Chemical nomenclature is the term given to the naming of compounds. Chemists use specific rules and "conventions" to name different compounds. This section is designed to help you review some of those rules and conventions.

There are five sections to this reading:

1. Forming ionic compounds
2. Naming ionic compounds
3. Naming molecular compounds
4. Naming acids
5. Naming organic compounds

Oxidation

1. An atom of a pure element has an oxidation number of zero.
2. For single atoms in an ion, their oxidation number is equal to their charge.
3. Fluorine is always -1 in compounds.
4. Cl, Br, and I are alway -1 in compounds except when the are combined with O or F.
5. H is normally +1 and O is normally -2.
6. The oxidation number of a compound is equal to the sum of the oxidation numbers for each atom in the compound.

Forming Ionic Compounds

Knowing the oxidation number of a compound is very important when discussing ionic compounds. Ionic compounds are combinations of positive and negative ions. They are generally formed when nonmetals and metals bond. To determine which substance is formed, we must use the charges of the ions involved. To make a neutral molecule, the positive charge of the cation (positively-charged ion) must equal the negative charge of the anion (negatively-charged ion). In order to create a neutral charged molecule, you must combine the atoms in certain proportions. Scientists use subscripts to identify how many of each atom makes up the molecule. For example, when combining magnesium and nitrogen we know that the magnesium ion has a "+2" charge and the nitrogen ion has a "-3" charge. To cancel these charges, we must have three magnesium atoms for every two nitrogen atoms:

Knowledge of the charges of ions is crucial to knowing the formulas of the compounds formed.

• alkalis (1st column elements) form "+1" ions such as Na⁺ and Li⁺
• alkaline earth metals (2nd column elements) form "²⁺" ions such as Mg²⁺ and Ba²⁺
• halogens (7th column elements) form "-1" ions such as Cl^1- and I^1-

Naming Ionic Compounds

Positive Ions

1. Monatomic cations (a single atom with a non-negative charge) take the name of the element plus the word "ion"
   
   Examples:
   
   • Na⁺ = sodium ion
   • Zn = zinc ion
   
   
2. If an element can form more than one (1) positive ion, the charge is indicated by Roman numeral in parentheses followed by the word "ion"
   
   Examples:
   • Fe²⁺ = iron(II) ion
   • Fe³⁺ = iron (III) ion

1. Monatomic anions (a single atom with a negative charge) change their ending to "-ide"
   
   Examples:
   
   • O^2- = oxide
   • Cl^- = chloride
   
   
2. Oxyanions (negatively charged polyatomic ions which contain O) end in "-ate". However, if there is more than one oxyanion for a specific element then the endings are:
   
   

   Two less oxygen than the most common starts with "hypo-" and ends with "-ite"	One less oxygen than the most common ends with "-ite"	THE MOST COMMON OXYANION ENDS WITH "-ATE"	One more oxygen than the most common starts with "per-" and ends with "-ate"<
   ClO- = hypochlorite	ClO2- = chlorite NO2- = nitrite SO32- = sulfite	Most common oxyanions with four oxygens SO42- = sulfate PO43- = phosphate CrO42- = chromate Most common oxyanions with three oxygens NO3- = nitrate ClO3- = chlorate CO32- = carbonate	ClO4- = perchlorate

   
   
3. Polyatomic anions (a negatively charged ion containing more than one type of element) often add a hydrogen atom; in this case, the anion's name either adds "hydrogen-" or "bi-" to the beginning
   
   Example:
   CO₃^2- becomes HCO₃^-
   "Carbonate" becomes either "Hydrogen Carbonate" or "Bicarbonate"
   
   
4. When combining cations and anions into an ionic compound, you always put the cation name first and then the anion name (the molecules are also written in that order as well.)
   
   Examples:
   
   • Na⁺ + Cl^- --> NaCl
     sodium + chloride --> sodium chloride
     
   • Cu²⁺ + SO₄^2- -->CuSO₄
     copper(II) + sulfate --> copper(II) sulfate
     
   • Al³⁺ + NO₃^- --> Al(NO₃)₃
     aluminum + nitrate --> aluminum nitrate

Arrangement of Atoms

In naming ions, it is important to consider "isomers." Isomers are compounds with the same molecular formula, but different arrangments of atoms. Thus, it is important to include some signal within the name of the ion that identifies which arrangement you are talking about. There are three main types of classification, geometric, optical and structural isomers.

1. Geometric isomers refers to which side of the ion atoms lie. The prefixes used to distinguish geometric isomers are cismeaning substituents lie on the same side of the ion and transmeaning they lie on opposite sides. Below is a diagram to help you remember.
2. Optical isomers differ in the arrangement of four groups around a chiral carbon. These two isomers are differentiated as L and D.
3. Structural isomers differentiate between placement of two chlorine atoms around a hexagonal carbon ring. These three isomers are identified as o,m,and p. Once again we have given you a few clues to help your memory.

A pop-up nomenclature calculator is available for help when naming compounds and for practice problems.

Naming Binary Molecular Compounds

1. The more positive atom is written first (the atom which is the furthest to the left and to the bottom of the periodic table)
2. The more negative second atom has an "-ide" ending.
3. Each prefix indicates the number of each atom present in the compound.
   

Examples:
CO₂ = carbon dioxide
P₄S₁₀ = tetraphosphorus decasulfide

Naming Inorganic Acids

1. Binary acids (H plus a nonmetal element) are acids which dissociate into hydrogen atoms and anions in water. Acids which only release one hydrogren atom are known as monoprotic. Those acids which release more than one hydrogen atom are called polyproticacids. When naming these binary acids, you merely add "hydro-" (denoting the presence of a hydrogen atom) to the beginning and "-ic acid" to the end of the anion name.
   
   Examples:
   HCl = hydrochloric acid HBr = hydrobromic acid
   
2. Ternary acids (also called oxyacids, are formed by hydrogen plus another element plus oxygen) are based on the name of the anion. In this case, the -ate,and -itesuffixes for the anion are replaced with -icand-ousrespectively. The new anion name is then followed by the word "acid." The chart below depicts the changes in nomenclature.
   
   

Example:
ClO₄ to HClO₄ => perchlorate to perchloric acid ClO to HClO => hypochlorite to hypochlorous acid

Naming organic compounds

1. Single bonds (alkane): suffix is "ane", formula C_nH_2n+2
2. Double bonds (alkene): suffix is "ene", formula C_nH_2n
3. Triple bonds (alkyne): suffix is "yne", formula C_nH_2n-2
4. Cyclic compounds: use prefix "cyclo"

So, for example, an organic compound with the formula "C₆H₁₄" would be recognized as an alkane with six carbons, so its name is "hexane".

Examples:
N₂O₄ = dinitrogen tetraoxide
S₂F₁₀ = disulfur decafluoride

Practice

2. Write the names of the following molecules:

1.	CaCO3			8.	Mg3(PO4)2
2.	SCl2			9.	Ba(NO2)2
3.	Li2CrO4			10.	Hg2Cl2
4.	NaSCN			11.	NaHCO3
5.	KClO3			12.	H2S
6.	Ca(C2H3O2)2			13.	H2SO3
7.	K2Cr2O7			14.	SO3

Nomenclature Atomic Structure Stoichiometry Acid Base Chemistry