1. A Tutorial on Composing Chemical Formulas
By: Liz Essig and Bev Daub
Created in Spring 2003

2. Charges on Elements Back Each element has a charge on it
The charge means how many electrons an element is willing to give up or wanting to take when combined with another element
Example: Ca+2 Li +1
The next slide will show the periodic chart with the charges on the columns of elements

3. Periodic Table of Elements+1 +2
Charges
Back

4. Crossing Charges
Back
Given two elements to make into a compound you must cross the charges, making the element with the positive charge first
This means when you have Sodium and Chlorine, which looks like this Na+1 and Cl-1 respectively, you will end up with Na1 Cl1
The product will be simplified to NaCl, because charges of one do not show up in the resultant composition

5. …Crossing Charges Back
When the charges crossed are both divisible by the same number, just like reducing fractions, you can reduce the charges
For example, given Calcium and Oxygen, Ca+2 and O-2, we cross the charges and get Ca-2O+2
The resultant compound will be CaO because both charges will be reduced

6. …Crossing Charges Back
Now, given Potassium and Nitrogen, we have K+1 and N-3
We cross the charges and we get K-3 N+1
The compound looks like K3N (Potassium Nitride)

7. Crossing the Charges of Polyatomic Ions
Back
Given Magnesium Phosphate, where Phosphate is a polyatomic ion with a –3 charge and looks like PO4
Mg+2 and (PO4)-3 cross charges and it looks like: Mg3(PO4)2
Note: When using a polyatomic ion, parenthesis MUST be placed around the whole polyatomic compound when there is more than a charge of one after it

8. Polyatomic Ion Sheet
Charges: 1 2 3
Back

9. Oxygen Rules
Back
The suffix –ate at the end of a polyatomic ion means there is no loss or gain of oxygen Example: NO3 (Nitrate)
The suffix –ite at the end of a polyatomic ion means there is a loss of one oxygen Example: NO2 (Nitrite)
The prefix hypo- and the suffix –ite, used together, means the loss of two oxygen Example: NO (Hyponitrite)
The prefix Per- and the suffix –ate, used together, means that an oxygen is added Example: NO4 (Pernitrate)

10. Using the Oxygen Rules Back
Given Ammonium and Perphosphate, you have (NH4)+1 and (PO5)-3, the PO4 becomes PO5 because of the Per- and –ate in phosphate
Cross the charges and you will get: (NH4)-3 (PO5)+1
The resulting compound is (NH4)3PO5

11. Acid Rules
Back
Hydrogen is in EVERY acid and is the first component in EVERY acid
The suffix –ic means that there is no oxygen loss or gain Example: H2SO4 (Sulfuric Acid)
The suffix –ous means a loss of one oxygen Example: H2SO3 (Sulfurous Acid)
The prefix Hypo- and the suffix –ous, used together, means a loss of two oxygen
Example: H2SO2 (Hyposulfurous Acid)

12. …Acid Rules
Back
The prefix Per- and the suffix –ic, used together, means a gain of one oxygen Example: H2SO5 (Persulfuric Acid)
The prefix Hydro- and the suffix –ic, used together, means no oxygen and the name and the charge comes right from the periodic chart Example: H2S (Hydrosulfuric Acid)

13. Back
Forming Acids
Given Nitric Acid, you will have Nitrate (NO3 ) -1 and Hydrogen (H+1)
Cross the charges to result in H-1(NO3)+1
The resultant formula is simply HNO3

14. Quiz Back Write the chemical formula for Barium Sulfide.
Write the chemical formula for Lithium Nitride.
Write the chemical formula for Copper II Phosphate.
Answer
Answer
Answer
Periodic Table
Polyatomic Ion Sheet
More Questions

15. Review Crossing Charges and Try Again
Complete Solution
Answer : BaS
Wrong Answer?
Next Question
Review Crossing Charges and Try Again

16. Review Crossing Charges and Try Again
Complete Solution
Ba+2 + S-2  Ba-2 S+2  BaS
Answer : BaS
Wrong Answer?
Next Question
Review Crossing Charges and Try Again

17. Review Crossing Charges and Try Again
Complete Solution
Answer: Li3N
Wrong Answer?
Next Question
Review Crossing Charges and Try Again

