22.3 – Writing formulas and Naming Compounds

Objectives Explain how to determine oxidation numbers Write formulas and names for ionic compounds

Binary Ionic Compounds A compound composed of 2 elements To write a chemical formula for a binary compound, you need to know: which elements are involved how many electrons they lose or gain to become stable

Oxidation Numbers - Transition Elements Because they can have multiple oxidation numbers, we have to express that number in the name with a Roman Numeral For example, the oxidation number of iron in iron (III) oxide is 3+.

Write Formulas for these Potassium ion Magnesium ion Copper (II) ion Chromium (VI) ion Barium ion Mercury (II) ion

Ionic Compounds are NEUTRAL Although the individual ions in a compound carry charges, the compound itself is neutral A formula must have the right number of positive ions and the right number of negative ions so the charges balance

Ca+2 Cl-1 would have a +1 charge. Need another Cl-1 Ca+2 Cl 1- Cl 1- Writing Formulas Write the formula for calcium chloride. Calcium is Ca+2 Chloride is Cl-1 Ca+2 Cl-1 would have a +1 charge. Need another Cl-1 Ca+2 Cl 1- Cl 1- CaCl2

Step By Step – Writing Formulas 1. Write the symbol of the element (or polyatomic ion) with the positive oxidation number or charge 2. Write the symbol of the element (or polyatomic ion) with the negative oxidation number or charge 3. The charge (without the sign) of one ion becomes the subscript of the other ion. Reduce the subscripts to the smallest whole numbers that retain the ratio of ions.

Criss-Cross Method

Write the formulas for these Lithium sulfide Tin (II) oxide Tin (IV) oxide Magnesium fluoride Copper (II) sulfate Iron (III) phosphide Gallium nitrate Iron (III) sulfide Barium nitrate

In-Class Assignment/Homework 22.3a Criss Cross WS 22.3a Criss-Cross practice