Nomenclature

Introduction

This section will briefly outline the knowledge that will aid you in naming a few simple inorganic compounds.  In order to understand chemical names, we will also need to understand several concepts of chemistry itself, including but not excluded to terms like: oxidation numbers, valence electrons and valence.  These are briefly introduced here but are revisited in more detail later in the course.

The naming of chemical compounds is often known as nomenclature (accent on the syllable 'men').   Before we can name a compound made up of multiple elements, we must learn to name the elements themselves.  A list of commonly used elements is shown below. A complete list of chemical symbols may be found on the periodic table of the elements. Keep in mind that when the element symbol has two letters in it, they are always an upper case followed by a lower case letter.

e.g. The symbol for tin is Sn, not SN or sn or SN

When you write out the name of an element, you do not require a capital letter at the beginning of the name.

e.g. Sb is antimony not Antimony

Generally, the chemical name is taken from the name of the compound itself.  Sometimes, the latin name is used, often because when the particular element was first named, the english name was not in common use. In some cases, the first letter alone (carbon, oxygen, nitrogen, ...) sometimes the first and second letters, (neon, nickel,...) sometimes the letter starting the first and the second syllables (lead [plumbum], silver [argentum], antimony [stilbium], neodymium,... ).  As you can see, there is no simple rule so you will simply have to memorize the names that you will need.

Some commonly used elements are listed below. Watch the spelling.  In a few cases, the latin name for the element is used in the symbol lettering.  For example, lead has the chemical symbol Pb from the latin plumbum (think plumbing since originally, plumbing was done with lead pipes).  Thus, the latin name is given in parentheses in cases where the chemical symbol lettering comes from the latin rather than the English name. Actually, Latin was the language of higher learning for many hundreds of years and so all early compounds were given latin names.  Most of our English names still use lettering that is close to consistent with the original latin so most of the times, the letters are the same.  In a few cases, like iron (ferrum), lead (plumbum), etc. our english names are not the same as the latin names and hence the different letters.  Other languages, such as French or Spanish, still use latin names as their element names extensively and don't have as big a problem.

 

aluminum Al lead (plumbum) Pb
antimony (stibium) Sb lithium Li
argon Ar magnesium Mg
arsenic As manganese Mn
barium Ba mercury (hygrargyrum) Hg
bismuth Bi neon Ne
beryllium Be nickel Ni
boron B nitrogen N
bromine Br oxygen O
calcium Ca phosphorus P
carbon C potassium (kalium) K

chlorine

Cl

radium

Ra

chromium Cr silver (argentum) Ag

fluorine

 F sodium

Na

gold (aurum) Au sulfur S
helium He tin (stannum) Sn
hydrogen H uranium U
iodine I zinc Zn
iron (ferrum) Fe

Names and symbols shown in blue often cause difficulties.

Some common elements are:

Back to Top

Valence Shell Electrons  

Valence shell electrons are those electrons found in the outer energy levels of an atom and are the only electrons capable of bonding. The bonding type depends on the extent to which bonding electrons are shared.  In one extreme, electrons are not shared at all but are transferred wholly from one element (generally, the metal) to the a different atom (generally, the non-metal).  This is called ionic bonding.  The other extreme sees the electrons equally shared in a bond called a covalent bond.  This latter type only occurs in homonuclear diatomic molecules.  In all others, the bonding is somewhere in between the two extremes.

Bonding type may be determined by studying Lewis Structures and electronegativity values, as we'll see later.

The most common number of valence shell electrons "involved in bonding" may be found using this guide. These numbers correspond to oxidation numbers shown on the periodic table or to the number of unpaired valence shell electrons in an element.

Group IA IIA IIIB IVB VB VIB VIIB VIII
Common ionic charge  +1 +2 +3 +4 -3 -2 -1 0

The positive sign indicates that if an ion was formed during bonding, electrons would be lost by the element and the resulting ion formed would take on a positive charge.

The negative sign indicates that if an ion was formed during bonding, electrons would be gained by the element and the resulting ion formed would take on a negative charge.

