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

Nonmetals including H

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

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

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

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.

Class 3 prefixes - Memorize

Examples: Naming Class III CO 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

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

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

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