Ch 4 Names of Compounds  We will learn to name binary molecular compounds and both binary and polyatomic ionic compounds.  The most important skill is being able to identify the difference between molecular compounds and ionic compounds.  Recall that ionic compounds are a combination of metal and nonmetal. Molecular compounds are nonmetal and nonmetal. If more than two elements are present and a metal is listed first (or ammonium NH 4 + ) then the compound is ionic with a polyatomic ion.  Each of these three cases has a separate naming scheme.

Naming Binary Ionic Compounds  Monatomic cations take the name from the element that they were formed from.  Sodium forms the sodium ion Na → Na + + e-  Ions formed from elements that form more than one cation (transition metals) have a roman numeral following the name indicating the charge.  Iron forms two ions: Fe(II) Fe 2+ & Fe(III) Fe 3+  Monatomic anions (formed from nonmetals) use the stem of the element and add the suffix –ide.  Oxygen becomes Oxide O 2-, Nitrogen becomes Nitride N 3-  The compound is then named cation first then anion  Na + + Cl - → NaCl named Sodium Chloride  Fe 2+ + O 2- → FeO named Iron (II) Oxide  2 Fe O 2- → Fe 2 O 3 named Iron (III) Oxide

Ions – Polyatomic ions  Molecular groups can also be charged upon forming. These groups of many atoms (poly) are called polyatomic ions  Polyatomic cations are positively charged NH 4 +  Polyatomic anions are negatively charged NO 3 -  Polyatomic ions combine with monatomic ions or other polyatomic ions to form ionic compounds.

Table 4.4 in your book lists the more common polyatomic ions

Naming with Polyatomic Ions  A polyatomic ion will usually be listed second with the exception of the ammonium ion NH4 +.  Name the compound using the appropriate rule for the cation followed by the name of the polyatomic ion as listed on the chart.  Ca 2+ + SO 4 2- → CaSO 4 named Calcium Sulfate  If ammonium is the cation, use the monatomic anion naming scheme or, if combined with another polyatomic ion, use the name of the polyatomic anion.  NH Cl - → NH 4 Cl named Ammonium Chloride  If the polyatomic ion needs to be multiplied by a factor to neutralize the charge, be sure to place parenthesis around the whole polyatomic ion and use a subscript.  Pb SO 4 2- → Pb(SO 4 ) 2 named Lead (IV) Sulfate

Naming Binary Molecular Compounds  We will only learn the naming scheme for binary (that means two nonmetals) molecular compounds  We will not predict yet the way that nonmetals combine, we are only interested on learning their nomenclature  The first word is the name of the element preceded by a Greek prefix if more than one is present in the molecular formula  The second word is the stem of the second element listed with the suffix –ide added similar to anions. The second element is also preceded by a Greek prefix indicating the number of atoms present.  H 2 O dihydrogen monoxide……….also called water  CO 2 carbon dioxide  CH 4 carbon tetrachloride……….also called methane  NH 3 nitrogen trihydride……….also called ammonia  N 2 O dinotrogen monoxide…….. Also called nitrous oxide  Prefixes  1. mono  2. di  3. tri  4. tetra  5. penta  6. hexa  7. hepta  8. octa  9. nona  10. deca