1. CLASS 3 COVALENT BONDS BETWEEN TWO NONMETALS
SO3 sulfur trioxide
CO2 carbon dioxide
CLASS 3 COVALENT BONDS BETWEEN TWO NONMETALS
“Prefixes”
N2O4 Dinitrogen tetroxide

2. Nonmetals including H

3. Classes I and II form ionic bonds; Class 3 forms covalent bonds

4. Location of First Element in Formula determines class rules+1
Class or Type I +2 +3
Class or Type II
Class or Type III +1 +2

5. 3 Sets of Rules of Naming Rules
Class or Type I - Ionic Bond between metal predictable + charge and a negative nonmetal or polyatomic ion ; name cations, anion ends in “ide”
Examples: NaCl – sodium chloride ; MgCl2, magnesium chloride
Class or Type II- Ionic Bond with variable oxidation state transition metal; Roman numerals used to specify charge of transition metal
Example: CuCl2 – copper(II) chloride
Class or Type III – Covalent bonds between Two nonmetals; uses prefixes
Example: CO2 – carbon dioxide; N2O4 – dinitrogen tetroxide

6. Rules for Naming Class 3 Compounds
First element in formula is named first. (First element is generally further to left on periodic table. If two nonmetals are in the same column element further down is generally written first.)
Second Element always ends in “ide”.
Prefixes are used to denote # of atoms present.
First element prefix only if more than 1 atom present (i.e. no mono prefix on first element); Second element always has prefix.

7. Class 3 prefixes - Memorize

8. Examples: Naming Class IIICO
Carbon monoxide
Note for –oxide preceded by o or a, drop o for easier pronunciation.
CO2
Carbon dioxide
N2O4
Dinitrogen tetroxide
Note prefix for N because more than 1 N

9. Practice Class III – Name each of the following
BF3
boron trifluoride
CCl4
carbon tetrachloride
O2F2
dioxygen difluoride

10. Writing Formulas for Class III
Translate prefixes exactly – DO NOT SIMPLIFY
No “criss-crosses” because NO IONS
Ionic compounds such as NaCl exist in lattice consisting of trillions of ions; formula is simplest ratio
The formula for covalently bonded molecules
represents the actual ratio of atoms

12. Practice Naming Class III compounds
tetraphosphorous hexoxide
P4O6 (do not simplify)
Xenon tetrafluoride
XeF4
Sulfur trioxide
SO3 (NOT polyatomic ion, sulfite, no charge present)