How do the names of ionic compounds differ from covalent compounds?
1 Answer
The name of an ionic compound is
name of cation + name of anion (two words)
You will have to memorize the formulas of the common ions. One you have done that, you can follow the following rules to generate the names.
NAMING CATIONS
Cations that can have only one charge, such as Na⁺ and Mg²⁺ have the same name as the metal (sodium or magnesium). There is one common polyatomic cation — NH₄⁺ ammonium.
Transition metals form cations with more than one charge. To the names of these ions, we add the charge as a capital Roman numeral in parentheses.
Thus,
Fe²⁺ is iron(II); Fe³⁺ is iron(III); Cu⁺ is copper(I); Cu²⁺ is copper(II)
Note that there are no spaces between the letters and the parentheses.
NAMING ANIONS
a. Monatomic anions
The name of a monatomic anion is
stem of element name + ide
H⁻ hydride
F⁻ fluoride
O²⁻ oxide
S²⁻ sulfide
N³⁻ nitride
P³⁻ phosphide
b. Oxyanions
Oxyanions are polyatomic anions that contain oxygen. When an element forms two oxyanions, the one with less oxygen is given a name ending in -ite and the one with more oxygen is given a name that ends in -ate.
NO₂⁻ nitrite
NO₃⁻ nitrate
SO₃²⁻ sulfite
SO₄²⁻ sulfate
The halogens can form four oxyanions. In this case, the two in the middle use the ite and -ate suffixes. The one with the fewest oxygen atoms adds the prefix hypo-, and the one with the most oxygen gets the prefix per-.
ClO⁻ hypochlorite
ClO₂⁻ chlorite
ClO₃⁻ chlorate
ClO₄⁻ perchlorate
Some polyatomic oxyanions also contain one or two hydrogen atoms. We name these ions by adding the word hydrogen or dihydrogen in front of the name of the anion.
HCO₃⁻ hydrogen carbonate
HSO₄⁻ hydrogen sulfate
HPO₄²⁻ hydrogen phosphate
H₂PO₄⁻ dihydrogen phosphate
NAMING COVALENT COMPOUNDS
a. Binary covalent compounds
Binary covalent compounds contain only two elements. The less electronegative element is named first. They are named as
multiplying prefix+name of first element + multiplying prefix+name of second element (two words)
If there is only one atom of the first element, the multiplying prefix is omitted. Also, the final a of a prefix is omitted if the next letter is o.
The common multiplying prefixes are
1= mono; 2 = di; 3 = tri; 4 = tetra; 5 = penta; 6 = hexa; 7 = hepta; 8 = octa; 9 = nona; 10 = deca.
NO nitrogen monoxide
NO₂ nitrogen dioxide
N₂O₄ dinitrogen tetroxide [not tetraoxide]
b. Acids
Acids have two different names — a “compound name” and an “acid name”.
The compound is named as an ionic compound in which the cation is H⁺.
HCl hydrogen chloride
HClO₂ hydrogen chlorite
HClO₃ hydrogen chlorate
H₂SO₄ hydrogen sulfate
More frequently, and always when the compound is dissolved in water, we use the “acid name”. All these acids have the same cation H⁺, so we don’t need to name the cation. We simply change the ending of the name.
-ate becomes –ic acid
-ite becomes –ous acid
BUT, for binary acids, we also put hydro in front of the name.
-ide becomes hydro-…-ic acid
HCl hydrochloric acid
HClO₂ chlorous acid
HClO₃ chloric acid
H₂SO₄ sulfuric acid
SUMMARY
The names of ionic and covalent compounds follow similar principles:
They are usually two words.
The less electronegative atom is named first.
All you have to do is know the formulas and names of the ions.
