Naming Compounds
What are Binary Ionic Compounds?
Compounds made of only two elements made into ions. The formula may have many of each element, but there are only two types.
Example: NaCl
Example: NaCl
Important Rules!!!
Rule # 1 = On a stable atom or molecule, the number of electrons must be the same as the number of protons.
Rule #2 = On a stable atom or molecule, the valence layer has a stable number of electrons.
Naming Binary Ionic Compounds
Naming compounds follows rules that make it easier for scientists from around the world to know exactly what is the compound without needing to look at the formula. In this case, the name of a binary compound always starts by saying the name of the positive ion. Then, you use one of the modified names for the negative ion to complete the molecular name. See the table below.
Common Negative Ions of Non-Metals
How would you read KI ? --> The answer is: Potassium Iodide.
What if a compound is formed by Magnesium and Sulfur? The name will be... Magnesium Sulfide
What if a compound is formed by Magnesium and Sulfur? The name will be... Magnesium Sulfide
You know those small numbers we see to the right of each element? These are called subscripts. The subscripts indicate the ratio of each type of ion in the compound. If no subscript is shown, remember to assume the number is 1!
For example, the formula Ag2O means there are 2 atoms of Silver for every atom of Oxygen. The chemical formula for an ionic compound represents the smallest repeating part of the crystal lattice. This unit is called the formula unit for that compound. Take a look below to see some examples of chemical formulas of binary ionic compounds, and their meanings!
For example, the formula Ag2O means there are 2 atoms of Silver for every atom of Oxygen. The chemical formula for an ionic compound represents the smallest repeating part of the crystal lattice. This unit is called the formula unit for that compound. Take a look below to see some examples of chemical formulas of binary ionic compounds, and their meanings!
Writing Formulas of Ionic Compounds
Although an ionic compound is made up of ions, overall the compound is electrically neutral (this means it has no charge). So the positive charges on the metal ions must balance the negative charges on the non-metal ions. For example, in aluminum oxide, there are two aluminum ions, Al3+, and three oxide ions, O2-. What is the total charge?
Charge from Al3+ ions: There are 2 aluminum ions in the
formula, each with a charge of 3+. 2x (3+) = 6+
Charge from O- ions: There are 3 oxide ions in the formula, each with a charge of 2-. 3 x (2-)=6-
Total charge: (6+)+(6-) = 0
When writing the formula of a binary ionic compound, you first need to determine the charges on the ions.
Let's look at the table a few paragraphs above, again. That one lists the ions of non-metals. For metals that form only one type of ion, all you need to do to figure out the ion charge is to look at the periodic table, as shown in the figure below. (You can find the charges for non-metal ions on the periodic table, too.)
Once you know the charges, you can figure out the formula.
The periodic table usually lists the charges of ions commonly formed by the various elements.
Charge from Al3+ ions: There are 2 aluminum ions in the
formula, each with a charge of 3+. 2x (3+) = 6+
Charge from O- ions: There are 3 oxide ions in the formula, each with a charge of 2-. 3 x (2-)=6-
Total charge: (6+)+(6-) = 0
When writing the formula of a binary ionic compound, you first need to determine the charges on the ions.
Let's look at the table a few paragraphs above, again. That one lists the ions of non-metals. For metals that form only one type of ion, all you need to do to figure out the ion charge is to look at the periodic table, as shown in the figure below. (You can find the charges for non-metal ions on the periodic table, too.)
Once you know the charges, you can figure out the formula.
The periodic table usually lists the charges of ions commonly formed by the various elements.
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Multivalent Metals Form More Than One Ion
As you can see when you examine the periodic table, some metals form more than one type of ion. These metals are called multivalent metals. For example, copper can form ions with a 1+ or 2+ charge. To distinguish between the ions, a Roman numeral is written after the name of the metal.
For example, Cu+ is written as copper(I), pronounced "copper one." Cu2+ is written as copper(II), pronounced "copper two." On the periodic table, the ion charges for a given element are listed with the most common charge at the top and the least common charge at the bottom.
For example, Cu+ is written as copper(I), pronounced "copper one." Cu2+ is written as copper(II), pronounced "copper two." On the periodic table, the ion charges for a given element are listed with the most common charge at the top and the least common charge at the bottom.
Even though both are made of the same elements,
Copper(II) Oxide is black, while Copper(I) Oxide is red!
