CHM 101 GENERAL CHEMISTRY

FALL QUARTER 2008

Section 2

 

Lecture Notes – 10/8/2008

(last revised: 10/7/08)

 

 

2.8          Naming Simple Chemical Compounds

  • Names and Symbols for the Elements
    • Most elements have symbols that are directly constructed from the names. For example:

Symbol is First Letter of Name

Hydrogen

H

Nitrogen

N

Oxygen

O

Fluorine

F

Symbol is First Two Letters of Name

Lithium

Li

Aluminum

Al

Silicon

Si

Bromine

Br

Symbol is First Plus Another Letter of Name

Chlorine

Cl

Chromium

Cr

Magnesium

Mg

Manganese

Mn
    • Some elements have symbols that are based on their original names instead of their current names. These require memorization:

Current Name

Original Name

Symbol

Antimony

Stibium

Sb

Copper

Cuprum

Cu

Gold

Aurum

Au

Iron

Ferrum

Fe

Lead

Plumbum

Pb

Mercury

Hydrargyrum

Hg

Potassium

Kalium

K

Silver

Argentum

Ag

Sodium

Natrium

Na

Tin

Stannum

Sn

Tungsten

Wolfram

W

 

  • Common Names for chemical compounds: Colorful, but not very informative.
    • sugar of lead
    • blue vitriol
    • oil of vitriol
    • quicklime
    • Epsom salts
    • milk of magnesia
    • gypsum
    • laughing gas
  • Need a system where the name says something about the composition.
    • Determine the name, given the formula, or…
    • Determine the formula, given the name.
  • Naming of Binary Ionic Compounds: These are compounds containing monatomic ions of two elements.
    • One of the components is a monatomic anion. The names of monatomic anions are based on the names of the elements, but the endings are changed to “-ide.” Note that the ions with -1 charges are all from Group 17 (except for hydride); those with -2 charges are from Group 16; and those with -3 charges are from Group 15 of the periodic table.
    • And, as an aid to learning, let’s mark our periodic tables to show the positions of each element that forms monatomic ions, with different colors for anions, Type I cations, and Type II cations.

Anion

Name

Group

H-

Hydride

1

F-

Fluoride

17

Cl-

Chloride

17

Br-

Bromide

17

I-

Iodide

17

O2-

Oxide

16

S2-

Sulfide

16

N3-

Nitride

15

P3-

Phosphide

15

 

 

 
    • The other component is a monatomic cation. There are two types of these ions. We consider first Type I, where the element forms only one kind of ion. Note that all of the cations from elements in Group 1 have +1 charges and that all the cations of Group 2 elements have +2 charges. Note also that the cations have names that are identical to the names of the elements.

Cation

Name

Group

H+

Hydrogen

1

Li+

Lithium

1

Na+

Sodium

1

K+

Potassium

1

Cs+

Cesium

1

Be2+

Beryllium

2

Mg2+

Magnesium

2

Ca2+

Calcium

2

Ba2+

Barium

2

Ag+

Silver

11

Zn2+

Zinc

12

Cd2+

Cadmium

12

Al3+

Aluminum

13

Ga3+

Gallium

13

 

 

 
    • Let’s pause here and name some Binary Ionic Compounds of Type I. Here are the rules:
      • There is always one kind of monatomic cation and one kind of monatomic anion.
      • The name of the cation comes first. The name of the anion comes second.
      • The net charge on an ionic compound is 0. This means that the numbers of ions of each type must be chosen so that the charges balance.
      • Some examples:

Compound

Ions Present

Name

NaCl

Na+, Cl-

Sodium chloride

KI

K+, I-

Potassium iodide

CaS

Ca2+, S2-

Calcium sulfide

Li3N

Li+, N3-

Lithium nitride

CsBr

Cs+, Br-

Cesium bromide

MgO

Mg2+, O2-

Magnesium oxide

Na2O

Na+, O2-

Sodium oxide

Al2O3

Al3+, O2-

Aluminum oxide

CsF

 

 

AlCl3

 

 

LiH

 

 

 

 

Cesium iodide

 

 

Lithium fluoride

 

 

Calcium phosphide

 

 

 
    • Now we consider Type II cations. These differ from Type I in that the metals that form them by ionization can form more than one kind of ion. Take iron (Fe) for example. There are two kinds of iron chloride:
      • FeCl2, which contains Fe2+ ions. The name for this is iron (II) chloride.
      • FeCl3, which contains Fe3+ ions. The name for this is iron (III) chloride.
    • The rules for naming Type II Binary Ionic Compounds are the same as for Type I, except that there is one additional rule. We use a roman numeral in the chemical name to indicate the charge on the cation.
    • Here is a list of common Type II cations. You need to memorize which charges go with which elements. Note also that mercury (I) always occurs as the diatomic ion, Hg22+.

