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Parlez vous la chimie?   Do you speak chemistry?

Instead of teaching a set of nomenclature rules, which is the normal approach, I'd like to approach your learning of chemistry nomenclature in a way similar to learning a foreign language.

The picture here is of the Louvre Museum in Paris. If you were to move to Paris, you would begin learning the language little by little by listening. In other words you could begin to learn a few words that gives you some idea of what is being said. For example, if you hear "we", you learn that is the French word "Oui" meaning yes. Even if you didn't understand anything else, you would at least know that someone was agreeing with someone else.

In chemistry you don't even need a whole word, but just a syllable to gain some valuable information. For example, you were walking by these two guys and you heard part of the conversation:

"When you mix ___ium  ___ide with the ___ide ion the solution turns yellow."

The ending of "ium" tells you that they are probably talking about a metal (like sodium, calcium, potassium, etc.). There are only three exceptions: "helium" and the heavy isotopes of hydrogen: deuterium & tritium.

The syllable of "ide" tells us that this is a compound made up of only two elements. For example, "carbon dioxide." Notice that is made up of just two elements, carbon and oxygen.

The exception is if you hear "___ide ion" That means it's a negative ion of some element. For example, chlorine that has gained an electron to become an ion is called a chloride ion and not a chlorine ion. Positive ions don't use the "ide" ending.

NaCl, CaO, CaCl2, N2O, CO2, KBr, P5O10

Sodium chloride, calcium oxide, calcium chloride, dinitrogen oxide, carbon dioxide, potassium bromide, and pentaphosphorus decaoxide.

Even if you don't know the names of the compounds on the left, you now know they all end in "ide" because each are a combination of two elements. There can be more than two atoms, but only two elements. The only two exceptions I can think of is "hydroxide" and "cyanide" compounds, such as sodium hydroxide (NaOH) and sodium cyanide (NaCN) . Notice that these have 3 elements. Again, "ide" usually means there's just two elements combined.

I'll show you how valuable this little syllable is.

Let's say you and a friend overhear a conversation. Later the FBI interview both of you saying the people you heard were suspected terrorists. The FBI believe they are shipping a dangerous chemical.

You did hear some chemical names being mentioned. Your friend says he heard "sodium" followed by a word that sounded like "chlorine". You also heard "sodium" but don't remember "chlorine" being said, but you are absolutely sure you heard "ide" at the end of the second word's name.

If the word "sodium" is heard by itself, then they are most likely talking about sodium metal. This is very dangerous. In contact with water, it will explode.

The word "chlorine" by itself is refering to toxic chlorine gas. In World War I, chlorine gas was released to kill enemy soldiers.

So the words, "sodium, chlorine" could easily mean that the terrorists have both sodium metal and chlorine gas. These are potent and deadly chemicals.

However, since you heard "ide", this changes the whole meaning. Instead of "sodium, chlorine," the words must have been "sodium chloride," which is table salt. Remember the "ide" means this is a compound made from two elements, in this case sodium and chlorine. Individually sodium and chlorine are very reactive and dangerous; however, once they combine, they are safe and good on french fries. So cancel the terrorist alert.

If you have high blood pressure, the doctor is apt to tell you to reduce your intake of sodium chloride (table salt) and instead use potassium chloride.

One of these bottles contain just what you need to prevent a heart attack; unfortunately, instead of the compound being written out as "potassium chloride," it is written as a formula. Both of these elements have potassium and chlorine atoms. Again, "ide" is the clue that the correct bottle is the left one because it has just two elements. The right bottle has 3 elements. It's name is potassium chlorate. If you were to cook with this kind of salt, your food would likely explode. So you see, there's a big difference between ending with "ide" or with "ate".

Learning a language means paying attention to patterns. Let's say below is what you see written:

NaCl, KBr, CaF2

You recognize the elements as sodium, chlorine, potassium, bromine, calcium, and fluorine. Now you hear someone read the compounds outloud as, "sodium chloride, potassium bromide, calcium fluoride." You see a pattern. The first element is read as is, the second element's name is shortened and the suffix "ide" is added.

Here's a list of the element names: lithium, chlorine, magnesium, oxygen, sodium, fluorine, calcium, and chlorine. Try naming the compounds to the left.

