Writing Formulas and Naming Compounds Chapter 18: Section 3

Writing Formulas and Naming Compounds Chapter 18: Section 3

I. Writing Formulas A. Most ionic compounds are formed by combining a metal with a nonmetal B. There are rules for writing formulas for ionic compounds and covalent compounds

II. Writing Formulas for Ionic Compounds A. Ionic compounds that contain two elements are called binary ionic compounds B. Before you can write the formula, you must, be able to determine the oxidation number of each element involved in the compound ? The oxidation number is the number of electrons that an element gains or losses when it reacts with other elements ? Oxidation number is based on the elements family ? The goal is to get the overall charge of the compound to zero

III. How to Write Formulas

A. Write the symbol for each element that has that positive oxidation number (Metal)

B. Write the symbol for each element that has that negative oxidation number (Nonmetal)

C. Use subscripts next to each ion so that the sum of the charges of all the ions is equal to zero

? Examples:

o Magnesium Oxide

+2

-1

Formula: 2

o Step 1: +1 -1

Step 2:

+1

-1

Step 3: 2

1

Step 4: 2

IV. Naming Ionic Compounds A. Write the name of the positive ion B. Write the name of the negative ion using the root term C. Add the ending ?ide to the root in the nonmetal position

? Example: o 3= Aluminum Fluoride o = Sodium Chloride o = Magnesium Bromide o 3= Potassium Nitride o = Calcium Oxide

V. Compounds With Complex Ions A. Some compounds are not binary, they include more than two elements B. An example is baking soda. The formula for baking soda is . This compound contains many ions C. Compounds that contain many ions that are positively or negatively charged are called Polyatomic Ions

VI. Writing Formulas With Polyatomic Ions A. To write formulas for these compounds, do the same as you would with binary compounds B. The one exception is the you must put parenthesis around the polyatomic ion before adding the subscript ? Example: o Barium Chlorate= (3)2

VII. Compounds With Water Added A. A hydrate is a compound with water chemically attached to its ions. The electrons are shared between these atoms B. To name binary covalent compounds, you must use prefixes ? Examples: o 25= Dinitrogen Pentoxide o Tetracarbon Monoxide= 4 o Dihrdrogen Monoxide= 2

VIII. Prefixes for Covalent Compounds A. mono- 1 B. di- 2 C. tri- 3 D. tetra- 4 E. penta- 5 F. hexa- 6 G. hepta- 7 H. octa- 8 I. nona- 9 J. deca- 10

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