Naming Binary Compounds: Ionic and Covalent Compounds

Many students struggle with naming compounds in their introductory chemistry course.  Although there is a hefty amount of memorizing involved, if you are able to identify where your element lies on the periodic table, you are well on your way to successfully naming these compounds.

Step-by-step instruction for naming compounds.

First identify whether you compound is ionic or covalent.  Ionic compounds contain a metal and a non-metal.  Covalent compounds contain two non-metals.  How do you determine whether an element is a metal?
Simply refer to your periodic table.  Metals are listed to the left of the thick stair-case line on the right hand side of the periodic table.  Non-metals are grouped to the right of that line.  Another feature of the periodic table indicates that metallic behavior increases as you travel down a group and decreases as you go from left to right across a row.  This will be important when we get to naming covalent binary compounds.

Binary Compounds
All binary compounds are named with the more metallic element listed first and the more electronegative element listed second.  Replace the ending of the electronegative element with -ide and you are pretty much on your way to naming your compound.

Ionic Binary Compounds – Metal from Group 1A, 2A, 3A, or 4A (except Sn or Pb) and including Zn, Ag, and Cd

If your compound is an ionic binary compound, and the metal is of group 1A, 2A, 3A, or 4A (except Sn or Pb), write the metal using its element name (usually ending in -ium).  Then write the nonmetal element name second replacing the last three letters with -ide.

Ionic Binary Compounds – Transition Metals (except Zn, Ag, and Cd) and including Sn and Pb

Metals in the transition group often have multiple oxidation numbers. If your metal falls in the transition groups (make sure to include Sn and Pb), then use Roman numerals to identify the oxidation number.  The Roman numeral follows the first element’s name.  Then write your non-metal element second with an –ide ending.

Covalent Binary Compounds

Covalent binary compounds are composed of two nonmetals.  Identify the location of each element on the periodic table. When writing the compound, list the more metallic element first.  (The only exception is when a halogen is pared with oxygen, write the halogen first).  This means that in a row, the lower number is more metallic and in a group, the higher number is more metallic.  Use Greek numerical prefixes (i.e. mono-. di-. tri- to indicate the number of atoms of each element.  If there is only 1 atom in the first element, you can drop the word mono-.  The second word ends with -ide and always has a prefix.

For more information visit Science Matters Wiki as well as the forum for some practice problems.

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