To see the answer, roll cursor over the image.

When learning a language, you often encounter things that seem inconsistent. Notice the discrepancy between how these compounds indicate the number of atoms. Some compounds do and some don't. Can you see a pattern here? (roll cursor over image for answer)

All elements above the yellow stair-step line are non-metals. Whenever any two combine, we need to indicate how many of each are present. The reason for this is that there's often several possibilities. For example, nitrogen and oxygen combine with each other in various numbers, so we can't just say "nitrogen oxide" because that wouldn't identify the various compounds.
NO, N2O, NO2, N2O3

Notice that these four compounds of nitrogen are called: nitrogen oxide, dinitrogen oxide, nitrogen dioxide, and dinitrogen trioxide.

At this point, you would conclude that "di" means two and "tri" means three.

When you learn a language, one of the first things you learn is how to count. In chemistry, we use Greek to count.

1= mono (mono isn't used much. 1 is understood)
2 = di
3 = tri
4 = tetra
5 = penta
6 = hexa
7 = hepta
8 = octa
9 = nona
10 = deca

These seven non-metals usually form toxic compounds. So if you ever hear these spoken or see them written, take notice.

Most end with the syllable "ide" and they use the Greek prefix to indicate the number of atoms. For example, the last one says, "phosphorus trichloride". Ammonia could be called "nitrogen trihydride" but the ammonia is so well known, that no one says the full name.

dichlorine heptaoxide (heptoxide)

dinitrogen tetraoxide (tetroxide)

phosphorus triiodide

We now have some nomenclature rules about naming compounds that are made of two different non-metals.

1. The first element is written as. If more than one atom of that element, use the Greek prefix for that number.

2. The name of second element is shortened and the suffix "ide" is added. If more than one atom of the second element, then use the Greek prefix for that number.

Here I'm talking chemistry to a couple of textbooks authors. If I hear Greek_something_Greek_something_ide, I know they are talking about a non-metal compound of two elements even if I didn't catch the element names.

When reading chemistry, you see and hear Greek words for counting the elements in non-metal compounds, but when discussing compounds made from a metal and a non-metal, you see Roman Numerals but hear Arabic numerals. It almost makes you want to use your sword on someone.


Written: iron(II) chloride
Spoken: iron two chloride

Written: cobalt(III) oxide
Spoken: cobalt three oxide

Notice that the Roman numeral (III) is spoken as if it were the Arabic numeral "3". We say "three" not "I, I, I", which would make people think you stutter.

Spoken: "chromium four oxide"

Written out: Chromium (IV) oxide

Another puzzler: You see the formula CrO2, but are puzzled because someone calls it "chromium four oxide". To you it looks like there's two oxygens not four. The reason for this is that the "four" is referring to the charge on the chromium not the number of oxygen atoms.

Here's a diagram of what chromium and oxygen atoms look like individually. They start off neutral because the electrons (e-) they have match the number of protons (p+) they have.
Since each oxygen has a stronger pull on electrons than does chromium, each will pull off two electrons from the chromium. Chromium has four outer electrons and these get grabbed by the two oxygen atoms. Now chromium has 4 more protons than it does electrons, so it is now 4+ charge. The oxygens have gained 2 electrons each, so they are now 2- charge. Because these elements now have opposite charges, they stick together to make chromium (IV) oxide.


Copper(II) chloride > CuCl2

Calcium chloride > CaCl2

Sodium chloride > NaCl

Two more puzzlers:
1) Sometimes you hear Roman numerals used and sometimes not.
2) Why did they write two chlorines for calcium chloride (CaCl2), but only one chlorine for sodium chloride (NaCl)?

No need to say more than what's needed:

You wouldn't try to use hand signals to tell your friends here that there's a Shark-with-a-lot-of-sharp-teeth right behind them. Giving them the signal for "shark" is all you need.

Chemists are like scuba divers. There's no need to say more than what's necessary. When a group shares a certain amount of knowledge, communication can be shortened because of this shared knowledge.

