5.8 Ionic Compounds

5.8 IONIC COMPOUNDS The process in which an atom gains or loses electrons to become more stable explains how some compounds are formed. An ionic compound is composed of positive and negative ions. Positively charged metals (cation) are attracted to negatively charged nonmetals (anion) to form an ionic compound. The attraction between the atoms of opposite charges is called an ionic bond. Example: Na+ positive metal

+

Cl-

Na+Cl-

negative nonmetal

ionic cmpd.

5.8 Writing Formulas for Ionic Compounds Step 1: Write the chemical symbol for the metal, followed by the chemical symbol for the nonmetal. Step 2: Write the charge of each ion as a superscript after the symbol. Step 3: Use the crisscross method to fill in the number of atoms of each element in the compound. The number is written as a subscript. *Must be in the lowest form, therefore, reduce if possible. Examples: a) Write the formula for beryllium fluoride. Step 1: Step 2: Step 3:

Be F Be+2 F-1 BeF2

b) Write the formula for nickel oxide. Step 1: Step 2: Step 3: Reduce:

Ni O Ni+2 O-2 Ni2O2 NiO

c) Write the formula for copper (II) chloride Step 1: Step 2: Step 3:

Cu Cl Cu+2 Cl-1 CuCl2

5.8 Write the formulas for the following ionic compounds:

numerals 1)Roman aluminum sulfide indicate a multivalent atom.

2) tin (IV) oxide

3) calcium fluoride

4) potassium bromide

5) iron (III) phosphide

5.8 Naming Ionic Compounds The name of the metal is always first, followed by the name of the nonmetal. The ending of the nonmetal is changed to “ide”. Nonmetal examples: fluorine = bromine =

fluoride bromide

chlorine = oxygen =

chloride oxide

The ionic compound formed by sodium and sulfur is sodium sulfide. Naming Multivalent Ionic Compounds Some metals can form more than one kind of ion when combined to the same nonmetal. (CuCl is white while CuCl2 is yellow.) You have to use the Roman numeral system when naming ions of metals that have more than one ionic charge. Refer to handout: Oxidation Numbers when naming these compounds. Some Common Multivalent Metals Element Copper Iron Lead Tin Palladium Cobalt

Symbol Cu Fe Pb Sn Pd Co

Ionic +1 +2 +2 +2 +2 +2

Charges +2 +3 +4 +4 +4 +3

Roman Num. I II II III II IV II IV II IV II III