Section 3: Compound Names and Formulas Preview Key Ideas Bellringer Naming Ionic Compounds Naming Covalent Compounds Empirical Formulas

Key Ideas How are ionic compounds named? What do the numerical prefixes used in naming covalent compounds tell you? What does a compound’s empirical formula indicate?

Bellringer A compound word is two words joined together to form a new word. Use the list of words on the following slide to form 20 compound words.

Bellringer, continued berg snow side thumb pitch tack yard ice quake bug pot frog flag cloth dream brow lady burns day stack leap port arm fork chair earth drift stick eye pole table oat left meal overs hay belly car box air

Naming Ionic Compounds How are ionic compounds named? The names of ionic compounds consist of the names of the ions that make up the compounds. Names of cations include the elements of which they are composed. Example: a sodium atom loses an electron to form a sodium ion, Na+. Names of anions are altered names of elements. Example: a fluorine atom gains an electron to form a fluoride ion, F–.

Naming Ionic Compounds, continued An ionic compound must have a total charge of zero. If an ionic compound is made up of ions that have different charges, the ratio of ions will not be 1:1. CaF2 Some cation names must show their charge. Transition metals may form several cations—each with a different charge. Fe2O3 is made of Fe3+ ions, so it is named iron(III)oxide. FeO is made of Fe2+ ions, so it is named iron(II) oxide.

Naming Ionic Compounds, continued To determine the charge of a transition metal cation, look at the total charge of the compound. Fe2O3 The total charge of the compound is zero. The iron ion has a charge of 3+. An oxide ion, O2–, has a a charge of 2–. Fe2O3 : (2 × 3+) + (3 × 2–) = 0

Visual Concept: Reading Chemical Formulas

Visual Concept: Naming Ionic Compounds

Math Skills Writing Ionic Formulas What is the chemical formula for aluminum fluoride? 1. List the symbols for each ion. Symbol for an aluminum ion: Al3+ Symbol for a fluoride ion: F– 2. Write the symbols for the ions, with the cation first. Al3+ F–

Math Skills, continued 3. Find the least common multiple of the ions’ charges. The least common multiple of 3 and 1 is 3. To make a neutral compound, you need a total of three positive charges and three negative charges. you need only one Al3+ ion: 1 × 3+ = 3+ you need three F– ions: 3 × 1– = 3– 4. Write the chemical formula. Show with subscripts how many of each ion are needed to make a neutral compound. AlF3

Naming Covalent Compounds What do the numerical prefixes used in naming covalent compounds tell you? For covalent compounds of two elements, numerical prefixes tell how many atoms of each element are in the molecule. Numerical prefixes are used to name covalent compounds of two elements.

Naming Covalent Compounds, continued Examples: Boron trifluoride, BF3 contains one boron atom and three fluorine atoms. Dinitrogen tetroxide, N2O4, is made of two nitrogen atoms and four oxygen atoms.

Visual Concept: Naming Covalently-Bonded Compounds

Visual Concept: Naming Compounds Using Numerical Prefixes

What does a compound’s empirical formula indicate? Empirical Formulas What does a compound’s empirical formula indicate? An empirical formula tells us the smallest whole-number ratio of atoms that are in a compound. empirical formula: the composition of a compound in terms of the relative numbers and kinds of atoms in the simplest ratio

Empirical Formulas, continued Different compounds can have the same empirical formula. Molecular formulas are determined from empirical formulas. molecular formula: a chemical formula that shows the number and kinds of atoms in a molecule, but not the arrangement of atoms Masses can be used to determine empirical formulas.

Visual Concept: Comparing Molecular and Empirical Formulas

Math Skills Finding Empirical Formulas One mole of an unknown compound contains 62 g of phosphorus and 80 g of oxygen. What is the empirical formula of this compound? 1. List the given and unknown values. Given: 62 g phosphorus, 80 g oxygen Unknown: empirical formula 2. Write the atomic masses. phosphorus: 30.97 g/mol oxygen: 16.00 g/mol

Math Skills, continued 3. The molar ratio of elements in the compound will be the compound’s empirical formula. Empirical Formula: P2O5