Nomenclature
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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

Some commonly used elements are listed below. Watch the spelling.

aluminum	Al	lead (plumbum)	Pb
antimony (stibium)	Sb	lithium	Li
argon	Ar	magnesium	Mg
arsenic	As	manganese	Mn
barium	Ba	mercury	Hg
bismuth	Bi	neon	Ne
beryllium	Be	nickel	Ni
boron	B	nitrogen	N
bromine	Br	oxygen	O
calcium	Ca	phosphorus	P
carbon	C	potassium	K
chlorine	Cl	radium	Ra
chromium	Cr	silver (argentum)	Ag
fluorine	F	sodium	Na
gold	Au	Sulfur	S
helium	He	tin (stannum)	Sn
hydrogen	H	uranium	U
iodine	I	zinc	Zn
iron	Fe

Names and symbols shown in blue often cause difficulties.

Some common elements are:

Valence Shell Electrons

Valence shell electrons are those electrons found in the outer energy level 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 the less electronegative to the more electronegative atom.  This is called ionic bonding.  The other extreme sees the electrons equally shared in a bond called a covalent bond.  This 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.

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.

When you are unsure of an element’s oxidation number, look it up on the periodic table.

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

Binary Compounds

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

To name a particular binary compound, the metallic element (found to the left of the steps on periodic table) is named first.

The non-metallic element (found to the right of the steps on periodic table) is then named, except that its ending is changed to "ide".

Example:

When writing formulae:

• For convenience, treat all compounds as ionic compounds, even though many are covalent.
• Compounds have no net charge. Therefore, positive and negative charges on ions have to balance one another.
  Example: MgCl₂ has one Mg²⁺ ion and two Cl^1-ions, hence no net charge.
• The positive ion in a compound is written before the negative ion.
  Example: sodium chloride has the formula NaCl

Write the chemical formula for:

Write the name of the following formulae:

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?

IUPAC SYSTEM

A naming system called the IUPAC system (International Union of Pure and Applied Chemistry) was developed to eliminate such difficulties.

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 brackets, after name of the element.

This method can be used to name any compound.

-OUS -IC SYSTEM

'IUPAC system' is not only system used for naming compounds containing elements with multiple oxidation numbers.

If bonding is between metal with two oxidation numbers and a nonmetal, an older system, still in use in naming of such compounds, is the -ous -ic system.

Where metallic element has only two oxidation numbers, the lower oxidation form has the ending 'ous' while the higher oxidation form has the ending 'ic'.

This naming method requires knowing Latin names of some of elements, namely:

• copper      cuprum
• iron            ferrum
• lead           plumbum
• tin              stannum

Examples:

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.

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.

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

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	_____________________________

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

“NICK the CAMEL ate CLAMs for SUPPER in PHOENIX”

Several other acids can be easily found by adding and subtracting oxygen atoms to/from the above oxy-acids. A summary of these acids is shown below.

Polyatomic anions may be obtained from above acids by removing H 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.

Table of Polyatomic Ions

When a polyatomic ions is part of chemical formula, the compound must still be electrically neutral. Charge supplied by polyatomic ion must balance the total opposite charges.

e.g. 3 Na+ balance PO₄^2-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

In addition to the polyatomic ions obtained from the oxy-acids, there are a number of others commonly found in chemistry.

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.