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Inorganic Chemical Nomenclature



Before a systematic method of naming different chemical substances was established, various compounds were named after people, places, or things. Some examples would be washing soda (sodium carbonate, which is used for softening wash water), and Glauber's salt (sodium sulfate, discovered by J.R. Glauber). Because of the vast number of compounds known to man, numbering into the millions, a system of naming was devised to prevent total confusion from occurring. Chemical nomenclature is the systematic naming of chemical compounds.

Compounds can be divided into two basic categories, those which are true binary compounds (they contain only two types of elements), and those which contain more than two different types of elements. There is also a system of naming for organic (carbon-based) compounds.




Naming of Binary Compounds

A binary compound is a compound that consists of a combination of two elements. Compounds that end in IDE indicate that they contain only two elements. The first element is usually a positively charged metal, and the second element is usually a negatively charged nonmetal. The positively charged ion is the name of the metal, while the negatively charged ion consists of the stem plus the suffix IDE.


Stems of the most commonly used elements:

Element

Stem

oxygen

ox

chlorine

chlor

carbon

carb

iodine

iod

bromine

brom

selenium

selen

nitrogen

nitr

phosphorus

phosph

fluorine

fluor

sulfur

sulf or sulfur

These stems are placed in the second part of the binary compound's chemical name, before the ide. Here are some examples using the element stems and the suffix ide.




CaO is calcium oxide

CaO is calcium oxide because you have a calcium atom bonded to an oxygen atom. Since this is a binary compound (meaning that it is a compound comprised of only two elements) there is a positive and a negative ion. The positive ion is calcium, because it is a metal,so the oxygen is the negative ion. Now we write calcium as the name of the metal, and ox as the prefix of the second word (because oxygen's stem is ox). Lastly, we attach the suffix ide behind the ox to get the name calcium oxide.


AlN is aluminum nitride

AlN is aluminum nitride because you have an aluminum atom bonded to a nitrogen atom. Since this is a binary compound there is a positive and a negative ion. The positive ion is aluminum, because it is a metal,so the nitrogen is the negative ion. Now we write aluminum as the name of the metal, and nitr as the prefix of the second word (because nitrogen's stem is nitr). Lastly, we attach the suffix ide behind the nitr to get the name aluminum nitride.


K2S is potassium sulfide

K2S is potassium sulfide because you have a potssium atom bonded to a sulfur atom. Since this is a binary compound there is a positive and a negative ion. The positive ion is potassium, because it is a metal, so the sulfur is the negative ion. Now we write potassium as the name of the metal, and sulf as the prefix of the second word (because sulfur's stem is sulf). Lastly, we attach the suffix ide behind the sulf to get the name potassium sulfide.


NaCl is sodium chloride

NaCl is sodium chloride because you have a sodium atom bonded to a chlorine atom. Since this is a binary compound there is a positive and a negative ion. The positive ion is sodium, because it is a metal, so the chlorine is the negative ion. Now we write sodium as the name of the metal, and chlor as the prefix of the second word (because chlorine's stem is chlor). Lastly, we attach the suffix ide behind the chlor to get the name sodium chloride.


Remember that the positively charged ion is the name of the metal, while the negatively charged ion consists of its stem plus a suffix (so far we have only used IDE). So far we have seen that in the name of a chemical compound, the first element usually is positive, and is the first part of the name. The second element in the compound's name is usually negative.

NaCl

Na is the metal, and has a positive charge of 1

Cl is the second part of the compound, a nonmetal, and has a charge of -1

We now find that the ammonium radical, NH4+, is considered as a simple positive ion, and even though it is not a metal, it would go at the front of a compound name. Here are some examples:




NH4Cl is ammonium chloride

NH4Cl is ammonium chloride because you have an ammonium radical bonded to a chlorine atom. Since this is considered a binary compound there is a positive and a negative ion. The positive ion is ammonium even though it is not a metal. That makes the the chlorine the negative ion. Now we write ammonium as the name of the metal, and chlor as the prefix of the second word (because chlorine's stem is chlor). Lastly, we attach the suffix ide behind the chlor to get the compound's name, ammonium chloride.


(NH4)2S is ammonium sulfide

(NH4)2S is ammonium sulfide because you have an ammonium radical bonded to a sulfur atom. Since this is a binary compound there is a positive and a negative ion. The positive ion is ammonium even though it is not a metal. That makes the sulfur the negative ion. Now we write ammonium as the name of the metal, and sulf as the prefix of the second word (because sulfur's stem is sulf). Lastly, we attach the suffix ide behind the sulf to get the compound's name, ammonium sulfide.



