -> Mg(OH)2 + H2
• when Mg reacts with water, a slightly alkaline solution is formed, with a pH of 10
• the rate of the reaction of Mg with water can be increased by using heated magnesium and steam
• observation when Mg reacts with steam:

  • bright white flame
• equation for Mg reacting with steam:

  Mg + H2O -> MgO + H2
• Cl is the only non-metal element in period 3 that reacts with water
• the oxides of the period 3 elements can be prepared by reacting them directly with oxygen
• equation for production of sodium oxide:

  2Na + 1/2(O2) -> Na2O
• equation for production of magnesium oxide:

  2Mg + O2 -> 2MgO
• equation for production of aluminium oxide:

  4Al + 3O2 -> 2Al2O3
• equation for production of silicon dioxide:

  Si + O2 -> SiO2
• equation for production of phosphorus pentoxide:

  4P + 5O2 -> P4O10
• equation for production of sulfur dioxide and sulfur trioxide:

  S + O2 -> SO2 + small amount of SO3
• the oxides of Na, Mg and Al are made up of a metal and a non-metal so are compounds with ionic bonding, forming a giant ionic lattice, this gives them high melting points
• the oxide of Al has some covalent character as well as being ionic because the ion is very small and positive so can closely approach the oxygen atom and distort its electron cloud
• the oxide of Si has a macromolecular structure, so forms a giant covalent lattice, this gives it a high melting point
• the oxides of P and S have simple molecular structure, so are made up of separate covalently bonded molecules, this gives them relatively low melting points as they only have van der Waals and dipole-dipole intermolecular forces
• the order of melting points of period 3 oxides is:

  MgO > Al2O3 > SiO2 > Na2O > P4O10 > SO3 > SO2
• MgO and Na2O are both bases, so can react with water to make an alkaline solution
• equation for magnesium oxide reacting with water:

  MgO + H2O -> Mg(OH)2
• equation for sodium oxide reacting with water:

  Na2O + H2O -> 2NaOH
• sodium oxide reacting with water produces a strongly alkaline solution of sodium hydroxide with a pH of 14
• magnesium oxide reacting with water produces a slightly alkaline solution of magnesium hydroxide with a pH of 9
• Al2O3 and SiO2 are both insoluble in water
• P4O10, SO2 and SO3 are acidic, so react with water to make an acidic solution
• equation for phosphorus pentoxide reacting with water:

  P4O10 + 6H2O -> 4H3PO4
• phosphorus pentoxide reacting with water produces an acidic solution of phosphoric acid with a pH of -1 to +1
• equation for sulfur dioxide reacting with water:

  SO2 + H2O -> H2SO3
• sulfur dioxide reacting with water produces an acidic solution of sulfurous acid with a pH of 1
• equation for sulfur trioxide reacting with water:

  SO3 + H2O -> H2SO4