A Tutorial on Composing Chemical Formulas

By: Liz Essig and Bev DaubCreated in Spring 2003

Charges on Elements

¤ 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 He -1

¤ The next slide will show the periodic chart with the charges on the columns of elements

Periodic Table of Elements+1

+2 -3 -2 -1Charges

Crossing Charges¤ 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 Na-1 Cl+1

¤ The product will be simplified to NaCl, because charges of one do not show up in the resultant composition

…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

…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)

Crossing the Charges of Polyatomic Ions

¤ 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

Charges: 1

2

3

Polyatomic Ion Sheet

Oxygen Rules¤ 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)

Using the Oxygen Rules

¤ 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

Acid Rules¤ 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)

…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)

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

Quiz1) Write the chemical formula for Barium Sulfide.

3) Write the chemical formula for Lithium Nitride.

4) Write the chemical formula for Copper II Phosphate.

Periodic Table

Polyatomic Ion SheetMore Questions

Answer

Answer

Answer

Answer : BaS

Review Crossing Charges and Try Again

Answer : BaS

Review Crossing Charges and Try Again

Ba+2 + S-2 Ba-2 S+2 BaS

Answer: Li3N

Review Crossing Charges and Try Again

Review Crossing Charges and Try Again

Li+1+ N-3 Li-3 N+1 Li3N

Answer: Li3N

Answer: Cu3(PO4)2

Review the oxygen rules and try again

Answer: Cu3(PO4)2

Cu+2+ (PO4)-3 Cu-3 (PO4)+2 Cu3(PO4)2

Review the oxygen rules and try again

Quiz4) Write the chemical formula for Aluminum

Pernitrate.

5) Write the chemical formula for Hydrochloric Acid.

6) Write the chemical formula for Nitrous Acid.

Polyatomic Ion Sheet

Answer

Answer

Answer

End Tutorial

Answer: Al(NO4)3

Review the oxygen rules and try again

Answer: Al(NO4)3

Al+3+ (NO4)-1 Al-1 (NO4)+3 Al(NO4)3

Review the oxygen rules and try again

Answer: HCl

Review the acid rules and try again

Answer: HCl

H+1+ Cl-1 H-1 Cl+1 HCl

Review the acid rules and try again

Review the acid rules and try again

Answer: HNO2

Answer: HNO2

H+1+ (NO2)-1 H-1 (NO2)+1 HNO2

Review the acid rules and try again

…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

…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

Oxygen Rules¤ 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)

Questions 1-3

Questions 4-6

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Acid Rules¤ 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

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…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

Periodic Table of Elements+1

+2 -3 -2 -1

Back to Quiz

Charges:1

2

3

Polyatomic Ion Sheet

Questions 1-3

Questions 4-6

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Back to Quiz

Credits

Mr. Wolfe’s Chemistry Notebook