There are also two negative groups which are considered as special cases: the hydroxide radical, OH-, and the cyanide radical, CN-, are considered as simple negative ions. This means that they are added at the end of the compound name.




KCN is potassium cyanide

KCN is potassium cyanide because you have a potassium atom bonded to a cyanide atom. Since this is a binary compound, there is a positive and a negative ion. The positive ion is potassium because it has a positive charge. CN-, the cyanide ion, is considered the negative ion. Now we write potassium as the name of the metal, and cyanide is the negative ion.
Mg(OH)2 is magnesium hydroxide
NH4CN is ammonium cyanide


Some metallic ions can have two valence states, the one with the lower valence has the ending OUS while the one with the higher valence has the ending IC. Under the new international system, the valence is designated by a Roman numeral.




Fe+2 is the ferrous ion or iron (II) ion
Fe+3 is the ferric ion or iron (III) ion

Cu+1 is the cuprous ion or copper (I) ion
Cu+2 is the cupric ion or copper (II) ion

Pb+2 is the plumbous ion or lead (II) ion
Pb+4 is the plumbic ion or lead (IV) ion

Sn+2 is the stannous ion or tin (II) ion
Sn+2 is the stannic ion or tin (IV) ion

The rules given above apply to compounds of these elements in the same manner.

CuS is cupric sulfide or copper (II) sulfide
FeCl2 is ferrous chloride or iron (II) chloride



When naming binary covalent compounds formed between two nonmetals, another system of nomenclature is preferred in which the numbers of each atom in a molecule are specified by a Greek prefix.

Number

Prefix

2

di

3

tri

4

tetra

5

penta

6

hexa

7

hepta

8

octa

9

nona

10

deca



NO2 is nitrogen dioxide

NO2 is nitrogen dioxide because you have a nitrogen atom bonded to two oxygen atoms. Since this is a binary compound of two nonmetals, we use the new way of naming we just learned. We keep nitrogen as the first name, and attach the prefix di before the oxygen because there are two atoms of oxygen. We then add the ox stem from oxygen after the di prefix. We attach the ide suffic after ox, and we have the finished product, nitrogen dioxide.

N2O4 is dinitrogen tetroxide
PCl3 is phosphorus trichloride

In some cases the prefix mono is used to avoid ambiguity.

Examples :

CO is carbon monoxide
CO2 is carbon dioxide


Naming Binary Compounds | Naming of Acids | Naming of Acids with Oxygen | Top of Page | Questions | Glossary



Naming of Acids

For binary compounds with hydrogen as the positive ion, place the term HYDRO at the front of the stem of the negative ion, the letters IC at the end of the stem, and add the word acid.

Examples :

HBr is hydrobromic acid
H2S is hydrosulfuric acid
HF is hydrofluoric acid
H2Te is hydrotelluric acid
HCN is hydrocyanic acid


Naming Binary Compounds | Naming of Acids | Naming of Acids with Oxygen | Top of Page | Questions | Glossary


Naming of Acids with Oxygen

These acids have hydrogen as the positive ion and a radical containing oxygen as the negative ion. If the radical ends in ATE , take off the ate, put on IC and add the word acid.

Examples :

HNO3 is nitric acid
HClO3 is chloric acid
H2CrO4 is chromic acid
H2SO4
is sulfuric acid
H3PO4 is phosphoric acid

If the radical ends in ITE, take off the ite, put on OUS and add the word acid.

Examples :

HNO2 is nitrous acid
H2SO3 is sulfurous acid
HClO is hypochlorous acid


Naming Binary Compounds | Naming of Acids | Naming of Acids with Oxygen | Top of Page | Questions | Glossary


 

Chemical Composition


Molecular Weight, Percent Composition, Empirical Formula

The molecular weight of a substance is the sum of the atomic weight of the atoms in a molecule. The atomic weight is the average atomic mass for a naturally occurring element. This means that molecular weight is the average mass of a molecule of a substance. Molecular weight is expressed in atomic mass units. For example, we might want to find the molecular weight of a molecule of water. We have 2 atoms of H, with each hydrogen atom weighing 1 amu. We multiply 2 H atoms by 1 amu a piece to get 2 amu. We add the 16 amu from one O atom to the 2 amu from the oxygen to get a total of 18 amu for one molecule of water.

