Chemical Formulas Ex) NH3 Formulas express the types and numbers of atoms in a compound Symbols are used to represent the types of elements Subscripts are used to represent the number of atoms of each element Ex) NH3

Ionic Compounds Ionic Compound – a compound composed of cations and anions Reminders: Cation – positively charged ion Anion – negatively charged ion Overall charge of the compound is ZERO!

Ionic Compounds Binary ionic compound – an ionic compound composed of two ions metal ion + non–metal ion Metals form monatomic cations Nonmetals form monatomic anions

Writing Ionic Formulas Determine the charges of the ions in the formula. Write ions with charges. Cations MUST be written first. Cross and drop charges. Use the absolute value of each ion’s charge as the subscript for the other ion. NO positive or negative sign. Reduce subscripts to the lowest whole number ratio.

Writing Ionic Formulas Ex) Write the formula for Magnesium Chloride Step 1: Find the charges Step 2: Mg2+ Cl–1 Step 3: MgCl2

Li1+ Cl-1 Ca2+ Br-1 Be2+ S-2 Al3+ O-2 More Examples Lithium chloride Calcium bromide Ca2+ Br-1 Beryllium sulfide Be2+ S-2 Aluminum oxide Al3+ O-2 LiCl CaBr2 Be S = BeS 2 2 Al2O3

Naming Cations & Anions Cation naming pattern metal’s name Ex) K+1 = potassium Anion naming pattern nonmetal’s stem + -ide Ex) F–1 =fluoride

Naming Binary Ionic Compounds Binary ionic compound naming pattern metal’s name + nonmetal’s stem + -ide Ex) KF = potassium fluor ide

More Examples NaCl Sodium chloride Li2O Mg3N2 Lithium oxide Magnesium nitride