18. Review Crossing Charges and Try Again
Complete Solution
Li+1+ N-3 Li-3 N+1 Li3N
Answer: Li3N
Wrong Answer?
Next Question
Review Crossing Charges and Try Again

19. Review the oxygen rules and try again
Complete Solution
Answer: Cu3(PO4)2
Wrong Answer?
Next Question
Review the oxygen rules and try again

20. Review the oxygen rules and try again
Complete Solution
Cu+2+ (PO4)-3 Cu-3 (PO4)+2 Cu3(PO4)2
Answer: Cu3(PO4)2
Wrong Answer?
Next Question
Review the oxygen rules and try again

21. Quiz Back 4) Write the chemical formula for Aluminum Pernitrate.
5) Write the chemical formula for Hydrochloric Acid.
6) Write the chemical formula for Nitrous Acid.
Answer
Answer
Answer
Polyatomic Ion Sheet
End Tutorial

22. Review the oxygen rules and try again
Complete Solution
Answer: Al(NO4)3
Wrong Answer?
Next Question
Review the oxygen rules and try again

23. Review the oxygen rules and try again
Complete Solution
Al+3+ (NO4)-1 Al-1 (NO4)+3 Al(NO4)3
Answer: Al(NO4)3
Wrong Answer?
Next Question
Review the oxygen rules and try again

24. Review the acid rules and try again
Complete Solution
Answer: HCl
Wrong Answer?
Next Question
Review the acid rules and try again

25. Review the acid rules and try again
Complete Solution
H+1+ Cl-1 H-1 Cl+1 HCl
Answer: HCl
Wrong Answer?
Next Question
Review the acid rules and try again

26. Review the acid rules and try again
Complete Solution
Answer: HNO2
Wrong Answer?
End Tutorial
Review the acid rules and try again

27. Review the acid rules and try again
Complete Solution
H+1+ (NO2)-1 H-1 (NO2)+1 HNO2
Answer: HNO2
Wrong Answer?
End Tutorial
Review the acid rules and try again

28. …Crossing Charges
When the charges crossed are both divisible by the same number, just like reducing fractions, you can reduce the charges
For example, given Calcium and Oxygen, Ca+2 and O-2, we cross the charges and get Ca-2O+2
The resultant compound will be CaO because both charges will be reduced
Back to Quiz

29. …Crossing Charges
Now, given Potassium and Nitrogen, we have K+1 and N-3
We cross the charges and we get K-3 N+1
The compound looks like K3N (Potassium Nitride)
Back to Quiz

30. Oxygen Rules
Back to Quiz
Questions 1-3
The suffix –ate at the end of a polyatomic ion means there is no loss or gain of oxygen Example: NO3 (Nitrate)
The suffix –ite at the end of a polyatomic ion means there is a loss of one oxygen Example: NO2 (Nitrite)
The prefix hypo- and the suffix –ite, used together, means the loss of two oxygen Example: NO (Hyponitrite)
The prefix Per- and the suffix –ate, used together, means that an oxygen is added Example: NO4 (Pernitrate)
Back to Quiz
Questions 4-6

31. Acid Rules
Back to Quiz
Hydrogen is in EVERY acid and is the first component in EVERY acid
The suffix –ic means that there is no oxygen loss or gain Example: H2SO4 (Sulfuric Acid)
The suffix –ous means a loss of one oxygen Example: H2SO3 (Sulfurous Acid)
The prefix Hypo- and the suffix –ous, used together, means a loss of two oxygen
Example: H2SO2 (Hyposulfurous Acid)
Part II of Acid Rules

32. …Acid Rules
The prefix Per- and the suffix –ic, used together, means a gain of one oxygen Example: H2SO5 (Persulfuric Acid)
The prefix Hydro- and the suffix –ic, used together, means no oxygen and the name and the charge comes right from the periodic chart Example: H2S (Hydrosulfuric Acid)
Back to Quiz

33. Periodic Table of Elements+1 +2
Back to Quiz

34. 1 2 3 Polyatomic Ion Sheet Charges: Back to Quiz Back to Quiz
Questions 1-3 2
Back to Quiz
Questions 4-6 3

35. Back
Credits
Mr. Wolfe’s Chemistry Notebook