Chemical Nomenclature for Inorganic Compounds

Instructor: Julie Zundel

Julie has taught high school Zoology, Biology, Physical Science and Chem Tech. She has a Bachelor of Science in Biology and a Master of Education.

Naming inorganic compounds can seem like a monumental task, but if you learn some basic rules it isn't so difficult. This lesson will go over naming binary molecular compounds, ionic compounds, oxyanions and acids.

Chemical Nomenclature

Your name tells the world a lot about you. For example, your last name lets everyone know who is in your family. The same holds true for inorganic chemistry, or the branch of chemistry that doesn't focus on carbon-hydrogen bonded compounds. Compounds, by the way, are just molecules that have at least two elements that are different. Learning inorganic chemistry nomenclature, or how to name inorganic compounds, will help you understand chemistry; so let's get started!

Binary Molecular Compounds

When elements bond, or attach, together they can do so in a few ways. Binary molecular compounds are made of two non-metal elements that have bonded together in a covalent bond, which is where elements share electrons. Binary means two, so you can see how the name originated.

Covalently bonded molecules share electrons as is depicted by the red and green dots in this image

Let's use the example NO_2 and go through the rules used to name binary molecular compounds.

1. Use the periodic table to determine what N and O stand for: nitrogen and oxygen.


2. Determine which element will go first in the name, which you can figure out by determining which element is the least electronegative. What? Electronegative means that an element wants the other element's electrons (greedy little suckers, I know!). The element that DOESN'T want the other element's electrons goes first in the name. So, how do you know which is which? Check out this table that lists elements from least to most electronegative.

Some elements from LEAST to MOST electronegative

So, based on this table, nitrogen will go before oxygen.

3. The element that goes second will get its ending changed to 'ide'. So, oxygen becomes oxide.

4. Add prefixes depending upon how many of each element you have. Take a look at this prefix table.

Number of Element Prefix
1 Mono
2 Di
3 Tri
4 Tetra
5 Penta
6 Hexa
7 Hepta
8 Octa

Based on the table, you may think that NO_2 would be mononitrogen dioxide since there's only one nitrogen (mono), but there's two oxygens (di). Well, there's another part to the rule. You don't put mono before the first element in the name, even if there is just one. So NO_2 is actually nitrogen dioxide.

Ionic Compounds

Ionic compounds have a different set of naming rules than binary molecular compounds. Ionic compounds get their name because the elements stick together in ionic bonds, or when one element takes the electrons from another element (there's no sharing here!). Ionic compounds are usually the result of an ionic bond between a metal and a non-metal.

Before we go through the rules for naming ionic compounds, there are a couple more vocabulary words you need to familiarize yourself with, starting with cation - and no, there isn't a cat element. Cations are typically the metal that gets its electrons taken away so it has a positive charge (electrons are negative).

Anions are usually the non-metals that take the electrons, so they have a negative charge. The charges of cations and anions are often written as superscripts next to the element's symbol. (For the purposes of this lesson, if you see a ^ symbol before a number in a compound, then you know that's a superscript, and if you see a _ before a number in a compound then you know it's a subscript.) The superscripts, however, are not part of the ionic compound's name. Let's take a look at the ionic compound NaCl to practice.

1. Figure out which is the cation and which is the anion. You can use the periodic table to figure out which element is the metal and which is the non-metal (remember the metal is the cation and non-metal is the anion). The cation goes first in the name, followed by the anion.

2. Change the anion's ending to 'ide'.

So NaCl is sodium chloride.

Transition metals , or the group of elements in the middle of the periodic table, have roman numerals in their name. This is because transition metals don't necessarily give up the same number of electrons every time. For example, copper can give up one, two, three or four electrons. The roman numerals let you know how many electrons the transition metal gave up. So CuO is copper (II) oxide, which means copper (II) gave up two electrons, whereas CuCl is copper (I) chloride, where copper only gave up one electron. It's a little confusing, so for the purposes of this lesson just make sure you know that transition metals have roman numerals to show how many electrons they gave up.


Oxyanions are a type of anion that contains oxygen. I guess you can see how they get their name: OXY ANION! There are tons of oxyanions, so memorizing all of them would take forever. Luckily, there are some rules to help you here, too. Yay!

Most oxyanions have the ending 'ate'. In fact the oxyanions that are most commonly found in nature all end in 'ate'. You'll probably have to memorize the 'ate' ions. Take a look at the table for a handful of 'ate' oxyanions that you might encounter. If you know the 'ate' you can figure out the rest.

Oxyanion Name
CO_3 ^-2 Carbonate
NO_3^-1 Nitrate
PO_4^-3 Phosphate
SO_4^-2 Sulfate

You use the ending 'ite' when the oxyanion has ONE less oxygen but the same charge as the 'ate' oxyanion. For example, the oxyanion SO_3^-2 is sulfite (note one less oxygen than sulfate).

If you have two fewer oxygen atoms than the 'ate,' then you write 'hypo' and then the suffix 'ite'. For example, SO_2^-2 is hyposulfite. Hypo means 'under' in Latin, so it is referring to having fewer oxygen atoms than the 'ate'. Finally one more oxygen than the 'ate' gets the prefix 'per' and the suffix 'ate'. So SO_5^-2 is persulfate.

Now that you know the oxyanion rules, you just follow the same rules you saw for ionic compounds. Let's name Na_2 SO_4.

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