IB Chemistry SL

Revision Notes

9.1.4 Naming Transition Metal Compounds

Naming Transition Metal Compounds

  • Transition metals are characterized by having variable oxidation numbers.
  • Oxidation numbers can be used in the names of compounds to indicate which oxidation number a particular element in the compound is in
  • Where the element has a variable oxidation number, the number is written afterwards in Roman numerals.
  • This is called the STOCK NOTATION (after the German inorganic chemist Alfred Stock), but is not widely used for non-metals, so SO2 is sulphur dioxide rather than sulphur(IV) oxide
  • For example, iron can be both +2 and +3 so Roman numerals are used to distinguish between them
    • Fe2+ in FeO can be written as iron(II) oxide
    • Fe3+ in Fe2O3 can be written as iron(III) oxide

Worked Example

Can you name these transition metal compounds?

  1. Cu2O
  2. MnSO4
  3. Na2CrO4
  4. KMnO4
  5. Na2Cr2O7

Answer:

Answer 1: copper(I) oxide:

The ox. no. of 1 O atom is -2 and Cu2O has overall no charge so the ox. no. of Cu is +1

Answer 2: manganese(II) sulfate:

The charge on the sulfate ion is -2, so the charge on Mn and ox. no. is +2

Answer 3: sodium chromate(VI):

The ox. no. of 2 Na atoms is +2 so CrO4 has an overall -2 charge, so the ox. no. of Cr is +6

Answer 4: potassium manganate(VII):

The ox. no. of a K atom is +1 so MnO4 has overall -1 charge, so the ox. no. of Mn is +7

Answer 5: sodium dichromate(VI):

The ox. no. of 2 Na atoms is +2 so Cr2O7 has an overall -2 charge, so the ox. no. of Cr is +6. To distinguish it from CrO4 we use the prefix di in front of the anion

Exam Tip

The answer to No. 2 should strictly speaking being managanese(II) sulfate (VI) since  sulfur is an element with a variable oxidation number. However, it is a common ion whose name and formula you should know and you are only required to name transition metal compounds using Stock Notation

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