The positive and negative charges would result only if ions are formed. Oxidation numbers give chemists a method of keeping track of electrons.

Generally, you can only determine an element's oxidation number by comparing it with the other elements to which it is bonded.  However, many elements have predominantly one particular oxidation number and simple rules can be used to determine its oxidation number.  When you are unsure of an element�s oxidation number,  One method is to look it up on the periodic table.  Locate the column it is in and then you can determine it's normal oxidation number.

Example: What are oxidation numbers of F, Ca, S, Fe?

The first three can be quickly determined from their column location in the periodic table. 

F is in column VIIB and has OX# = -1
Ca is in column IIA and has OX# = +2
S is in column VIB and has OX# = -2 (like Oxygen).  However, if S and O are bonded together then O will get the electrons (It attracts electrons more strongly than S, see the course section on electronegativity) and the S will end up being positive, not negative.

A more complete list of rules can be found in the course section "Assigning Oxidation Numbers"

This works well for main group elements but transition metals, like Fe are not so simple.  There, oxidation numbers don't follow quite as simple a set of rules.  For example, Fe has two common oxidation numbers (+2; ferrous, and +3 ferric) but it also has others (+4 and +5 in the biologically important cytochrome P450)  Similarly, the rules for counting electrons in transition metal complexes are not the same as for main group compounds.  In this course, we will mostly be worried about main-group compounds with only a few transition group compounds that you can memorize.

Back to Top
 

Binary Compounds

A binary compound is a compound formed from two elements only. The name of any binary compound ends in "ide".

If our binary compound is ionic (metal bonded to a non-metal), and if the metal has only one oxidation state, we can name them using simple rules. 

The metallic element (found on lower left of the periodic table) is named first.

The actual oxidation number can be determined from the column in the periodic table.  Column 1 had OX# = +1, Column 2 has OX# = +2.  transition metals generally have more than one oxidation state and are not named using these simple rules.

The non-metallic element (found to the upper right of the periodic table) is then named, except that its ending is changed to "ide". The ide ending means that element holds the negative oxidation number (negative charge in the pure ionic limit).

The oxidation number on the non metal can also be determined from the column in the periodic table.  elements in column 7 will have OX# = -1,  in column 6, OX# = -2, in column 5 it is -3 and anything else rarely forms ionic compounds.

Example:

NaCl sodium chloride
KBr potassium bromide

When writing formulae:

Write the chemical formula for:

a) potassium chloride ________________________________ Answers
b) sodium oxide ________________________________
c) aluminum fluoride ________________________________
d) copper oxide ________________________________
e) iron chloride ________________________________

Write the name of the following formulae:

f) CaO ________________________________ Answers
g) BaI2 ________________________________
h) Rb2O ________________________________
i) Hg20 ________________________________
j) HgO ________________________________

Notice that d) and e) above have two formulae each. These two answers are easy to distinguish when looking at the formulae. However, we must be able to distinguish them by name.

Similarly, i) and j) have two different formulae yet they have the same name.

How do we eliminate these ambiguities?

Back to Top

-OUS -IC SYSTEM

This system was used in compounds containing a metal with more than one oxidation number and a nonmetal.  The simple binary naming system would not work because the different oxidation numbers gave different binary compounds with the same metal/non-metal pair.  Metals in the first two columns of the periodic table have only one oxidation state and so will work find with the simpler rules discussed above.  Other compounds cannot use the simple binary rules. For example; FeCl2 and FeCl3 are both binary compounds between iron and chlorine.  Unfortunately, since iron had two different possible oxidation numbers, (+2) and (+3), respectively in these two compounds, we cannot name them both iron chloride since we need a unique name for each compound. 

One early system for naming such multi-oxidation number metals uses sufixes like 'ic' and 'ous' to indicate oxidation state of the metal.  Generally,  this system was developed back in the days when latin predominated as the language of science so the element names are the latin ones.  Hence, Fe2+ is ferrous and Fe3+ is ferric.  This system was applied to several of the early-known transition metals and still is used to this date in a few common compounds.  This system is largely superseded by other more versitile naming systems for the myriad of modern compounds that are known today.

