Ionic Compounds Writing Formulas
Ionic Compounds Metal + Nonmetal Can have a polyatomic ion Cation is first Anion is second TOTAL charge has to be zero!
Transition Metals Can form different ions Ion charge is indicated with romal numerals after the element’s name Example: copper(I) has a +1 charge
Steps for Writing Formulas Several examples will follow this slide! Write out the two parts that will be in the compound. Look up the charge and write it as a superscript for each part. Cross the numbers (no signs). Reduce the formula to the lowest numbers.
Example 1 What is the formula for the ionic compound made from sodium and fluorine?
1. Write out the two parts that will be in the compound. Na F What is the formula for the ionic compound made from sodium and fluorine?
2. Look up the charge and write it as a superscript for each part. - Na + F What is the formula for the ionic compound made from sodium and fluorine?
3. Cross the numbers (no signs). - Na + F 1 1 What is the formula for the ionic compound made from sodium and fluorine?
4. Reduce the numbers. Na F 1 1 What is the formula for the ionic compound made from sodium and fluorine?
5. Rewrite as a finished formula. Na F What is the formula for the ionic compound made from sodium and fluorine?
Wrap-Up 1 What is the formula for a compound made from lithium and bromine? LiBr
Example 2 What is the formula for the ionic compound made from aluminum and iodine?
1. Write out the two parts that will be in the compound. Al I What is the formula for the ionic compound made from aluminum and iodine?
2. Look up the charge and write it as a superscript for each part. - Al 3+ I What is the formula for the ionic compound made from aluminum and iodine?
3. Cross the numbers (no signs). - Al 3+ I 1 3 What is the formula for the ionic compound made from aluminum and iodine?
4. Reduce the numbers. Al I 1 3 What is the formula for the ionic compound made from aluminum and iodine?
5. Rewrite as a finished formula. AlI 3 What is the formula for the ionic compound made from aluminum and iodine?
Wrap-Up 2 What is the formula for a compound made from beryllium and chlorine? BeCl2
Example 3 What is the formula for the ionic compound made from potassium and nitrogen?
1. Write out the two parts that will be in the compound. K N What is the formula for the ionic compound made from potassium and nitrogen?
2. Look up the charge and write it as a superscript for each part. + 3- K N What is the formula for the ionic compound made from potassium and nitrogen?
3. Cross the numbers (no signs). 3- K + N 3 1 What is the formula for the ionic compound made from potassium and nitrogen?
4. Reduce the numbers. K N 3 1 What is the formula for the ionic compound made from potassium and nitrogen?
5. Rewrite as a finished formula. K3N What is the formula for the ionic compound made from potassium and nitrogen?
Wrap-Up 3 What is the formula for a compound made from cesium and sulfur? Cs2S
Example 4 What is the formula for the ionic compound made from magnesium and selenium?
1. Write out the two parts that will be in the compound. Mg Se What is the formula for the ionic compound made from magnesium and selenium?
2. Look up the charge and write it as a superscript for each part. 2- 2+ Mg Se What is the formula for the ionic compound made from magnesium and selenium?
3. Cross the numbers (no signs). 2- Mg 2+ Se 2 2 What is the formula for the ionic compound made from magnesium and selenium?
Mg Se 4. Reduce the numbers. 2 2 What is the formula for the ionic compound made from magnesium and selenium?
5. Rewrite as a finished formula. MgSe What is the formula for the ionic compound made from magnesium and selenium?
Wrap-Up 4 What is the formula for a compound made from indium and arsenic? InAs
Example 5 What is the formula for the ionic compound made from iron(III) and oxygen?
1. Write out the two parts that will be in the compound. Fe O What is the formula for the ionic compound made from iron(III) and oxygen?
2. Look up the charge and write it as a superscript for each part. 2- O Fe 3+ What is the formula for the ionic compound made from iron(III) and oxygen?
3. Cross the numbers (no signs). 2- Fe 3+ O 2 3 What is the formula for the ionic compound made from iron(III) and oxygen?
4. Reduce the numbers. Fe O 2 3 What is the formula for the ionic compound made from iron(III) and oxygen?
5. Rewrite as a finished formula. Fe2O3
Wrap-Up 5 What is the formula for a compound made from lead(IV) and sulfur? PbS2
Example 6 What is the formula for the ionic compound made from sodium and phosphate?
1. Write out the two parts that will be in the compound. Na PO4 What is the formula for the ionic compound made from sodium and phosphate?
2. Look up the charge and write it as a superscript for each part. 3- + Na PO4 What is the formula for the ionic compound made from sodium and phosphate?
3. Cross the numbers (no signs). 3- + Na PO4 3 1 What is the formula for the ionic compound made from sodium and phosphate?
PO4 Na 4. Reduce the numbers. 3 1 What is the formula for the ionic compound made from sodium and phosphate?
5. Rewrite as a finished formula. Na3PO4
Wrap-Up 6 What is the formula for a compound made from cesium and sulfite? Cs2SO3
Example 7 What is the formula for the ionic compound made from chromium(III) and nitrate?
1. Write out the two parts that will be in the compound. Cr NO3 What is the formula for the ionic compound made from chromium(III) and nitrate?
2. Look up the charge and write it as a superscript for each part. 3+ - Cr NO3 What is the formula for the ionic compound made from chromium(III) and nitrate?
3. Cross the numbers (no signs). 3+ - Cr NO3 1 3 What is the formula for the ionic compound made from chromium(III) and nitrate?
Cr (NO3) 4. Reduce the numbers. 1 3 If the number by the polyatomic ion can’t reduce, draw parentheses around the ion’s formula What is the formula for the ionic compound made from chromium(III) and nitrate?
5. Rewrite as a finished formula. Cr(NO3)3 What is the formula for the ionic compound made from chromium(III) and nitrate?
Wrap-Up 7 What is the formula for a compound made from ammonium and sulfur? (NH4)2S