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 NH4

+) 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) Fe2+ & Fe(III) Fe3+

Monatomic anions (formed from nonmetals) use the stem of the element and add the suffix –ide. Oxygen becomes Oxide O2-, Nitrogen becomes Nitride N3-

The compound is then named cation first then anion Na+ + Cl- → NaCl named Sodium Chloride Fe2+ + O2- → FeO named Iron (II) Oxide 2 Fe3+ + 3O2- → Fe2O3 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 NH4

+

Polyatomic anions are negatively charged NO3

-

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. Ca2+ + SO4

2- → CaSO4 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. NH4

+ + Cl- → NH4Cl 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. Pb4+ + 2SO4

2- → Pb(SO4)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.

H2O dihydrogen monoxide……….also called water

CO2 carbon dioxide

CH4 carbon tetrachloride……….also called methane

NH3 nitrogen trihydride……….also called ammonia

N2O 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