5. Formulas and Names of Ionic Compounds

Ionic Compounds Mg2+ Cl- _ Al3+ Cl- _ K+ O2- _ _ Balanced Not Balanced Compounds are neutral. This means that the total number of electrons and protons is the same. The ionic charges must also “balance” or add up to 0. Balanced Not Balanced Mg2+ Cl- + + _ Al3+ Cl- + + + _ K+ O2- + _ _

Ionic Compounds Al3+ Mg2+ Cl- _ Cl- _ + + + + + This means we can predict the ratio that metal ions will bond with nonmetal ions. The ratio is reflected in the subscripts in the chemical formula. Al3+ Cl- + + + _ Mg2+ Cl- + + _ Ratio- 1 Mg2+: 2 Cl- Formula- MgCl2 Name- magnesium chloride Ratio- 1 Al3+: 3 Cl- Formula- AlCl3 Name- aluminium chloride

Writing formulas of binary ionic compounds The symbol of each type of atom is in the formula of the compound. The metal ion or cation is written first. The subscript shows number of each atom in the smallest repeating unit or the ratio of the cation:anion. This ratio is the same in every sample of the compound, no matter how large or how small the sample-two atoms or 106 atoms. Reduce the ratio to the least common multiple. Leave out the number one (NaCl not Na1Cl1) and ion charges. Na1Cl1 ➜ NaCl subscripts

Writing IUPAC names of ionic compounds The scientific name of each compound includes the ions that are in it. The metal ion (cation) is written first. The non-metal ion (anion) is written last. The name of non-metal ions end in ide. metal non-metal sodium chloride N

Summary Determine the cation and anion and their charges. Determine the ratio of the cation : anion in a neutral compound Write the formula with subscripts representing ratios. The metal comes first. Write the name of the cation followed by the anion. Non-metals ions end in ide. No upper case letters. Remove 1s and reduce if necessary. CATION + charge metal ion ANION - charge non-metal ion 3 Mg2+ + + + + + + 2 N3- - - - - - - Mg3N2 magnesium nitride Mg2O2 ➜ Mg1O1 ➜ MgO

Practice using manipulatives Use the ion kits to build as many binary ionic compounds as you can. Write the ratio, formula and name in a table. Ratio of cation to anion to be neutral Compound formula Compound name 1Mg2+ : 2Cl- MgCl2 magnesium chloride 1Mg2+ : 1O2- MgO magnesium oxide 2Al3+ : 3O2- Al2O3 aluminum oxide

Patterns in formulas Na2S Na2O K2O K2S Any member of a group can replace any other member of a group in the formula to make a new compound. The ratio in the formula will not change when you substitute other group members. Na2S Na2O K2O K2S

Periodic table patterns in ionic compound formation Period 2 elements Ion/Group N3- O2- F- 15 16 17 Li+ 1 3:1 2:1 1:1 Be2+ 2 3:2 2:2 1:2 B3+ 3 3:3 2:3 1:3