A Tutorial on Composing Chemical Formulas By: Liz Essig and Bev Daub Created 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 Charges

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 -2 O +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 K 3 N (Potassium Nitride)

Crossing the Charges of Polyatomic Ions ¤Given Magnesium Phosphate, where Phosphate is a polyatomic ion with a –3 charge and looks like PO 4 ¤Mg +2 and (PO 4 ) -3 cross charges and it looks like: Mg 3 (PO 4 ) 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: 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: NO 3 (Nitrate) ¤The suffix –ite at the end of a polyatomic ion means there is a loss of one oxygen Example: NO 2 (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: NO 4 (Pernitrate)

Using the Oxygen Rules ¤Given Ammonium and Perphosphate, you have (NH 4 )+ 1 and (PO 5 ) -3, the PO 4 becomes PO 5 because of the Per- and –ate in phosphate ¤Cross the charges and you will get: (NH 4 ) -3 (PO 5 ) +1 ¤The resulting compound is (NH 4 ) 3 PO 5

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: H 2 SO 4 (Sulfuric Acid) ¤The suffix –ous means a loss of one oxygen Example: H 2 SO 3 (Sulfurous Acid) ¤The prefix Hypo- and the suffix –ous, used together, means a loss of two oxygen Example: H 2 SO 2 (Hyposulfurous Acid)

…Acid Rules ¤ The prefix Per- and the suffix –ic, used together, means a gain of one oxygen Example: H 2 SO 5 (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: H 2 S (Hydrosulfuric Acid)

Forming Acids ¤Given Nitric Acid, you will have Nitrate (NO 3 ) -1 and Hydrogen (H +1 ) ¤Cross the charges to result in H -1 (NO 3 ) +1 ¤The resultant formula is simply HNO 3

Quiz 1)Write the chemical formula for Barium Sulfide. 2)Write the chemical formula for Lithium Nitride. 3)Write the chemical formula for Copper II Phosphate. Periodic Table Polyatomic Ion Sheet More Questions 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: Li 3 N Review Crossing Charges and Try Again

Review Crossing Charges and Try Again Li +1 + N -3  Li -3 N +1  Li 3 N Answer: Li 3 N

Answer: Cu 3 (PO 4 ) 2 Review the oxygen rules and try again

Answer: Cu 3 (PO 4 ) 2 Cu +2 + (PO 4 ) -3  Cu -3 (PO 4 ) +2  Cu 3 (PO 4 ) 2 Review the oxygen rules and try again

Quiz 4) 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 End Tutorial

Answer: Al(NO 4 ) 3 Review the oxygen rules and try again

Answer: Al(NO 4 ) 3 Al +3 + (NO 4 ) -1  Al -1 (NO 4 ) +3  Al(NO 4 ) 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

Answer: HNO 2

H +1 + (NO 2 ) -1  H -1 (NO 2 ) +1  HNO 2 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 -2 O +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 K 3 N (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: NO 3 (Nitrate) ¤The suffix –ite at the end of a polyatomic ion means there is a loss of one oxygen Example: NO 2 (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: NO 4 (Pernitrate) Questions 1-3 Questions 4-6 Back to Quiz

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: H 2 SO 4 (Sulfuric Acid) ¤The suffix –ous means a loss of one oxygen Example: H 2 SO 3 (Sulfurous Acid) ¤The prefix Hypo- and the suffix –ous, used together, means a loss of two oxygen Example: H 2 SO 2 (Hyposulfurous Acid) Part II of Acid Rules Back to Quiz

…Acid Rules ¤ The prefix Per- and the suffix –ic, used together, means a gain of one oxygen Example: H 2 SO 5 (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: H 2 S (Hydrosulfuric Acid) Back to Quiz

Periodic Table of Elements Back to Quiz

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

Credits Mr. Wolfe’s Chemistry Notebook