3.2.4 Properties of Period 3 elements

• Sodium reacts with cold water. It fizzes around on the surface

  
  

  2 Na (s) + 2 H2O (l) -> 2 NaOH (aq) + H2 (g)
• Mg(OH)2 is only slightly soluble in water as its lattice is stronger.
• SiO2 does not dissolve in water due to it's macromolecular structure. pH = 7
• Aluminium is described as an amphoteric oxide because it can act both as an acid and a base
• Equation for Aluminium Oxide and Sulfuric Acid:

  
  

  Al2O3 (s)+ 3H2SO4 (aq) -> Al2(SO4)3 (aq) + 3H2O (l)
• Equation for Al2O3 and NaOH:

  
  

  Al2O3 (s)+ 2NaOH (aq) + 3H2O (l) -> 2NaAl(OH)4
• Equation for the reaction of SiO2 with NaOH:

  
  

  2NaOH + SiO2 -> Na2SiO3 + H2O
• Equation for P4O10 and Na2O:

  P4O10 + 6 Na2O -> 4Na3PO4
• In order to prove that a compound contains ions:

  • Melt the solids
  • Then show they conduct electricity
• Mg reacts with steam to produce a bright white flame and white solid / powder
• SiO2 has a lower melting point than Al2O3 because covalent bonding is weaker in SiO2-
• Reaction of sodium with acid:

  
  

  Na + acid → H2 + salt
• Reaction of sodium with oxygen:

  Bright yellow flame

  forms white powder of Na2O 2Na + ½ O2 → Na2O
• Magnesium properties:

  • Metallic
  • Shiny
  • Conducts electricity (between Na and Al in terms of how well it does).
• Reaction of Mg with oxygen:

  Bright white flame, forms white powder of MgO 2Mg + O2 → 2MgO
• What is the best conductor of electricity in period 3? Aluminium
• Does aluminium react with cold water?

  No
• Reaction of Al with oxygen:

  • Heat and lower into jar of O2
  • → bright flame, forms white powder.
  • 4Al + 3O2 → 2Al2O3
• Aluminium is considered unreactive even though the metal itself is reactive because:

  it is covered by Al2O3 from where oxygen has oxidised the surface of the Al.
• Appearance and physical properties of silicon:

  • Semimetal (metalloid)
  • semiconductor (conducts electricity to an extent and in certain conditions)
• Reaction of silicon with oxygen:

  • Heat strongly
  • Si + O2 → SiO2 (white powder)
• What are the different types of structure and bonding displayed by the period 3 oxides?

  • Na ionic lattice
  • Mg ionic lattice
  • Al ionic lattice with covalent character Al3 + distorts O2 - electron cloud
  • Si giant covalent
  • P simple molecular covalent
  • S simple molecular covalent
• Which period 3 oxides are basic? Na2O and MgO
• Reaction of Na oxide with water:

  
  

  Na2O + H2O → 2Na+ + 2OH- ; pH = 14
• Is aluminium oxide acidic or basic? It is amphoteric
• Is silicon dioxide soluble in water? No
• How is silicon dioxide used in the production of Fe? SiO2 + CaO → CaSiO3 - calcium silicate
• Reaction of SO2 with water? pH?

  SO2 + H2O → H2SO3 ; weak acid → pH = 2 - 3
• How can flue gases be removed by CaO?

  
  

  CaO + SO2 → CaSO3 (calcium sulfite)
• How many electrons does P have in its outer shell in H3PO4 ? 10
• Label the structure of H3PO4

  A) O

  B) P

  C) O

  D) H