Download Unit 3: Bonding and Nomenclature Content Outline: Writing and

Unit 3: Bonding and Nomenclature
Content Outline: Writing and Naming Molecular Compounds and Acids (3.7)
I.
Molecular Compound
A. This is a compound composed of individually covalently bonded atoms, units, or molecules.
B. These can be named (nomenclature) in one of two different ways:
1. Stock Method
a. This system uses the elements or polyatomic molecules oxidation numbers/state.
2. Prefix system
a. This system uses prefixes to indicate the number of atoms, of each kind, within a molecule.
b. Prefixes: 1 –mono
4 – tetra
7 – hepta
10 - deca
2 – di
5 – penta
8 – octa
3 – tri
6 – hexa
9 – nona
II. Stock System (Oxidation number)
A. Oxidation number/state
1. This term refers to the number of electrons that must be added to or removed from an atom in a
combined state to convert the atom into the elemental form.
a. Indicated the distribution of electrons among bonded atoms.
B. Assigning Oxidation numbers to atoms or polyatomic groups.
1. As a rule, shared electrons go to the more electronegative atom.
2. Additional Rules:
a. Atoms in a pure element have oxidation numbers = 0.
b. The more electronegative element in a binary (2) compound is assigned it’s anion charge; the
least electronegative element gets assigned it’s cation charge.
c. Fluorine, the most electronegative element, is always assigned an oxidation number = -1.
Remember, your Periodic Trends for electronegativity on the Periodic Table? As you go
across a period they increase; as you go down a column/group they decrease.
d. Oxygen is always assigned -2 unless with Fluorine. If Fluorine is present, the Oxygen is
assigned +2.
You must always check for Fluorine, if you see Oxygen.
e. Hydrogen is always assigned +1 unless it is paired with a metal. If it is with a metal, then it is
assigned -1.
Know your metals by being able to look at a Periodic Table quickly. Remember, there are
metals, metalloids, and non-metals.
f. Neutral compounds equal zero.
g. Polyatomic ions are assigned oxidation numbers equal to the charge of the group.
Know those common polyatomic ions to make your life in Chemistry class easier.
h. This system can also be used with ions.
C. Naming compounds (molecular or ionic) using oxidation numbers:
1. This method of nomenclature will use Roman numerals for cations
2. Step 1: Use your chemical Formula.
Step 2: Write the cation name. First letter is capitalized
Step 3: Look at the subscript of the anion.
Step 4: Look at the subscript of the cation.
Step 5: Make the charges of each equal out to zero net charge (neutral). It may involve a little
math… adding or dividing.
Step 6: Write the numeral used to balance the cation charge with the anion charge as a Roman
numeral after the cation name. Such as Iron (II) or Lead (IV)
Step 7: Write the anion name after the Roman numeral. First letter is lower case.
Remember, to drop the ending and add the ending “ide”.
For example, PCl3  Cl = -1 so P must be +3 to equal zero; therefore, it is
Phosphorus (III) chloride.
N2O  O = -2 (no Fluorine present) so N2 (each must be 1); therefore, it is
Nitrogen (I) oxide.
Mo2O3  O = -2 (no Fluorine present) so -2 x 3 = -6; 2 Mo so 6/2 = 3 therefore
Molybdenum (III) oxide
III. Prefix System (numbers)
A. This system of naming use the prefix to identify the number of atoms present.
B. Step 1: The Element with the smaller group (column) goes first.
 If both elements come from the same group, then the highest energy level (row) goes
first.
Step 2: If only 1 atom is present, just use the element’s name.
If more than 1 atom is present, you must add the prefix to the elements name.
For example, 1 Hydrogen present  Hydrogen Chloride (HCl)
3 Hydrogens present  Trihydrogen Antimonide (H3Sb)
2 Sodium & 2 Oxygen  Disodium Dioxide (Na2O2)
Step 3: Drop the ending on the anion and replace with “ide”.
 DO NOT confuse the steps with your polyatomic ion rules.
C. If a prefix ends with an “o” or an “a” and the word following begins with a vowel, drop the “o” or “a”
from the prefix.
D. If both elements in the compound are non-metals the first named element is decide based upon this
sequence: (First)C P N  H  S I Br  Cl O  F (last possible)
This is an easy way to remember the sequence:
C.P. Newton & H.S. Igor brought Cauliflower to the party.
IV. Naming Acids
A. Acid
1. This is a substance that generates Hydrogen Ions (H+) when placed in a solution.
a. The Chemical Formula usually begins with H. Exception Acetic Acid  CH3OOH
b. There are basically two types of acids:
i. Binary Acids (2 elements present)
α. One element is Hydrogen.
β. The second element is a Halogen(Group 17).
ii. Oxyacids (3 elements present)
α. One element is Hydrogen.
β. The second element is Oxygen.
γ. The third element is a non-metal or polyatomic ion.
B. Naming:
1. Step 1: Do you have a monatomic anion or a polyatomic anion.
Step 2: If monatomic, - write “hydro” in front of the anion name.
For example, HCl Hydrochloric
If polyatomic, - use the polyatomic ion naming rules for the anion.
For example, H3PO4  Phosphoric
* The Hydrogen is not mentioned.
Step 3: If monatomic, replace “ide” with “ic” and add the word “acid”.
If polyatomic, replace “ite” with “ous” OR “ate” with “ic”
* Don’t forget your prefix, if needed… Hypo or Per
For example, HClO  Hypochlorous Acid
HClO2  Chlorous Acid
HClO3  Chloric Acid
HClO4  Perchloric Acid
C. Salt
1. This is an ionic compound composed of a cation and an anion from an acid.