Other elements that use the 'ic' 'ous' system include copper, lead, mercury, tin. 

In this case, the 'most common' oxidation number must be memorized.  For example, in iron, it is the 3+ oxidation state that is most common. Thus, any compound with iron (3+) must be named using the 'ic' suffix.  So FeCl3 is ferric chloride.  The next lower common oxidation form of the metal has the ending 'ous'.  Thus, FeCl2 is called ferrous chloride.

This naming method requires knowing Latin names of some of elements.  Here is a table of a few common metals and their oxidation numbers and names, which you may encounter in books and articles in your future studies.  This course will not rely on or test your knowledge of these but you should be able to recognise them for easier understanding of your reading in the future.

We can see in this table a problem.  The higher oxidation number in the 'ic' named element is not consistent and worse yet, the lower oxidation number is not always one lower.  In lead, it is two lower than the higher one.   The final blow to widespread use of this system involves the problem that many transition metals have mor than two oxidation states (for example Vanadium has 4 different states as found in VO, V2O3, VO2, V2O5.)

 This system largely relies on memorization of the names for each element.  It will not be used in this course except in the most casual of ways and in any exam, you will always be given both the name and the formula so that you cannot loose marks for not having memorized this.  That said, you will encounter it in your readings so let's try a few examples.

Examples:

Cu2O is _________________ Answers
Plumbic sulfide is _________________
FeCl2 is _________________
Stannous nitride is __________________
Back to Top

IUPAC SYSTEM

A more generally used naming system called the IUPAC system (International Union of Pure and Applied Chemistry) was developed, which is completely general and does not require ambiguous memorized sufixes on element names.

If you are naming a chemical compound from a formula, and first element in the formula has more than one oxidation number, the oxidation number for this multi-valent element is placed as a Roman Numeral, in parentheses, after name of the element.

This method can be used to name any binary ionic compound but in the case of mono-valent metals it is redundant and so not used.

copper (I) oxide is __________________ answers
Hg3N is __________________
FeCl2 is __________________
iron (III) sulfide is __________________
MgO __________________
Back to Top

PREFIX SYSTEM

Third way of naming compounds is prefix system . This method is almost always used when bonding occurs between two non-metals. To use this method you do not require oxidation numbers but must know following prefixes.

mono1
di 2
tri 3
tetra 4
penta 5
hexa 6
hepta 7
octa 8
nona 9
deca 10

When naming, place prefix indicating number of each type of atom in formula before the name of each element. Second element again has its ending changed to -'ide'. If the prefix 'mono' appears in front of first nonmetal, it may be omitted.

thus, using this scheme, we would name CO2 as carbon dioxide and CO as carbon monoxide.

Name each of the following. Where applicable, give two names.

1. ZnS _______________________________________________
Answers
2. FeO _______________________________________________
3. Sb2S3 _______________________________________________
4. CaCl2 _______________________________________________
5. BaO _______________________________________________
6. CuBr2 _______________________________________________
7. HgCl2 _______________________________________________
8. H2O _______________________________________________
9. PBr3 _______________________________________________

Write the formulae for each of the following.

    sodium chloride  _____________________________ answers
    calcium bromide _____________________________
    ferrous sulfide _____________________________
    copper (II) iodide _____________________________
    cuprous selenide _____________________________
    manganese (II) oxide _____________________________
    stannic sulfide _____________________________
 Some people have had fun with the names thusly derived.  Look at the humorous DHMO web site (http://dhmo.org) , perporting to be a genuine research division. 
Back to Top

Compounds with Polyatomic Ions:

Not all compounds are binary. This can easily be noticed by flipping through a chemistry book and noting the names of many compounds not ending in 'ide'.

Compounds not binary, generally contain a polyatomic ion consisting of a number of atoms. which hang around as a group. The group remains unchanged during a chemical reaction, and has a single oxidation number.

