Period 3 Elements and Oxides

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  • Created by: Kate
  • Created on: 20-11-14 14:46
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  • Period 3 Elements and Oxides
    • Formula of Oxides
      • MgO
      • Na2O
      • Al2O3
      • SiO2
      • P4O10
      • SO3
      • SO2
    • Observations when heated with oxygen.
      • Mg
        • Burns with a bright white flame
      • Na
        • Burns with a yellow flame
        • 2Na (s) + 1/2O2 (g) => Na2O (s)
      • Al
        • Al powder burns brightly to give a white powder
        • 4Al (s) + 3O2 (g) => 2Al2O3 (s)
      • Si
        • Will always form oxide when heated strongly in oxygen
        • Si (s) + O2 (g) => Si02 (s)
      • P
        • 2 allotropes of P: Red and White Red: must be heated before it will react with oxygen White: spontaneously ignites, white smoke is observed
        • 4P (s) + 5O2 (g) => P4O10 (s)
      • S
        • Burns with a blue flame, colour gas (of sulphur dioxide) given off and a little sulphur trioxide
        • S (s) + O2 (g) => SO2 (g)
    • Bonding within the Oxide
      • Metal Oxides
        • Na, Mg, Al are examples of compounds formed by metal and non-metals. Giant ionic lattices are formed, this gives them a high melting point.
        • Al2O3 is ionic but has covalent character, because it forms a small ion with a large +ve charge, meaning O2- can distort it's electron cloud, adding covalent character.
        • Ionic character is possible to predict, if we consider the differences in electronegativity between the two atoms. Big difference =  great ionic character.
      • Non-Metal Oxides
        • Si
          • This forms a giant covalent structure (macromolecule) pushing up the melting point because of the strong covalent bonds that have to be broken in order to melt the structure
        • P and S
          • Exist as seperately covalently bonded molecules
            • P oxides exist as solids. Intermolecular forces and weak dipole dipole attraction give the structure low melting points
            • Sulphur dioxide and trioxide are gases at 298K
    • Reaction of oxides with water
      • Basic oxides
        • Na: this gives sodium hydroxide solution which is strongly alkali Na2O (s) + H2O (l) => 2Na+ (aq) + 2OH- (aq) pH: 14
        • Mg: this gives magnesium hydroxide which is sparingly soluable in water MgO (s) + H2O (l) => Mg(OH)2 (s) (reversible reaction sign) Mg2+ (aq) + 2OH- (aq) pH: 9
      • Insoluble oxides
        • Al oxide and Si di-oxides
      • Acidic Oxides
        • P: P pentoxide reacts violently producing phosphoric (V) acid P4O10 (s) + 6H2O (l) => 4H3PO4 (aq) H3PO4 ionises into H+ and H2PO4- (aq)
        • Sulphur di-oxide: reacts to give an acidic solution sulphuric (IV) acid (sulfurous acid) partially dissociates SO2 (g) + H2O (l) => H2SO3 (aq) H2SO3 (aq) (reversible reaction sign) H+ (aq) + HSO3- (aq)
        • Sulfur Trioxide: Reacts violently to produce sulfuric (VI)acid SO3 (g) +H2O (l) => H2SO4 (aq) => H+ (aq) + HSO4- (aq) pH  0-1
    • Reaction Na and Mg with water
      • Na: Vigorous reaction, sodium floats on surface of water, fizzing rapidly 2Na (s) + 2H2O (l) => 2naOH(aq)+ H2 (g)
      • Melting Points
    • Equations
      • Acidic Oxides with alkali
        • Phosphorus pentoxide: this is really the reaction of phosphorus (v) acid as this is formed when phosphorus reacts with water. This reacts in 3 separate stages, as each hydrogen reacts with a hydroxide ion and is replaced by a sodium ion. Overall: 3NaOH (aq) + H3PO4 (aq) => Na3PO4 (aq) + 3H2O (l)
        • Sulfur dioxide: this is a two stage process first forming sodium hydrogensulfate (IV): SO2 (aq) + NaOH (aq) => NaHSO3 (aq) Followed by sodium sulfate (IV): NaHSO3 (aq) + NaOH (aq) => Na2SO3 (aq) + H2O (l)
      • Basic Oxides with acid
        • Na: Reacts to give salt and water Na2O(s) + H2SO4 (aq) => Na2SO4(aq) + H2O(l) Sodium Sulfate is formed.
        • Mg: Salt and water MgO(s) + 2HCl (Aq) => MgCl2 (aq) + H2O(l)
      • Amphoteric Oxide with alkali/acid
        • Aluminium oxide reacts with both acid: Al2O3 (s) + 6HCl (aq) => 2AlCl3 (aq) + 3H2O forming aluminium chloride. Alkali: Al2O3 (s) + 2NaOH (aq) + 3H2O (l) => 2NaAl(OH)4 (aq) forming sodium aluminate


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