Cation

Name

Group

Fe3+

Iron (III)

8

Fe2+

Iron (II)

8

Cu2+

Copper (II)

11

Cu+

Copper (I)

11

Co3+

Cobalt (III)

9

Co2+

Cobalt (II)

9

Sn4+

Tin (IV)

14

Sn2+

Tin (II)

14

Pb4+

Lead (IV)

14

Pb2+

Lead (II)

14

Hg2+

Mercury (II)

12

Hg22+

Mercury (I)

12

Cr3+

Chromium (III)

6

Cr2+

Chromium (II)

6

Mn3+

Manganese (III)

7

Mn2+

Manganese (II)

7

 

 

 
    • Now let’s try naming some Type II Binary Ionic Compounds:

Compound

Ions Present

Name

FeCl3

Fe3+, Cl-

Iron (III) chloride

FeO

Fe2+, O2-

Iron (II) oxide

CuI

Cu+, I-

Copper (I) iodide

CuO

Cu2+, O2-

Copper (II) oxide

CuCl

 

 

HgO

 

 

Fe2O3

 

 

 

 

Manganese (IV) oxide

 

 

Lead (II) chloride

 

 

Mercury (I) bromide

 

    • And let’s try naming some more Type I and Type II Binary Ionic Compounds:

Compound

Ions Present

Name

CoBr2

 

 

CaCl2

 

 

Al2O3

 

 

 

 

Chromium (III) chloride

 

 

Gallium iodide

 

  • Naming of Ionic Compounds Containing Polyatomic Ions:
    • The hard part is memorizing the formulas, the charges, and the names of the common polyatomic ions, but such memorization is absolutely necessary. Here is the list:

Cation

Name

NH4+

Ammonium

Hg22+

Mercury (I)

Anion

Name

NO2-

Nitrite

NO3-

Nitrate

SO32-

Sulfite

SO42-

Sulfate

HSO4-

Hydrogen sulfate

OH-

Hydroxide

CN-

Cyanide

PO43-

Phosphate

HPO42-

Hydrogen phosphate

H2PO4-

Dihydrogen phosphate

NCS-

Thiocyanate

CO32-

Carbonate

HCO3-

Hydrogen carbonate

ClO-

Hypochlorite

ClO2-

Chlorite

ClO3-

Chlorate

ClO4-

Perchlorate

C2H3O2-

Acetate

MnO4-

Permanganate

Cr2O72-

Dichromate

CrO42-

Chromate

O22-

Peroxide

C2O42-

Oxalate

 

 
    • Notes on these names:
      • The hydrogen sulfate ion is often called bisulfate, and the hydrogen carbonate ion is often called bicarbonate.
      • Many of these ions contain one or more oxygens. With several exceptions (hydroxide, acetate, oxalate) these are classed as oxyanions. Some elements form more than one kind of oxyanion. In that case, the suffix, -ite, is attached to the ion with the lesser number of oxygens and the ending, -ate, is attached to the ion with the greater number of oxygens. Good examples are sulfate (SO42-) and sulfite (SO32-). Some elements form as many as four kinds of oxyanion. In that case, the prefix, hypo-, and the suffix, -ite, are attached to the name of the ion with the lowest number of oxygens, and the prefix, per-, and the suffix, -ate, are attached to the name of the ion with the highest number of oxygens. The example in the above table is the series of oxyanions of chlorine.
    • Having memorized the formulas, charges, and names of these polyatomic ions, you should find it easy to assign names to compounds that contain them. The only new rule is that if a compound contains two (or more) of the same polyatomic ion, the formula of the ion is wrapped in parentheses, and the number is appended as a subscript after the right parenthesis. An example is ammonium sulfate, shown in the first line of the next table.
    • Here are some exercises to try (fill in the blanks):

