Chapter 7 – Chemical Formulas and Chemical Compounds

 

Nomenclature*
 “a naming system”

* Ionic compounds have different rules than covalent compounds

 

VOCABULARY

•         Monatomic ions

–        An ion formed from a single atom

•         Polyatomic ions

–        A charged group of covalently bonded atoms

•         Binary compounds

–        A compound composed of two different elements

•         Stock System (Roman numerals)

–        A system used to name elements with more than one possible charged ion

 

Symbols

language of chemistry

One or two letters - first is capitalized

Not all from English name of elements

Good Idea to Memorize Table 7-1 on page 205

 

Chemical Formulas

what atoms and how many of each

Symbols and subscripts( number of atoms)

 

H2O

H2=2 atoms of hydrogen

O = 1 atom of oxygen

Rules

1. Represent each element with the correct symbol

2. Use subscripts to indicate number of atoms of each element in compound, if one, do not use subscript

3. Write symbol of more metallic element first

 

Naming Binary Compounds

compounds made of 2 elements

1. Name the elements in the same order that they appear in formula

2. Drop the last syllable in the name of the final element and add -ide

 

Ionic compounds

formulas and names

Use ionic charge to predict formulas. Overall charge should be ZERO

1. Ions formed from elements in Group 1 have a charge of 1+

2. Ions formed from elements in Group 2 have a charge of 2+

3. Aluminum ions have a 3+ charge. Other elements in group 13 normally have a 3+ charge but the are EXCEPTIONS

4. Elements in other groups form ions with various charges

a. nitride ion 3- charge

b. sulfide ion 2- charge

c. oxide ion 2- charge

d. halogen ion 1- charge

 

Al2O3

 

Formulas with Polyatomic Ions

several atoms joined together to form ions

Table 7-2 (p210) in text

polyatomic ions react as individual ions in molecules

1. Find charge, balance charges

2. Place parentheses around ion before writing subscript

 

Naming Ionic Compounds

Name the ions in the compounds

Negative ions end in - ide

polyatomic ions use the name in the tables

 

Predicting Ion Charge (Stock System)

iron(II)chloride             iron(III)chloride

FeCl2                                       FeCl3

 

 

Naming Binary Molecular Compounds

 

•         Unlike ionic compounds, molecular compounds are composed of individual covalently bonded units, or molecules.

•         The prefix system can be used to name these molecules

–        The less electronegative element is given first

–        It is given a prefix only if it contributes more than one atom to the molecule

–        The second element is named by combining

–        The prefix indicating the number of atoms contributed by the element

–        The root of the name of the second element

–        The ending –ide (with few exceptions, the –ide means the compound contains only 3 elements

–        The o or a at the end of a prefix is usually dropped when the word following the prefix begins with another vowel

 

 

 

Binary Compounds of nitrogen and oxygen

 

Formula

Prefix-system name

N2O

dinitrogen monoxide

NO

nitrogen monoxide

NO2

nitrogen dioxide

N2O3

dinitrogen trioxide

N2O4

dinitrogen tetraoxide

N2O5

dinitrogen pentaoxide

 

 

Acids and Salts

 

  1. Binary acid – contain two elements
  2. Oxyacids – contain hydrogen, oxygen and a third element – usually a nonmetal

 

  1. Salt – an ionic compound composed of a cation and the anion from an acid
  2. Some salt contain anions in which one or more hydrogen atoms from the acid are retained. 
    1. The best known such anion comes from carbonic acid. 
    2. ( HCO3- named hydrogen carbonate ion or bicarbonate ion)

 

 

Covalent network compounds

 

•         Some covalent compounds do not consist of individual molecules.  Instead, each atom is joined to all its neighbors in a covalently bonded, three-dimensional network.  Naming such compounds follows similar rules as for molecular compounds.

–        Examples are:

•         SiC        silicon carbide

•         SiO2       silicon dioxide

•         Si3N4 trisilicon tetranitride

 

Naming Binary Molecular Compounds

Numerical prefixes

1        mono-              7          hepta-

2        di-                    8          octa-

3        tri-                    9          nona-

4        tetra-                10        deca

5        penta-

6        hexa-