Chemistry Notes: Chapter 7
Formulas and Compounds
Writing Chemical Formulas—p. 203
Monatomic ions—Ions formed from a single atom.
Monatomic cations are identified with the element name.
Monatomic anions are named by dropping the ending and adding “ide” to the root name.
If an element has more than one charge or oxidation number, a Roman numeral follows
the name to designated which ion it is. (See p. 205)
Binary Ionic Compounds: Compounds composed of two different elements. To write their
formula: Follow the rules on page 206.
To name Binary Compounds—name the cation first and the name the anion—remember that the
anion’s ending has been changed to “ide”.
Oxyanions—polyatomic ions that contain oxygen.
In some cases, two different oxyanions are formed by the same two elements. When naming
these compounds, the most common ion is given the ending “ate”. The ion with one less oxygen is
given the ending “ite”.
Nitrate-NO3Nitrite: NO2If another compound is formed with even one less oxygen, the prefix “hypo” is added to the root.
An anion with one more oxygen than the “ate” anion is given the prefix “per”.
hypochlorite: ClO- chlorite: ClO2-
chlorate: ClO3-
perchlorate ClO4-
Compounds made from polyatomic ions are named the same as binary compounds. Name the
cation and follow with the anion.
Naming Binary MOLECULAR Compounds: The old system used prefixes to designate the
number of atoms present in the compound. Follow the rules on page 212.
Covalent Network Compounds: Compounds are name similar to molecular compounds. The
formula indicates the smallest whole number ratio of the atoms because there are no distinctive
units in the compound. Si3N4 trisilicon tetranitride or SiC silicon carbide.
Binary Acids—the acids that consist of two elements—usually hydrogen and one of the halogens.
Oxyacids—acids that contain hydrogen, oxygen, and a third element usually a nonmetal. Most
polyatomic ions are produced by the loss of hydrogen ions from oxyacids.
Salts: ionic compound composed of a cation (usually from a base) and an anion from an acid.
Sometimes the anion has retain one or more of the hydrogen atoms from the acid. In those cases,
the word hydrogen or the prefix “bi” is added to the anion name. HCO3- hydrogen carbonate
ion or the bicarbonate ion.
1
7-2 Oxidation Numbers
Oxidation numbers or states—a number assigned to an atom that indicates the general
distribution of electrons among bonded atoms. They are used in naming compounds, writing
formulas and in balancing chemical equations.
Rules for assigning oxidation numbers: p. 216
Practice problems: p. 218
Stock system of naming compounds: Uses Roman numerals to designate ionic charges. This
method is often used instead of using prefixes. P 219
7-3 Formula mass—sum of the average atomic masses of all the atoms represented in its formula.
The formula mass of water is 18.02 amu’s.
Molar mass—calculated by finding the sum of the masses of the elements present in a mole of the
molecule or formula unit. The molar mass of water is 18.02 grams.
Conversions using molar mass. (Factor Label Method) Practice problems p. 226
Percentage Composition: Gives the percentage by mass of each element in a chemical compound.
It is found by taking the mass of each element divided by the total mass of the compound x 100.
(p. 226)
7-4 Empirical Formula—
contains the symbols for the elements combined in a compound with subscripts showing the
smallest whole-number ratio of the atoms in the compound. One can calculate empirical
formulas from percentage composition data. P. 229
Molecular formulas—actual formulas of a molecular compound can by calculated by using the
empirical formula. The molecular formula is always a whole number multiple of the empirical
formula. P. 232
2