oxides

• oxides of elements may be classified as basic acidic or amphoteric
• metallic oxides are basic and non-metallic oxides are acidic
• most metal oxides are basic
• a basic oxide is one that will react with an acid to form a salt and water
• some basic oxides are soluble in water and will react to produce an alkaline solution
• group 1 oxides react in the same way with water
• amphoteric

  oxides react with acids and bases
• oxidation states are useful because they allow us to track of electrons in a type of chemical reaction (redox reaction)
• ch4 is a covalent compound - but we assign oxidation states of -4 for c and +1 for h
• oxidation states

  • if the compound is ionic the oxidation states are the charges on the ions
  • o is -2 and h is +1 - exceptions
  • assign the most electronegative atom in a molecule/ion a negative oxidation state according to how many electrons it needs to gain a noble gas electron configuration
  • the sum of the oxidation states taking into account signs and number of eaxh atom is equal to the overall charge
  • the oxidation state of atoms in element is zero
  • the maximum possible oxidation state is determined by the number of electrons in the outer shell
• a difference in electronegativity values between

  atoms of 1.8 or greater gives rise to ionic character.
• Metal oxides are basic (due to ionic character)
• Non-metal oxides are acidic (due to covalent

  character)
• Compounds that are ionic with some covalent

  character or vice versa can be classed as

  amphoteric.
• Amphoteric oxides show acidic and basic

  properties.
• As electronegativity values increase from

  left to right across a period, ionic character

  will decrease across a period from left to

  right.
• Oxides become more ionic down a

  group as electronegativity decreases

  down a group.
• Ligand Substitution:

  A ligand exchange reaction/substitution reaction

  is a reaction in which one ligand in a complex

  ion is replaced by a stronger ligand from the

  spectrochemical series.
• To determine the overall charge of a complex you will need to know the oxidation state of the transition metal and the charge(s) of the ligand(s).
• We see the complimentary colour to the colour that is

  absorbed.
• Transition metal compounds or complexes are coloured.
• Why are Sc3+ and Zn2+ compounds colourless?


  sc - empty d sub level

  zn - full d sub level
• Splitting of the 3d orbitals

  • The electric field produced by a repulsion between ligand’s lone pair of electrons and transition metal electrons, splits the d sub-level into two sub-levels
  • The energy difference between the levels affects how much energy is absorbed when an electron is promoted.
  • The amount of energy governs the colour of light absorbed.
• In an octahedral complex, two (z2 and x2-y2) go higher and

  three go lower
• In a tetrahedral complex, three (xy, xz and yz) go higher

  and two go lower
• The energy difference between the levels affects how

  much energy is absorbed when an electron is promoted.

  The amount of energy governs the colour of light

  absorbed.
• Transition metals are coloured because:

  • The electric field produced by a ligand’s lone pair of electrons, splits the d sub-level into two sub-level
  • As a photon of light is absorbed a 3d electron from the
  • lower sub-level is excited to the higher sub-level
  • The complimentary colour of the light absorbed is then transmitted
• What factors might affect the energy

  separation between d-orbitals and hence

  the colour of the complex?

  • Identity of the central metal ion:
  • Charge density of the ligand:
  • Geometry of the complex:
  • Oxidation state of the central metal ion:
• Spectrochemical series:

  Arranges ligands according to the energy separation, ∆E, between two sets of d-orbitals.
• Identity of the central metal ion:


  The higher the nuclear charge of a central metal ion, the stronger the coordinate bond between itself and the ligand. As a result there is greater repulsion between 3d

  electrons and the ligands electrons and therefore, greater splitting.
• Charge density of the ligand:


  A ligand with a greater charge density will produce a larger split in the d-orbitals
• Geometry of the complex:


  The splitting in energy of the d orbitals depends on the relative orientation of the ligand and the d orbitals
• Oxidation state of the central metal ion:


  The number of d electrons (i.e. the oxidation state of the metal) will influence the strength of the coordinate bond and the amount of electron repulsion between the d

  electrons and the ligand. The more repulsion, the greater the splitting.
• oxidation state 


  the degree of oxidation of an atom in terms of counting electrons
• for trnsition metal the maximum possible oxidation state is given by the sum of the number of electrons in the s and d subshells
• hydrogen is less electronegative than virtually all the other non-metals