Periodicity

• Ionisation energy across a group

  Trend - increases

  explaination:

  • increase number of protons (nuclear charge)
  • outer e in the same main E level/ similar sheilding
  • atomic radius decrease therefore stronger attraction between nucleus and outer e
• Exceptions

  Boron and aluminium

  • e removed from p orbital higher E so further from nucleus so more shielding
• Exceptions

  Oxygen and sulfur

  • paired e in p orbital so repel
• Ionization energy down a group


  Trend - decreases

  explaination:

  • atomic radius increases
  • outer e further away from nucleus therefore increase shielding
  • weaker attraction between nucleus and outer e
• Atomic radius across a group

  Trend - decreases

  explaintion:

  • increase number of protons ( nuclear charge )
  • same main E level ( similar shielding )
  • stronger attraction between nucleus and outer most e
• atomic radius down a group

  Trend- increases

  explaination:

  • e in higher E level
  • increased shielding so attraction between nucleus and outer e
• Electronegativity 


  Electronegativity- the ability of an atom to attract a bonding pair of electron in a covalent bond

  trend across group: increase

  increasing nuclear charge (more protons)

  outer e are in same energy level - similar shielding

  so greater attraction between nucleus and bonding pair of electrons

  trend down a group: decrease

  outer e in higher energy level increased shielding

  bonding electrons further from nucleus

  feels less attraction
• Melting points of period 3 elements 


  Sodium to aluminium - giant metallic lattice - strong electrostatic force of attraction between cations and delocalised electrons

  trend - increases

  increasing number of delocalised e

  cations become more positively charged

  cation decreases in size

  stronger attraction between positive ions and delocalised electrons

  silicon- giant covalent bond- many strong covalent bonds must be broken

  phosphorus to argo - simple covalent molecules - weak van der waals forces between molecules

  strength of van der waals forces depends on number of electrons
• Reactions of period 3 elements in water

  Sodium- stored in oil to prevent reaction with h2o and o2 in air

  2Na +2H2O —— 2NaOH + H2

  observation: effervescence,Na dissolves

  ph:13 (NaOH) —— Na+ + OH+

  fully dissociates

  high concentration of OH-
• Reactions of period 3 elements of water

  magnesium-reacts with o2 in air —- tarnishes (mgo)

  with water- slow

  mg(g) +2h2o (l) —— mg(OH)2 +2OH-

  observation: effervescence,white precipitation

  ph 9-10

  (Mg(OH)2)= Mg2+ +2OH-

  partially dissociates

  low concentration of OH-

  with steam- Mg (g) + H2O —- MgO(s) +H2 (g)

  observation : bright white light white solid
• Reactions of period 3 elements of water

  Aluminium - no reaction due to the coating of Al2O3 on surface

  silicon- no reaction water molecules can not break the strong covalent bonds

  phosphorus- no reaction P4 stored underwater to prevent it reacting with O2 in the air

  sulfur - no reaction
• Reaction of period 3 elements with oxygen 


  Sodium- 4Na+O2 —- 2Na2O

  observation: orange flame,white solid

  magnesium - 2Mg + O2 —- 2MgO

  observation: bright white flame , white solid

  aluminium- 4Al+O2—- 2Al2O3

  observation: white flame , white solid

  silicon- Si + O2 —- SiO2

  observation: white flame , white solid

  phosphorus- P4 + 5O2 —— P4O10

  observation: white flame, white solid

  sulfur- S + O2 —— SO2

  observation: blue flame chocking gas

  SO2 + 1/2 O2 —- SO3
• Reaction of period 3 oxides with water 


  Sodium - Na2O (s) + H2O (l) —- 2NaOH (aq)

  ph - 13 , highly soluble , fully dissociates

  O2- + H2O — 2OH-

  magnesium- MgO (s) + H2O (l) = Mg(OH)2 (s)

  ph- 9-10 , sparingly soluble, only partially dissociates

  aluminium- no reaction

  H2O can not break strong ionic bonds

  silicon- no reaction

  H2O can not break strong covalent bonds
• Reaction of period 3 oxides with water

  phosphorus- no reaction

  P4O10 + 6H2O —— 4H3PO4

  ph - 0-1 ,highly soluble , fully dissociates

  sulfur- SO2 +H2O —- H2SO3 , sulfuric acid , ph 3-4 , slightly soluble so particularly dissolves

  SO3 + H2O —- H2SO4 sulfuric acid

  highly soluble , fully dissociates