Cross Over Rule

In writing compounds the following steps might be used to help you until you become an expert in nomenclature.

Example: Magnesium and chlorine

Step 1:

Write the symbol for the elements, the positive valenced element first, the negative one second.

MgCl

Step 2:

Indicate the valence for each element.

Mg⁺²Cl^-1

Step 3:

Use the cross chain rule.

Mg₁⁺²Cl₂^-1

The subscripts are written without the + or - signs.

If the subscript is 1, it is omitted.

If there is a common factor in the subscripts, it may be reduced.

Step 4:

Write the compound

MgCl₂

Now you try a few!

1. iodine and magnesium

2. sulphur and sodium

3. aluminum and fluorine

4. aluminum and oxygen

5. hydrogen and bromine

6. nitrogen and zinc

7. chlorine and sodium

8. sulphur and barium

9. potassium and nitrogen

10. silver and phosphorus

11. hydrogen and chlorine

Valency chart

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