SECTION 3: COMPOUND NAMES

AND 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?

KEY TERMS

Empirical formula

Anion

Molecular formula

Cation

NAMING IONIC COMPOUNDS

The names of ionic compounds consist of the names of the ions that make up the compounds

Name of cations include the elements of which they are composed

Ion name and symbol

Cesium ion, Cs+

Lithium ion, Li+

Sodium ion, Na+

Barium ion, Ba2+

Calcium ion, Ca2+

Aluminum ion, Al3+

Ion charge

1+ 2+ 3+

NAMING IONIC COMPOUNDS

Names of anions are altered names of elements NaF: is made of sodium ions, Na+, and fluoride

ions, F-. Therefore, its name is sodium fluoride 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 will not be 1:1 For calcium fluoride to have a total charge of

zero, there must be two fluoride ions for every calcium ion

NAMING IONIC COMPOUNDS

Some cation names must show their charge The charge of the iron cation in Fe2O3 is

different from the charge of the iron cation in FeO. In cases such as this, the cation name must be followed by a Roman numeral in parentheses that shows the cation’s 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

Determine the charge of a transition metal cation How can you tell that the iron ion in Fe2O3 has a

charge of 3+? Write formulas for ionic compound using

names You can find the charge of each ion in a

compound if you are given the compound’s formula. You can find the formula for a compound if you are given the compound’s name

NAMING IONIC COMPOUNDS

Math Skills: Writing Ionic Formulas Go to go.hrw.com and enter keyword

HK8MP

NAMING COVALENT COMPOUNDS

For covalent compounds or 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 If there is only one atom of the first element,

the name does not get a prefix The element farther to the right in the periodic

table is named second and ends in –ide One boron atom and three fluorine atoms

make up boron trifluoride, BF3

EMPIRICAL FORMULAS

An empirical formula tells us the smallest whole-number ratio of atoms that are in a compound

Different compounds can have same empirical formula

Molecular formulas are determined from empirical formulas

Masses can be used to determine empirical formulas

EMPIRICAL FORMULAS

Empirical formula: the composition of a compound in terms of the relative number and kinds of atoms in the simplest ratio

Molecular formula: a chemical formula that shows the number and kinds of atoms in a molecule, but not the arrengement of atoms

EMPIRICAL FORMULAS

Math Skills: Finding Empirical Formulas Go to go.hrw.com and enter keyword

HK8MP

HOMEWORK