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?
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