A binary compound is one made of two different elements. There can be
one of each element such as in CO or NO. There can also be several of each
element such as BF
This lesson shows you how to name binary compounds from the formula when two nonmetals are involved. The four formulas above are all examples of this type. Important point to remember: NO metals (which act as the cation) are involved. That means one of the nonmetals will be acting in the positive role while the other is negative.
In fact, you do not even need to know the charges, since the formula comes right from the element names and their prefixes. Be aware that heavy use of Greek number prefixes are used in this lesson.Here are the first ten:
one mono- six hexa-
two di- seven hepta-
three tri- eight octa-
four tetra- nine nona-
five penta- ten deca-
Example #1 - write the name for N2O.
Example #2 - write the name for NO2.
Step #1 - part of the first name is the unchanged name of the first element in the formula. In the examples above, it would be nitrogen.
If the subscript of the first element is 2 or more, you add a prefix to the name. In the first example above, you would write dinitrogen. If the subscript is one as in the second example above, you DO NOT use a prefix. You simply write the name, in this example it would be nitrogen.
Step #2 - the anion is named in the usual manner of stem plus "ide." In addition, a prefix is added. In the first example, the prefix is "mono-" since there is one oxygen. In the second example, use "di-" because of two oxygens.
The correct names of the two examples are dinitrogen monoxide and nitrogen dioxide.
Note that "monoxide" is written rather than "monooxide." It sounds better when spoken out loud.
Example #3 - write the name for IF7.
Step #1 - the first element is iodine and there is only one. This part of the name will be "iodine", NOT "monoiodine."
Step #2 - the second element is fluorine, so "fluoride" is used. Since there are seven, the prefix "hepta" is used.
The name of this compound is iodine heptafluoride.
Example #4 - write the name for N2O5.
Step #1 - the first element is nitrogen and there are two. This part of the name will be "dinitrogen."
Step #2 - the second element is oxygen, so "oxide" is used. Since there are five, the prefix "penta" is used.
The name of this compound is "dinitrogen pentaoxide." Many write is as "dinitrogen pentoxide." The ChemTeam believes that both are considered correct, but the second is to be prefered.
Example #5 - write the name for XeF2.
The first part of the name comes from the first element's name: xenon. Since there is only one atom present, no prefix is used.
The second part of the name comes from the root of the second symbol plus 'ide' as well as the prefix "di-,"therefore di + fluor + ide = difluoride.
This compound is named xenon difluoride.
Example #6 - write the name for N2O4.
The first part of the name comes from the first element's name: nitrogen. Since there are two atoms, the prefix "di-" is used giving dinitrogen.
The second part of the name comes from the root of the second symbol plus 'ide' as well as the prefix "tetra-,"therefore tetr + ox + ide = tetroxide.
This compound is named dinitrogen tetroxide. Notice the dropping of the "a" in tetra.
Just a reminder: this system of naming does not really have an offically accepted name, but is often called the Greek system (or method). It involves use of Greek prefixes when naming binary compounds of two nonmetals.
Sometimes you will see the Stock system applied to these types of compounds. Here is what the IUPAC currently says about that practice: "The Stock notation can be applied to both cations and anions, but preferably should not be applied to compounds between nonmetals."
Practice Problems
Write the correct name for:
1) As4O10
2) BrO3
3) BN
4) N2O3
5) NI3
6) SF6
7) XeF4
8) PCl3
9) CO
10) PCl5
Write the correct name for:
11) P2O5
12) S2Cl2
13) ICl2
14) SO2
15) P4O10
16) UF6
17) OF2
18) ClO2
19) SiO2
20) BF3
Write the correct name for:
21) N2S5
22) CO2
23) SO3
24) XeF6
25) KrF2
26) BrF5
27) SCl4
28) PCl3
29) XeO3
30) OsO4