Key to remembering many of polyatomic ions is knowing the five oxy-acids listed below. They will unlock thousands of chemical formulae to you.

OXY-ACIDS

nitric acid HNO3  
carbonic acid H2CO3  
chloric acid HClO3  (iodic HIO3, bromic HBrO3)
sulphuric acid  H2SO4  (selenic H2SeO4, telluric H2TeO4)
phosphoric acid H3PO4

These five oxy-acids can be memorised using the memory tool �Nick the Camel ate Clams for Supper in Phoenix�, where the chemical symbol matches the underlined letters in the words.  Note that other acids in the same family can be identified quickly.  Thus for example, chlorine an be replaced by bromine or iodine (but not fluorine) to make other oxy-acids.

Additional other acids can be easily found for each entry here by adding and subtracting oxygen atoms to/from the above oxy-acids. A summary of these acids is shown below. Thus, we could have HNO, HNO2, HNO3.  The key to naming these is in memorizing the 'normal' number of oxygens and using the 'ic' ending for that compound (chloric acid is HClO3).  Any acid with one less oxygen uses the 'ous' ending (chlorous acid is HClO2).  If two less oxygens are used the prefix 'hypo' (below) is used with the 'ous' ending (hypochlorous acid is HClO). If one extra oxygen is used the prefix 'per' (above) is used with the 'ic' ending (perchloric acid is HClO4)

Here are a few examples.  Can you fill in the chemical formulae in the blank spaces in this table?
Hypo_ous Acid ous Acid   ic Acid  Per____ic Acid
HClO HClO2 HClO3 HClO4
___ HNO2 HNO3 ___
___ H2SO3 H2SO4 ___
___ H2CO2 H2CO3 ___
___ H3PO3 H3PO4 ___
<-------- Subtract an O Add an O -------->
Answers

Examples of Acids: HClO is hypochlorous acid
  phosphorous acid is H3PO3
  HClO4 is perchloric acid
  tellurous acid is H2TeO3
  HIO2 is iodous acid
  selenic acid is H2SeO4

Polyatomic oxy-anions may be obtained from above acids by removing the H atoms from first part of formula. Oxidation number for polyatomic ion is equal in number to number of H's found in the acid. A table of the polyatomic ions obtained from above acids is shown below.

Can you determine the correct formulae for these common polyatomic oxy-anions.

Table of Polyatomic Ions

Hypo_ite ite   ate  Per____ate
ClO- ClO2- ClO3- ClO4-
___ NO2- NO3- ___
___ SO32- SO42- ___
___ CO22- CO32- ___
___ PO33- PO43- ___
<-------- Subtract an O Add an O -------->
Answers

When a polyatomic ions is part of chemical formula, the compound must still be electrically neutral. You must balance the charge supplied by polyatomic ion by adding the appropriate number of positive ions (metals).

e.g. the compound socium phosphate needs 3 Na+ ions to balance PO43- to give us Na3PO4

Write a formula for each of the following:

  1. sodium sulphite
  2. magnesium carbonate
  3. aluminum hypochlorite

Give the name of each of the following:

  1. HNO2
  2. Ca3(PO3)2

Answers

In addition to the polyatomic ions obtained from the oxy-acids, there are a number of other ions commonly found in chemistry.  You will encounter these ions from time to time and should know what they are.

NAME FORMULA OF ION "OXIDATION NUMBER"
hydroxide OH- 1-
ammonium NH41+ 1+
acetate CH3COO- (C2H3O2-) 1-
permanganate MnO4- 1-
chromate CrO42- 2-
dichromate Cr2O72- 2-
bicarbonate HCO3- 1-
bisulfate HSO4- 1-
cyanide CN- 1-
thiocyanate SCN- 1-
oxalate C2O42- 2-
Write the formula for each of the following:
  1. potassium acetate
  2. ammonium oxalate

Write the name of each of the following:

  1. CuCr2O7
  2. Fe(SCN)3

    Answers

 

Worksheet on Nomenclature

Answers to Worksheet

This section and the accompanying work sheets are courtesy of Bill Newstead.

Back to Top