H2O = 2 atoms of hydrogen and 1 molecule of oxygen

2 H * 1 amu = 2 amu

1 O * 16 amu = 16 amu

2 amu + 16 amu = 18 amu = molecular weight of water


The formula weight of a substance is the sum of the atomic weights of all atoms in a formula unit of the compound. Formula weight doesn't depend on whether or not the substance is a molecule.For example, sodium chloride, which is NaCl, has a formula weight of 58.44 amu. This results from having 22.99 amu from Na and 35.45 amu from Cl. You would use the formula weight for substances which are not molecules, such as ionic compounds.

Gram Formula Weight Examples:

Find the gram formula weight of H2SO4

  1. 2H = 2 x 1 = 2

    1S = 1 x 32 = 32

    4O = 4 x 16 = 64

    98g/mole

  2. Find the gram formula weight of Na2CO3 . 10 H2O

2Na = 2 x 23 = 46

1C = 1 x 12 =12

3O = 3 x 16 = 48

10H2 = 10 x 18 = 180

286g/mole


Sometimes we want to find out what the formula of a compound would be. To figure this out, we analyze the compound into amounts of the elements for a given amount of the compound. This is expressed as the percent composition which is the mass percentages of each different element in a compound. We must know the molecular weight of the compound in order to determine the molecular formula.

Say we have an element X in a compound. This element X is just part of the whole compound. We define the mass percentage of X as the parts of X per hundred parts of the total, by mass. That is:

Mass % X = (mass of X in the whole)/(mass of the whole) * 100%

Percent Composition Example:

Calculate the percent composition of Mg(NO3)2

1Mg = 1 x 24 = 24

2N = 2 x 14 = 28

6O = 6 x 16 = 96

148g/mole

%Mg = 24/148 x 100 = 16.2%

%N = 28/148 x 100 = 18.9%

%O = 96/148 x 100 = 64.0%

The percentage composition of a compound leads directly to its empirical formula. An empirical formula for a compound is the formula of a substance written with the lowest integer subscripts. For example, hydrogen peroxide has the molecular formula H2O2. The molecular formula tells us the precise number of atoms of different elements in the substance. The empirical number tells us ratio of numbers of atoms in the compound. The empirical formula of hydrogen peroxide is HO, while the molecular formula is H2O2. Compounds with different molecular formulas can have the same empirical formulas and such substances will have the same percentage composition. An example is acetylene, C2H2 and benzene, C6H6. In order to obtain the molecular formula of a substance, you need to know the percent composition and the molecular weight. The molecular weight allows us to choose the correct multiple of the empirical formula for the molecular formula.

Empirical Formula Example:

Determine the empirical formula for a compound which is 54.09% Ca, 43.18% O, and 2.73% H

Divide each percent by that element's atomic weight. To get the answers to whole numbers, divide through by the smallest one.

Ca = 54.09/40 = 1.352

1.352/1.352 = 1

O = 43.18/16 = 2.699

2.699/1.352 = 2

H = 2.73/1 = 2.73

2.73/1.352 = 2

CaO2H2 =

Ca(OH)2

Calcium Hydroxide


Molecular Weight, Percent Composition, Empirical Formula | Molecular formula from Empirical Formula | Top of Page | Questions | Glossary


Molecular formula from Empirical Formula

The molecular formula of a compound is a multiple of its empirical formula. The empirical formula is the simplest formula of a substance, written with the smallest integers. For example, the molecular formula of benzene C6H6is equivalent to the empirical formula, (CH)6. This means that the molecular weight is some multiple of the empirical formula weight. The empirical formula weight is obtained by summing the atomic weights from the empirical formula. For any kind of molecular compound, we can write:

Molecular weight = n * empirical formula weight


where n is the number of empirical formula units in a compound. We can get the molecular formula by multiplying the subscripts of the empirical formula by whatever n is. We can calculate this from the equation:

n = (molecular weight)/(empirical formula weight)

Once we determine the empirical formula of a compound, we can calculate is empirical formula weight. If we have an experimental determination of its molecular weight, we can calculate n and then its molecular formula.

Molecular Formula Example:

A hydrocarbon is 84.25% carbon and 15.75% hydrogen and has a molecular weight of 114. What is its molecular formula?

C 84.25/12 = 7.021

7.021/7.021 = 1 x 4 = 4

H 15.75/1 = 15.75

15.75/7.021 = 2.25 x 4 = 9

4 C = 48

9 H = 9

57

114 / 57 = 2

2(C4H9) = C8H18

Octane


Molecular Weight, Percent Composition, Empirical Formula | Molecular formula from Empirical Formula | Top of Page | Questions | Glossary