Periodicity

• Periodicity = the repeating patterns/trends of the elements & their properties

  • metals & non-metals touching line dividing metals & non-metals are metalloids
  • combination of metallic & non-metallic properties
  • lanthanides normally form +3 ions
  • actinides are radioactive
• Trends in properties of elements of period 3

  melting/boiling point

  trend: decreases along the group

  • higher nuclear charge
  • shielding increases
  • atomic radius increases

  A) giant structure

  B) most van der Waals forces

  
• Trend in properties in Period 3

  1st ionisation energy

  trend: increases along the period

  • nuclear charge increases
  • atomic radius decreases
  • stronger electrostatic charge
  • same electron shielding

  A) 2-3: electron move up an orbital

  B) 5-6: electrons in orbital repel

  
• Trends in period 3

  Going left - right:

  • atomic radius DECREASES
  • electronegativity INCREASES
• Period 3 + oxygen (observations) pt1

  4Na(s)­ + O2(g) → 2Na2O(s)

  Yellow flame, white solid

  2Mg(s) + O2(g) → 2MgO(s)

  Bright white flame, white solid

  4Al(s) + 3O2(g) → 2Al2O3(s)

  white solid
• Period 3 + oxygen (observations) pt2

  Si(s) + O2(g) → SiO2(g)       

  white solid

  P4(s) + 5O2(g) → P4O10(s)   

  white solid

  S(s) + O2(g) → SO2(g)

  2S(s) + 3O2(g) → SO3(l)

  Colourless gas/liquid, burns with bright blue flame
• Period 3 oxides + water pt1

  Na2O(s) + H2O(l) → NaOH(aq)       pH = 14

  MgO(s) + H2O(l) → Mg(OH)2(aq)      pH = 9

  Al2O3(s) doesn't dissolve in water pH = 7

  SiO2(s) doesn't dissolve in water pH = 7
• Period 3 oxides + water pt2

  P4O10(s) + 6H2O(l) → 4H3PO4(aq)     pH = 0

  SO2(g) + H2O(l) → H2SO3(aq)            pH = 3 weak sulfuric(IV) acid

  SO3(l) + H2O(l) → H2SO4(aq)            pH = 0 sulfuric(VI) acid
• Properties of Period 3 oxides

  • Mg2+ has higher charge & is smaller ion compared to Na+ -> stronger electrostatic attraction to O2- -> higher MP
  • Al2O3 has covalent characteristics -> lowers MP
  • SiO2 has strong covalent bonds -> higher MP
  • P4O10/SO2/SO3 have weak IMF
  • SO3 is larger -> stronger VdW than SO2

  A) ionic

  B) ionic

  C) ionic(ish)

  D) giant covalent

  E) simple covalent

  F) simple covalent

  G) simple covalent

  H) 1500

  I) 2900

  J) 2100

  K) 1610

  L) 300

  M) -73

  N) 17

  
• Acid-Base reactions of Period 3 oxides pt 1

  Acid + Base → Salt + Water

  Alkalis/Bases:

  Na:  2HCl + Na2O → 2NaCl + H2O OR H2SO4 + Na2O → Na2SO4 + H2O

  Mg: 2HCl + MgO → MgCl2 + H2O OR H2SO4 + MgO → MgSO4 + H2O

  Al2O3 can act as an acid AND a base -> Al2O3 is amphoretic

  - acid = H+ donor & base = proton acceptor

  Al (base): 6HCl + Al2O3 → 2AlCl3 + 3H2O OR 3H2SO4 + Al2O3 → Al2(SO4)3 + 3H2O

  Al (acid): Al2O3 + 2NaOH + 3H2O → 2NaAl(OH)4
• Acid-Base reactions of Period 3 oxides pt 2

  Acids:

  Si: SiO2 + 2NaOH → NaSiO3 + H2O

  P: P4O10 + 12NaOH → 4Na3PO4 + 6H2O

  SO2: SO2 + 2NaOH → Na2SO3 + H2O

  SO3: SO3 + 2NaOH → Na2SO4 + H2O

  
  

  Period 3 oxides can react with each other

  6Na2O + P4O10 -> 4Na3PO4

  6MgO + P4O10 -> 2Mg3(PO4)2