Nomenclature Chemytry

Chapter 3

NOMENCLATURE

3.1 Introduction

Naming compounds may seem like a very complicated task, but if we look closely at the

names of compounds, we can discern that there is a system involved. Learning how to

name compounds then becomes a simpler task where we need to learn the system and

then how to apply it.

This system has been broken down into 9 topics. As with any other language, you will

need to practice in order to become fluent. Many websites will help you practice.

3.2 Naming Monoatomic Ions

A monoatomic ion is an ion composed of only one type of atom. The naming of

monoatomic ions depends on whether the ion is positive or negative.

Positive ions: These are named by simply taking the name of the element and adding the

word “ion” to form the ion name. For example, Na+ would be Sodium ion and Ca2+

would be Calcium ion.

Negative ions: These are named by taking the name of the element and changing the

ending to finish in –ide and then adding the word “ion”. For example Cl–

is Chloride ion

(Cl being Chlorine we change the –ine to –ide). Some names will be shortened more. For

example O2–

is Oxide ion and N3–

is Nitride ion. With a bit of practice these will come

naturally to you.

Elements having similar chemical and physical properties lie in vertical columns called

groups. The horizontal rows of the table are called periods.

3.3 The Periodic Table

The periodic table can be divided into several regions according to the properties of the

elements:

• metals

• metalloids

• non metals

Elements in a group generally react with other elements to form similar compounds. All

elements in a group have atoms with similar electronic structure. Here are some

properties for the most common groups:

Group 1A Alkali metals (except for H)

• very reactive

• react with water to produce H2 and alkaline solutions

• never found in free form in nature

• form A2O with oxygen

Group 2A Alkaline earth metals

• occur naturally only in compounds

• except for Be, react with water to produce alkaline solutions

• form EO with oxygen

Transition elements: periods 4-5-6

• metals

Lanthanides - follow lanthanum

Actinides - follow actinium

Group 7A Halogens

• combine violently with alkali metals to form salts

• among the most reactive of all elements

Group 8 Noble gases

• least reactive of all elements

• all gases

3.4 Naming Transition Metal Ions

Some elements can make more than one ion. For example, iron commonly makes the

Fe2+ and Fe3+ ions. Following the rules given above, both of these ions would be called

Iron ion. We cannot have two distinct chemical species with the same name. The

convention then is to add a roman numeral indicating the charge on the ion. Fe2+ is

therefore the Iron (II) ion while Fe3+ is the Iron (III) ion.

There is one notable exception to this: Mercury. Mercury makes two common ions both

having a charge of +2:

Hg2

2+ Mercury (I) ion

Hg2+ Mercury (II) ion

Many elements make several ions but you are only expected to know the most common ones.

3.5 Naming Simple Binary Compounds

Binary compounds are compounds composed of two monoatomic ions. It is important to

keep in mind that a compound must be electrically neutral. Any species that bears a

charge is an ion and will be named accordingly.

When combining a positive ion with a negative ion, the charges must cancel out and so

multiples of one or both ions may need to be used. For example, Ca2+ and N3–

. Simply

adding the charges would result with a non-neutral species so in order for the charges to

cancel out, we need to use three calcium ions and 2 nitride ions. The overall charges will

then be +6 and –6 and will cancel out to give the electrically neutral compound Ca3N2.

To name this compound we take the names of both ions, combine them and remove the

“ion” parts of the name: Calcium ion Nitride ion → Calcium nitride. You will notice

there is no need to mention in the name that there are 3 calcium ions and 2 nitride ions.

The fact that the compound is named as a compound (instead of an ion) implies it is

electrically neutral and must therefore contain the 3 calcium ions and 2 nitride ions.

Likewise, AlCl3 would be called aluminum chloride. But remember that transition metal

ions may need a roman numeral: FeCl2 would be iron (II) chloride.

3.6 Naming Binary Covalent Compounds

Covalent compounds are compounds made from non-ionic species. They are composed

of two non-metallic elements. To name these compounds, the first element is named as an

element and a prefix is used to indicate the number of atoms present. However, if there is

only one atom then no prefix is used. The prefixes are listed below:

One → mono

Two → di

Three → tri

Four → tetra

Five → penta

Six → hexa

Seven → hepta

Eight → octa

Nine → nona

Ten → deca

The second element is named as a negative ion again using the prefix to indicate the

number of atoms.