Chapter 7 – Chemical Formulas & Compounds

I. Chemical Names and Formulas

• All natural and synthetic substances have chemical names, however, most substances are better known by common names

Chemical Name Common Name

Calcium carbonate Limestone

Sodium chloride Table salt

Dihydrogen monoxide Water

Sodium bicarbonate Baking soda

Acetic acid Vinegar

Nitrous oxide Laughing gas

• A. Significance of a Chemical Formula• 1. Chemical formula – indicates the number

of atoms of each element in a compound• 2. Molecular formula – the number of

atoms of each element in a single molecule• a. Octane – C8H18

• b. Octane is a hydrocarbon, which means it is a molecular compound made of carbon and hydrogen only

BenzeneMethane Ethane Propane Butane

• 3. Formula unit – the simplest ratio of cations and anions in an ionic compound

• a. Sodium chloride – NaCl• b. Aluminum sulfate – Al2(SO4)3

• c. Potassium hydroxide – KOH• B. Monatomic Ions• 1. Monatomic ions – ions formed from a single

atom• 2. A monatomic cation is named the same name as

the element• 3. A monatomic anion uses the first part of the

element’s name, but drops the last part of the name and adds the suffix -ide

• C. Binary Ionic Compounds• 1. Binary compounds – compounds

composed of only two elements• 2. In a binary compound, the total number of

positive charges must equal the total number of negative charges; therefore, the formula unit is neutral

• 3. The binary compound is named by using its cation name first and its anion name second Sodium chloride

• 4. Use the following steps to write the formula for binary ionic compounds:

• a. Write the symbol for the cation first• b. Write the symbol for the anion second• c. Use superscripts to write the charge of each ion• d. check to see if the charges balance out to zero• e. If the charges balance to zero, then the formula

unit will simply be the two elements’ symbols with no subscripts

• f. If the charges do not balance out to zero, then use the anion’s charge as a subscript for the cation, and the cation’s charge as a subscript for the anion, and this becomes the formula unit

• D. Naming Binary Ionic Compounds• 1. Nomenclature – refers to the naming

system used to name the compound• 2. Stock system – a naming system using

Roman numerals to indicate the charge of the cation

• a. Some metals (transition metals) can form two or more cations

• b. Roman numerals are enclosed in parenthesis and written right after the name of the cation FeCl2 - Iron (II )chloride Fe2O3 - Iron (III) oxide

• E. Compounds Containing Polyatomic Ions• 1. Ionic compounds may contain more than just

two elements, in which case, they contain a metal and a polyatomic ion (NaOH – sodium hydroxide)

• 2. If the polyatomic ions contain oxygen, then it is called an oxyanion (SO4 NH4)

• 3. The oxyanion may contain one or more oxygen atoms (CO3

-2 carbonate or CO2

-2 carbonite)

• a. the oxyanion with the greater number of oxygen atoms has a suffix ending of –ate

• b. the oxyanion with the smaller number of oxygen atoms has a suffix ending of -ite

• c. If it contains one less than the –ite anion, it is given the prefix of hypo- (CO-2 hypocarbonite)

• d. If it contains one more than the –ate ion, it is given the prefix of per- (CO4

-2 percarbonate)

• 4. The method for writing formulas with polyatomic ions is the same as with binary compounds, except the polyatomic ion name will be the cation or anion name

• a. polyatomic ions with positive charges are cations and are written first Ex. (NH4

+1)

• b. polyatomic ions with negative charges are anions and are written second

• c. if a subscript must be given to a polyatomic ion in a formula, then the polyatomic ion is placed in parenthesis first

• F. Naming Binary Molecular Compounds• 1. The new naming system is the Stock

system, which uses oxidation numbers• 2. The older system uses prefixes to indicate

the number of each atom in the molecule

• Mono (1) Di(2) Tri(3) Tetra(4) Penta(5) Hexa(6)• Hepta(7) Octa(8) Nona(9) Deca(10)

• G. Covalent Network compounds• 1. Some covalent compounds do not have

individual molecules, but instead, all the molecules are joined into a network (similar to ions in a crystal)

• 2. The subscripts in the formula represent the smallest whole number ratio of atoms

• H. Acids and Salts• 1. Binary acids – acids that • consist of two elements (HCl)• (hydrogen and a halogen)

• 2. Oxyacids – acids made of hydrogen, oxygen, and another nonmetal (hydrogen and a polyatomic ion) (H2SO4)

• Our use of the term acid really • means the acidic compound dissolved in water• 4. Hydrochloric acid is hydrogen chloride

dissolved in water• 5. Salt – a cation and an anion from an acid• 6. Some anions have the word • hydrogen or the prefix bi- added• to their name (bicarbonate)

• I. Naming Acids• 1. If the –ate form of the polyatomic ion is used in

the acid, then the acid’s name ends in –ic• 2. If the –ite form of the polyatomic ion is used in

the acid, then acid’s name ends in –ous• 3. If the hypo- or per- forms of the polyatomic

ion are used in the acid, then the acid’s name includes the prefixes

• Examples: sulfate – sulfuric acid• sulfite – sulfurous acid• perchlorate – perchloric acid• hypochlorite – hypochlorous acid