The following notes were written for the previous IB syllabus (2009). The new IB syllabus for first examinations 2016 can be accessed by clicking the link below.

IB syllabus for first examinations 2016

Periodicity (hl)

13.1 - Trends across period 3

Characteristic Trend (left to right) Reason
Atomic radius decreases in size from left to right increased attractive force (acting on the same energy shell) from the nucleus as the number of protons (and hence the nuclear charge) increases
Ionic radius decreases across the period until formation of the negative ions then there is a sudden increase followed by a steady decrease to the end In general as above. The sudden increase on formation of negative ions is due to the new (larger) outer shell
Electronegativity Increases More electron attracting power of the larger nuclear charge as we move to the right
Metallic character Decreases - Na, Mg, Al metals; Si metalloid; P, S, Cl, Ar non-metals Metallic character is a measure of the ease of loss of electrons from the outer shell. This decreases with increasing nuclear charge.
Oxides Na, Mg - alkaline
Al - amphoteric
Si, P, S, Cl -acidic
Chloride character NaCl - ionic
MgCl2 - some covalent character
AlCl3 - covalent
The remainder covalent
Increasing charge density of the positive ion polarises the chloride ion as we move to the right hand side
Melting point NaAl steady increase Increasing availability of electrons in the metallic bonding associated with greater charge density of the metal ion
Si massive increase Si giant macromolecular structure
P large decrease P4 molecules
S small increase S8 molecules
Cl Ar decrease Cl2 molecules and Ar atoms

Chemical periodicity of period 3 oxides

  Na2O MgO Al2O3 SiO2


(or P4O6)


(or SO2)



Add H2O Na2O + H2O -> 2NaOH MgO + H2O -> Mg(OH)2 Insoluble Insoluble

P4O10 + 6H2O -> 4H3PO4

P4O6+ 6H2O -> 4H3PO3

SO3 + H2O -> H2SO4

SO2 + H2O -> H2SO3

Cl2O7 + H2O -> 2HClO4

Cl2O + H2O -> 2HOCl

Add HCl Na2O + H+ -> 2Na+ + H2O MgO + 2H+ -> Mg2+ + H2O Al2O3 + 6H+ -> 2Al3+ + 3H2O No reaction No reaction No reaction No reaction
Add NaOH No reaction No reaction Al2O3 + 2OH- + 3H2O -> 2Al(OH)4 SiO2 + 2OH- -> SiO32- + H2O

H3PO4 + OH- -> H2PO4- + H2O

H3PO3 + OH- -> H2PO3- + H2O

SO2 + OH- -> HSO4-

SO2 + OH- -> HSO3-

HCl2O7 + OH- -> Cl2O72- + H2O

HOCl + OH- -> OCl- + H2O

Nature Basic Oxide Basic Oxide Amphoteric Oxide Acidic Oxide Acidic Oxide Acidic Oxide Acidic Oxide
Conductivity Good Good Good None None None None
Melting Point 1275 2852 2027 1610 24 17 -92

Chemical periodicity of period 3 chlorides

NaCl MgCl2 Al2Cl6 SiCl4 PCl3 PCl5 Cl2
Add H2O Dissolves to give free ions Dissolves to give free ions Hydrolysis to give [Al(H2O)6]3+ and Cl- ions Reacts to produce HCl and Si(OH)4 Reacts to produce H3PO3 and HCl Reacts to produce H3PO4 and HCl Dissociates to give HOCl and HCl
Nature ionic ionic covalent covalent covalent covalent covalent
Conductivity Good Good None None None None None
Melting Point 801 714 178 -70 -112   -101
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13.2 - First-row d-block elements

Characterised by the following properties:

Variable oxidation state

The multiple oxidation states of the d-block (transition metal) elements are due to the proximity of the 4s and 3d sub shells (in terms of energy). All transition metals exhibit a 2+ oxidation state (both electrons being lost from the 4s and all have other oxidation states (common).

Sc Ti  V Cr Mn Fe Co Ni Cu Zn
+2 +2 +2 +2 +2 +2 +2 +2 +2
+3 +3 +3 +3 +3 +3 +3 +3
+4 +4 +4
+6 +6 +6

Coordinated ligands

Ligands are the molecules (or ions) which donate an electron pair to form a dative covalent bond with the central transition metal atom (forming a complex molecule or ion).



These are species which are formed around a central atom, with other atoms, ions or molecules donating an electron pair to form a covalent bond to this central atom. The result is a "complex" usually an ion but may also be a molecule.

Complex shape ligands coordination number name
[Fe(H2O)6]3+ octahedral water 6 hexa-aqua iron III ion
[Fe(CN)6]3- octahedral cyanide CN- 6 hexacyano ferrate III ion
[CuCl4]3- tetrahedral chloride Cl- 4 tetrachloro cuprate I ion
[Cu(NH3)4]2+ square planar ammonia 4 tetra-ammine copper II ion
[Ag(NH3)2]+ linear ammonia 2 diammine silver I ion
Ni(CO)4 tetrahedral carbon monoxide 4 tetracarbonyl Nickel 0 molecule
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Coloured compounds

The color in the transition metals (d-block) is predominantly due to the splitting of the d shell orbitals into slightly different energy levels. As a result, certain wavelengths of energy can be absorbed by the d-block elements (with electrons jumping between these slightly different energy levels), resulting in the complement color being visible.

Colour is affected by both the oxidation state of the transition metal and the type of ligand

Complex ion Oxidation state of metal colour ligand
[Fe(H2O)6]3+ III pale green water
[Fe(H2O)6]2+ II yellow water
[Cu(H2O)6]2+ II blue water
[Cu(NH3)4]2+ II deep blue ammonia
[CuCl4]2- II green chloride ion

Crystal field theory


Transition metals and their ions often have unpaired 'd' electrons which produce an asymmetric magnetic field that can be detected. This is called paramagnetism


Complex ion electronic configuration no of unpaired electrons magnetism
[Fe(H2O)6]3+ [Ar]4s0 3d5 5 paramagnetic
[Cr(H2O)6]3+ [Ar]4s0 3d3 3 paramagnetic
[Cu(H2O)6]2+ [Ar]4s0 3d9 1 paramagnetic
[Ni(NH3)6]2+ [Ar]4s0 3d8 2 paramagnetic
[CoCl4]2- [Ar]4s0 3d7 3 paramagnetic

Catalytic activity

'd' block elements make good catalysts due to their multiple oxidation states (hence their ability to react with different species and produce a path of lower activation energy, and so allow the reaction to proceed at a faster rate). Another possible reason for their catalytic activity is their available 'd' orbitals which allow reacting molecules to co-ordinate to the surface of the transition metal which in turn weakens the bonding within the molecule allowing it to react.


  • MnO2 in decomposition of hydrogen peroxide
  • V2O5 in the contact process
  • Fe in Haber process
  • Ni in conversion of alkenes to alkanes
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