1. Here we’ll show you how to write a formula for a binary ionic compound in which the metal ion has only one possible charge.

2. Remember, binary compounds are compounds containing only 2 elements Binary Compounds - Compounds containing only 2 elements

3. A Binary Ionic compound is made up of a metal and a non-metal Binary Compounds - Compounds containing only 2 elements Binary Ionic Compounds - Contain a metal and a non-metal

4. On the periodic table, the elements to the left of the staircase are metals and those to the right are non-metals. Metals Non -Metals

5. Here, we’ll write formulas only for compounds of metals with a single charge. These are shaded in green here. We’ll write formulas for compounds formed by the other metals in a later video. Metals with Only One Common Charge

6. We’re asked to write the formula for the compound strontium fluoride. Write the formula for the compound strontium fluoride.

7. We find strontium on the periodic table. It is a metal and its ion is Sr with a positive 2 charge. Write the formula for the compound strontium fluoride.

8. Remember, names for non-metals in binary compounds end in I-D-E, but the names of the elements themselves don’t. So we find an element that sounds like fluoride but doesn’t end in –ide. Write the formula for the compound strontium fluoride.

9. We see it is fluorine, a non-metal with an ion charge of negative one. Write the formula for the compound strontium fluoride.

10. Because strontium is a metal and fluorine is a non-metal, this is an ionic compound. Write the formula for the compound strontium fluoride.

11. The strontium ion in the compound is Sr 2+ Sr 2+ F–F– +2–1 SrF 2 Formula Write the formula for the compound strontium fluoride.

12. The ion that fluorine forms is called the fluoride ion. It has a negative 1 charge. Sr 2+ F–F– F–F– +2–1 SrF 2 Formula Write the formula for the compound strontium fluoride.

13. If we have one Sr2+ ion and one F minus ion, the total positive charge is +2 and the total negative charge is negative 1. Sr 2+ F–F– +2–1 SrF 2 Formula Total Positive Charge Total Negative Charge Write the formula for the compound strontium fluoride.

14. In order for the formula to be correct, the total positive charge and the total negative charge must balance, or add up to zero. Sr 2+ F–F– +2–1 SrF 2 Formula Total Positive Charge Total Negative Charge These must balance and add up to zero Write the formula for the compound strontium fluoride.

15. And these do not add up to zero. Sr 2+ F–F– +2–1 SrF 2 Formula Total Positive Charge Total Negative Charge These DO NOT add up to zero Write the formula for the compound strontium fluoride.

16. So what we do here is add another F minus ion. Sr 2+ F–F– +2–1 SrF 2 Formula Total Positive Charge Total Negative Charge F–F– Add another F – Write the formula for the compound strontium fluoride.

17. The total negative charge is now negative 1 plus negative 1, which is negative 2. Sr 2+ F–F– +2–2 SrF 2 Formula Total Positive Charge Total Negative Charge F–F– Write the formula for the compound strontium fluoride.

18. The positive and negative charges now add up to zero, so they are balanced. Sr 2+ F–F– +2–2 SrF 2 Formula Total Positive Charge Total Negative Charge F–F– NOW these add up to zero Write the formula for the compound strontium fluoride.

19. Because we have one strontium ion and two fluoride ions (click), the formula is SrF2. Write the formula for the compound strontium fluoride. Sr 2+ F–F– +2–2 SrF 2 F–F–

20. We have now answered the question. The final formula for strontium fluoride is SrF2. Notice that no charges are written in the final formula for a compound. If you have any charges in your final formulas, make sure you erase them. Write the formula for the compound strontium fluoride. Sr 2+ F–F– +2–2 SrF 2 Formula: F–F–