Chloride ion = Cl-

Sodium ion = Na+ and attracts one Cl-

Calcium ion = Ca2+ and attracts two Cl-

NaCl (no need to say one chlorine because sodium can only attract one)

CaCl2 (no need to say two chlorines, in other words, you would not say calcium dichloride because it's unnecesary when you know that calcium has 2+ charge. That 2+ charge would always attract two chloride ions which have a negative one charge each).

Chemistry nomenclature can be puzzling if we don't have the knowledge that chemists share. What they know is the charge on elements.

Chlorine is a negative one charge, so it's attracted to the positive metal ions like sodium and calcium. When a sodium atom becomes a charged ion, it always becomes 1+ charge. Calcium always becomes a 2+ (two plus) charge.

Copper ion = Cu+ or Cu2+

copper (I) chloride means Cu+ so attracts one Cl- (CuCl)

copper (II) chloride means Cu+ so attracts two Cl- (CuCl2)

Unlike copper and sodium, a copper ion can be either 1+ charge or a 2+ charge. So simply saying copper chloride doesn't tell you how many chloride ions are attached to the copper. However, if you indicate the charge on the copper, then others can figure out how many chlorine atoms are connected.
This is the Periodic Table where the middle is left out so we can focus on both ends. Notice that elements in the first column will achieve a +1 charge (also written 1+) if they lose their outer single electron. Sodium (Na) mentioned above is in this column. The second column are metals that acquire a plus two charge when they lose their two outer electrons. Calcium mentioned above is in this column. Non-metals are on the right side and they become negatively charged as they take electrons away from the metals. Notice chlorine has a negative one charge.


Do not say magnesium dichloride
Saying magnesium chloride is enough

It's the knowledge of the charges that speeds up communication. For example, a person does not need to say "magnesium dichloride" because magnesium is in the plus 2 charge column, and since chlorine is a negative 1 charge, there will always be two chloride ions attached to a magnesium ion.

Here's the motto: "Don't tell me something I already know."

It's like saying "yellow bananas", "wet water", or "4 legged horse." Don't use these extra words that are already common knowledge.

On the other hand, don't leave out words that are needed.

The main ingredient of glass is silicon dioxide (SiO2). Sometimes aluminum oxide (Al2O3) is added to make the glass more resistant to chemicals.

Why didn't we say dialuminum trioxide for (Al2O3)? One reason is that we have a metal combined with a non-metal, so we don't use Greek prefixes to count the atoms.

How do we know aluminum oxide has two aluminum atoms and three oxygen atoms?

We refer to this Periodic Table that lists the charges that these elements can have. Aluminum is in the +3 column meaning it loses 3 electrons to become +3 charge. Oxygen is in the -2 column and can have a -2 charge. Having opposite charges, the two are attracted to each other. However, after they are together, they still have an overall +1 charge.

That means as a pair, they will attract another negative oxygen atom.
(Al3+O2-)+  ← O2-
This resulting threesome now has a negative one charge (3+ & 4-=1-), so they will now attract a positive aluminum ion.
(O2-Al3+O2-)- ← Al3+
This results in a group that has a plus 2 charge
Being positive they now attract a O2-.
(Al3+O2-Al3+O2-)2+ ← O2-
Now all together there is no charge, so the compound attracts nothing else and we end with the final compound & formula.
which is Al2O3. Also, aluminum never has other charges, so we can depend on it having a +3 charge, so we don't write:
aluminum(III) oxide, we only write aluminum oxide.

A compound that comes together just like aluminum oxide is iron(III) oxide (rust). Notice for the iron compound, I wrote "(III)". That's because iron can have either a plus 2 charge or a plus 3 charge. So I had to specify which one. It's formula is like aluminum oxide (Al2O3); it's Fe2O3. Two iron atoms with plus 3 charge each balances with three oxygen atoms with negative 2 charge each just like the aluminum and oxygen atoms did.

Learning the language of chemistry takes time. Like any language, the more you are learn the faster it is to learn more. Also, understanding the logic behind the naming rules helps. Even though there is quite a bit of memorization in nomenclature, remember, it's not just names that are important, it's the chemical behind the name.

The payoff with learning how to speak chemistry is that it lets you communicate with so many others around the world that also have learned the language of chemistry.


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Since March 13, 2008