Some
elements have more than one valence they may use when bonding. The Stock system uses Roman numerals to
indicate which valence the element is using in a particular compound.
Rules for Writing a Name
from a Formula
1. Write
down the name of the first element. This
is the element that may have more than one valence.
2. Include
a Roman numeral to represent the valence of the first element (reverse the
‘criss-cross’ to determine the valence).
3. Remove
the ending on the name of the second element and add the “-ide” ending.
ex.(a)
FeCl2 Fe2 Cl1 iron (II) chloride
(b) FeCl3 Fe3 Cl1 iron (III) chloride
(c) SnO Sn1 O1 tin (II) oxide *this is a special case – reversing the criss-cross tells us that the valence of oxide is 1, which is not possible – the valence of oxide must be 2. This formula must have been reduced to a simplest ratio. Therefore, reversing the criss-cross should give us: Sn2 O2, giving us the name tin (II) oxide
1. Write
down symbols for the two elements, in the order they appear in the name.
2. Place
the valence of the first element above the first symbol (Roman numeral).
3. Place
the valence of the second element above the second symbol.
4. Use
the ‘criss-cross’ rule and write the numbers as subscripts.
5. Reduce
the subscript numbers to the simplest ratio.
ex.(a)
copper (II) oxide Cu2 O2 ↝ Cu2O2 ↝ CuO
(b)
chromium (III) sulfide Cr3 S2 ↝
Cr2S3
Need a bit more Stock system in your life? Check out this video.
Give the correct formula for the following. Do as many questions as it takes to get 10 correct.
1. copper
(I) oxide
2. copper
(II) oxide
3. tin
(IV) chloride
4. mercury
(II) bromide
5. iron
(III) fluoride
6. chromium
(III) oxide
7. chromium
(II) oxide
8. iron
(II) chloride
9. sulfur
(VI) fluoride
10. arsenic
(III) iodide
11. lead
(II) oxide
12. cobalt
(II) nitride
13. cobalt
(III) sulfide
14. phosphorus
(III) chloride
15. phosphorus
(V) iodide
16. manganese
(III) oxide
17. nickel
(II) oxide
18. cobalt
(III) fluoride
19. gold
(I) bromide
20. lead
(II) sulfide
21. iron
(III) phosphide
22.
23. mercury
(I) sulfide
24. tin
(II) phosphide
25. nitrogen
(V) sulfide
26. tin
(IV) oxide
27. copper
(I) iodide
28. phosphorus
(III) chloride
29. sulfur
(VI) oxide
30. silicon
(IV) chloride
Give the correct name for the following. Do as many questions as it takes to get 10 correct.
1. SnF2
2. SnF4
3. Cu2S
4. CuS
5. Cr2O3
6. SnS
7. Fe2O3
8. HgCl2
9. CoCl3
10. Co3N2
11. PbO
12. As2S3
13. PCl3
14. P2O5
15. PbCl4
16. Cu2O
17. HgI
18. Fe2S3
19.
20. NCl3
21. As2S5
22. Au2O3
23. NiO
24. SnF4
25. MnO
26. PCl5
27. Cu3N2
28. Cu3N
29. PbS
30. Ni2O3
Answer Keys:
