CHEMISTRY - NAMING COMPOUNDS & BALANCING EQUATIONS #9

Naming Chemical Compounds

Chemical compounds are formed when elements are joined by chemical bonds.    These bonds are so strong that the compound behaves like a single substance. Compounds have their own properties that are unique from the elements they are made of. A compound is a type of molecule with more than one element. 

How Compounds are Named 

Chemists have a specific way of naming compounds. It is a standard method of naming compounds that is used by scientists around the world. The name is built from the elements and the construction of the molecule. 

Basic Naming Convention 

First we'll cover how to name molecules with two elements (binary compounds). The name of a compound with two elements has two words. 

To get the first word we use the name of the first element, or the element to the left of the formula. To get the second word we use the name of the second element and change the suffix to "ide" at the end of the word. 

Some examples of adding the "ide": 

O = oxygen = oxide
Cl = chlorine = chloride
Br = bromine = bromide
F = fluorine = fluoride 

Examples of binary compounds: 

NaCl - sodium chloride
MgS - magnesium sulfide
InP = indium phosphide 

What if there is more than one atom? 

In cases where there is more than one atom (for example there are two oxygen atoms in CO₂) you add a prefix to the start of the element based on the number of atoms. Here is a list of the prefixes used: 

# Atoms 1 2 3 4 5 6 7 8 9 10

Prefix mono- di- tri- tetra- penta- hexa- hepta- octa- nona- deca-

** note: the "mono" prefix is not used on the first element. For example CO = carbon monoxide. 

Examples: 

CO₂ = carbon dioxide
N₂O = dinitrogen monoxide
CCL₄ = carbon tetrachloride
S₃N₂ = trisulfer dinitride 

How is the order of the elements determined? 

When there are two elements in a compound, which element goes first in the name? 

If the compound is made of a metal element and a nonmetal element, then the metal element is first. If there are two nonmetal elements, then the first name is the element to the left side of the periodic table. 

Examples:

• In a compound that contains iron and fluoride, the metal (iron) would go first.
• In a compound that contains carbon and oxygen the element to the left on the periodic table (carbon) would go first.

More Complex Naming Rules 

See below for some of the more complex naming rules. 

Naming Metal-Nonmetal Compounds 

If one of the two compounds is a metal, then the naming convention changes a bit. Using the stock method, a roman numeral is used after the metal to indicate which ion is using the charge. 

Examples: 

Ag₂Cl₂ = silver (II) dichloride
FeF₃ = iron (III) fluoride 

Naming Polyatomic Compounds 

Polyatomic compounds use a different suffix. Most of them end in "-ate" or "-ite". There are a few exceptions that end in "-ide" including hydroxide, peroxide, and cyanide. 

Examples: 

Na₂SO₄ = sodium sulfate
Na₃PO₄ = sodium phosphate
Na₂SO₃ = sodium sulfite 

Naming Acids 

Hydro acids use the prefix "hydro-" and the suffix "-ic". 

HF = hydrofluoric acid
HCl - hydrochloric acid 

Oxoacids containing oxygen use the "-ous" or the "-ic" suffix. The "-ic" suffix is used for the acid that has more oxygen atoms. 

H₂SO₄ = sulfuric acid
HNO₂ = nitrous acid
HNO₃ = nitric acid