Formula

Ions

Name

(NH4)2SO4

NH4+, SO42-

Ammonium sulfate

Na2SO4

 

 

KH2PO4

 

 

Fe(NO3)2

 

 

Mn(OH)2

 

 

Na2SO3

 

 

Na2CO3

 

 

 

 

Sodium hydrogen carbonate

 

 

Cesium perchlorate

 

 

Sodium hypochlorite

 

 

 
    • And here are two challenge exercises: (Hint: Use the periodic law to infer the formulas of the selenate and bromate ions.)

Formula

Ions

Name

 

 

Sodium selenate

 

 

Potassium bromate

 

 

 
  • Naming Binary Covalent Compounds (The text calls these also Type III binary compounds)

o       Binary covalent compounds are formed between two non-metals. The rules for naming them are very similar to the rules for binary ionic compounds, even though their bonds are covalent rather than ionic.

o       The first element in the formula is named first, using the full name of the element.

o       The second element is named as if it were an anion.

o       Prefixes mono-, di-, tri-, etc., are used to indicate the numbers of each type of atom. See Table 2.6 in your text for a full list.

o       The prefix, mono-, is never applied to the first element in the name. For example, CO is carbon monoxide, and CO2 is carbon dioxide.

o       The letters, o, and a, on the ends of prefixes can be omitted to avoid awkward pronunciations if the name of the following element begins with a vowel. Examples: carbon monoxide and phosphorous pentoxide.

o       Water and ammonia are always referred to by their common names, never by their systematic names based on the formulas, H2O and NH3.

o       Some examples for class discussion:

Formula

Name

H2O

Water

NH3

Ammonia

N2O

Dinitrogen monoxide

NO

Nitrogen monoxide

NO2

Nitrogen dioxide

N2O3

Dinitrogen trioxide

N2O4

Dinitrogen tetroxide

N2O5

Dinitrogen pentoxide

PCl5

 

PCl3

 

SO2

 

 

Sulfur hexafluoride

 

Sulfur trioxide

 

Carbon dioxide

 

 
  • Summary: How to Name Binary Compounds

o       Here is the flowchart from your text (Figure 2.23). (In the text, binary covalent compounds are also called Type III binary compounds):

o       Another flow chart (Figure 2.24) from your text expands the naming process to encompass compounds containing polyatomic ions:

o       The following examples cover the naming of all the types of compounds we have discussed in this set of notes. You should be able to use the periodic table to deal with any ion whose name and formula you have not been asked to memorize.

Formula

Name

P4O10

 

Nb2O5

 

Li2O2

 

Ti(NO3)4

 

 

Vanadium (V) fluoride

 

Dioxygen difluoride

 

Rubidium peroxide

 

Gallium oxide

 

 
  • Names of Acids

o       Acids are so important that three entire chapters of your text (Chapters 4, 14, and 15) are devoted to them. Here we will confine the discussion to a brief definition of acid and to some rules for naming acids.

o       Acids are substances that, when dissolved in water, will produce hydrogen ions (H+). An acid can be pictured as a molecule with one or more protons (H+) attached to an anion.

o       How to name acids:

§         If the anion does not contain oxygen, the acid’s name includes the prefix, hydro-, and the suffix, -ic. The word, “acid,” follows. For example, HCl contains a chloride anion, (Cl-), and is named Hydrochloric acid. The most important acids of this class are listed in Table 2.7 from the text.

§         If the anion does contain oxygen, and the name of the anion ends in “–ate,” the suffix, “-ic,” replaces the “-ate,” and the word, “acid,” follows. For example, H2SO4 contains a sulfate anion (SO42-), and is named sulfuric acid.

§         If the anion contains oxygen and the name of the anion ends in “-ite,” the suffix “-ous,” replaces the “-ite,” and the word, “acid,” follows. For example, H2SO3 contains a sulfite anion (SO32-), and is named sulfurous acid. Some examples of oxygen-containing acids are listed in Table 2.8.

§         The oxyacids of chlorine illustrate these rules:

§         A flowchart for the naming of acids is given in the text (Figure 2.25).