periodicty rxns

• Periodicity of chemical properties


  Refers to the periodic variation in the chemical properties of elements as you move across the periodic table
• Reactions of elements with oxygen


  • Reaction with oxygen
  • Reaction with water
  • Reaction with chlorine
• Reaction with oxygen


  2Na (s) + O2 (g) -> Na2O (s)
• Sodium oxide (Na2O)


  • Bright yellow flame
  • White solid
  • Vigorous reaction
• Sodium oxide + water


  Na2O (s) + H2O (l) -> 2NaOH (aq)
• Sodium hydroxide (NaOH)


  • Strong alkali
• Sodium oxide is a basic oxide with a giant ionic structure
• Reaction of magnesium with oxygen


  Mg (s) + O2 (g) -> MgO (s)
• Magnesium oxide (MgO)


  • Bright white flame
  • White solid
  • Vigorous reaction
• Magnesium oxide + water

  MgO (s) + H2O (l) -> Mg(OH)2 (aq)
• Magnesium hydroxide (Mg(OH)2)


  • Weak alkali
• MgO and Mg(OH)2 are used to treat indigestion by neutralizing excess acid in the stomach
• Reaction of hydrochloric acid and magnesium oxide

  2HCl (aq) + MgO (s) -> MgCl2 (aq) + H2O (l)
• Reaction of aluminium with oxygen

  2Al (s) + 3O2 (g) -> Al2O3 (s)
• Aluminium oxide (Al2O3)


  • Bright white flame
  • White solid
  • Slow reaction
• Aluminium metal has a protective oxide layer that is non-porous, so the reaction only occurs when this layer is scraped off
• Al2O3 does not dissolve in water
• Amphoteric


  Able to react with both acids and bases
• Reaction of aluminium oxide with sulfuric acid


  Al2O3 (s) + 3H2SO4 (aq) -> Al2(SO4)3 (aq) + 3H2O (l)
• Reaction of aluminium oxide with sodium hydroxide

  Al2O3 (s) + 2NaOH (aq) + 3H2O (l) -> 2NaAl(OH)4 (aq)
• Al2O3 is used to make ceramics due to its giant ionic structure and ability to withstand high temperatures
• Reaction of silicon with oxygen


  Si (s) + O2 (g) -> SiO2 (s)
• Silicon dioxide (SiO2)


  • Slow reaction
  • Giant molecular structure
  • Insoluble in water
• SiO2 is classified as an acidic oxide
• Reaction of silicon dioxide with sodium hydroxide

  SiO2 (s) + 2NaOH (aq) -> Na2SiO3 (aq) + H2O (l)
• Reaction of sulfur with oxygen

  S (s) + O2 (g) -> SO2 (g)
• Sulfur dioxide (SO2)


  • Blue flame
• Oxidation of sulfur dioxide

  SO2 (g) + 1/2O2 (g) -> SO3 (g)
• Both SO2 and SO3 are acidic gases that dissolve in water to form acidic solutions
• Reaction of phosphorus with oxygen


  4P (s) + 5O2 (g) -> 2P4O10 (s)
• Phosphorus pentoxide (P4O10)


  • Clouds of white solid
  • Acidic oxide
• Reaction of phosphorus pentoxide with water

  P4O10 (s) + 6H2O (l) -> 4H3PO4 (aq)
• Chlorine and argon do not react with oxygen
• Summary of properties of oxides


  • Na2O (basic)
  • MgO (basic)
  • Al2O3 (amphoteric)
  • SiO2 (acidic)
  • P4O10 (acidic)
  • SO2/SO3 (acidic)
  • Cl2O7 (acidic)
• As we move across period 3, the nature of oxides gradually changes from basic to amphoteric to acidic
• Electronegativity


  The ability of an element to pull the electron cloud towards itself in a covalent bond
• Electronegativity increases as we move from left to right in the periodic table
• This is because as atomic number increases, proton number increases, leading to a stronger nuclear charge that can more strongly attract the valence electrons</b>
• Increasing electronegativity difference


  Leads to greater ionicity of the compound
• Na2O and MgO are purely ionic due to the large electronegativity difference