Copper(II) Oxide is black, while Copper(I) Oxide is red!
Naming and Writing Formulas for Ionic Compounds Containing Multivalent Metals
To write the chemical formula of a multivalent metal, follow the same process as for the binary ionic compounds you have been naming so far. The only difference is that you cannot tell the charge on the metal ion by looking at the periodic table because there is more than one choice. Instead, look at the Roman numeral in the name, which will tell you the charge.
The Roman numerals for charges 1+ through 7+ can be seen above. For example, the name chromium(III) chloride tells you that the chromium ion in the compound is Cr3+. The chloride ion is Cl. For a neutral compound, there must be three chlorine ions for every one chromium ion, so the formula is CrCl3.
When naming a compound that contains a multivalent ion, you must include a Roman numeral to show which charge the ion has.
When naming a compound that contains a multivalent ion, you must include a Roman numeral to show which charge the ion has.
Polyatomic Ions
Limestone is an important industrial mineral that is obtained from quarries in several locations around British Columbia. Limestone is made of an ionic compound called calcium carbonate, CaCO3, which is also the compound that tiny sea animals use to make their shells!
The carbonate ion, CO,2, is composed of carbon and oxygen atoms. An ion that, like carbonate, is composed of two or more atoms is a polyatomic ion-essentially, a charged molecule. Compounds containing polyatomic ions are not binary compounds because they always contain at least three elements. But like binary compounds, compounds containing polyatomic ions are named by writing the name of the positive ion followed by the name of the negative ion.
There are a limited number of polyatomic ions that regularly occur in compounds. You can look up their names, formulas, and charges in a table such as the table below. Notice that the only positively charged polyatomic ion listed is the ammonium ion, NH4.
There are a limited number of polyatomic ions that regularly occur in compounds. You can look up their names, formulas, and charges in a table such as the table below. Notice that the only positively charged polyatomic ion listed is the ammonium ion, NH4.
Names and Formulas of Binary Covalent Compounds
Follow these steps to write the name of a binary covalent compound.
1. The first element in the name and formula of a binary covalent compound is usually the one that is farther to the left on the periodic table.
Example: In carbon monoxide, CO, carbon comes first because carbon is to the left of oxygen on the periodic table.
2. When naming, the suffix -ide is attached to the name of the second element.
Example: Oxygen is changed to oxide in the name carbon monoxide.
3. When naming, prefixes are used to indicate how many atoms of each type are present in one molecule of the compound. Table 2.8 lists the first 10 prefixes. The prefix mono- is used only for the second element in the name. When there is no prefix, mono- is implied, as in carbon monoxide. Also, when mono- comes before -oxide, an "o" is dropped. Thus, you write monoxide, not monooxide.
Example: Using prefixes correctly, the name of CO is carbon monoxide.
Note that when the addition of a prefix results in two vowels appearing together, the vowel at the end of the prefix is usually dropped. The "i" at the end of the prefixes di- and tri- are never dropped, however.
Example: the correct name for PI, is phosphorus triiodide.
To write the formula for a binary covalent compound, write the
element symbols in the order they appear in the name. Add subscripts based on the prefixes used in the name.
1. The first element in the name and formula of a binary covalent compound is usually the one that is farther to the left on the periodic table.
Example: In carbon monoxide, CO, carbon comes first because carbon is to the left of oxygen on the periodic table.
2. When naming, the suffix -ide is attached to the name of the second element.
Example: Oxygen is changed to oxide in the name carbon monoxide.
3. When naming, prefixes are used to indicate how many atoms of each type are present in one molecule of the compound. Table 2.8 lists the first 10 prefixes. The prefix mono- is used only for the second element in the name. When there is no prefix, mono- is implied, as in carbon monoxide. Also, when mono- comes before -oxide, an "o" is dropped. Thus, you write monoxide, not monooxide.
Example: Using prefixes correctly, the name of CO is carbon monoxide.
Note that when the addition of a prefix results in two vowels appearing together, the vowel at the end of the prefix is usually dropped. The "i" at the end of the prefixes di- and tri- are never dropped, however.
Example: the correct name for PI, is phosphorus triiodide.
To write the formula for a binary covalent compound, write the
element symbols in the order they appear in the name. Add subscripts based on the prefixes used in the name.
