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In the next lesson, we will review the rules of chemical nomenclature and why we use them. At the end of this lesson, you should be able to name most inorganic chemicals, compound, or material.
We have just covered the materials having to do with the atomic structure, the stability of atoms, and the most useful way to demonstrate electron distribution, the Lewis dot diagram. We also synergized these concepts to help understand the important trends of chemical properties on the periodic table, making it an important and powerful tool.
When elements combine to form compounds, the resulting substances have new chemical and physical properties. For example:
Chemists use a shorthand notation for easily symbolizing the ratio of atoms to one another. Each symbol begins with a capital letter. Some, but not all, have additional lowercase letters. For example:
The order of the symbols usually follows the order on the table, that is, the one closest to the left on the table is the one written first in a compound.
Naming compounds is a systematic process. The International Union of Pure and Applied Chemistry (IUPAC) is an organization dedicated to making clear and consistent rules for naming and solving problems of common language for complex chemical compounds. Since every substance has its own set of properties, it is very important to have such a consistent naming system. Without these naming consistencies, the combinations and permutations of different compounds would exceed our ability to realistically name or even discuss them.
Generally, the binary (two different elements) ionic compounds are named with the element farthest to the left on the table first (which is usually the least electronegative), and the element further to the right, second. Using the previous example, sodium chloride follows this idea. Or you can say that the most metallic element comes first and the least metallic element comes second. Iron oxide (commonly known as rust) is an example of a compound where you might recognize the metal as the first part of the name and the non-metal as the second part. In both cases, the second part of the name has a different ending (-ide). Using this rule, what would you call a compound formed from sulfur and aluminum? If you immediately thought aluminum sulfide you would be right. The single negative element always ends in “-ide”.
What is the name of the binary ionic compound made from two atoms of chlorine and one atom of barium?
The correct answer is C, barium chloride, since barium is a metal and chlorine is a non-metal. D is incorrect because you do not change the suffix of an element to match its compound material. Some elements (transitional elements) have more than one common oxidation state and the IUPAC has recommended that these elements include a Roman numeral to indicate their oxidation state. For example, a more correct name for rust is iron III oxide, to indicate that iron is in the +3 oxidation state in that compound. The old naming system would call that compound ferric oxide. Cupric oxide would indicate copper II oxide. To avoid confusion, the new naming system identifies the oxidation state by using a Roman numeral in the name.
Ternary compounds often contain oxygen along with two other elements. Oxygen is the most commonly reacted element on the table and can bond with just about anything. Often oxygen will be found in what is known as a polyatomic ion, or a group of non-metals bonded to non-metals, that exist as a very stable charged complex. An example of this is a sulfate ion which is made of one sulfur atom and four oxygen atoms (SO4-2). If aluminum bonds to sulfate, the resulting formula would look like this: Al2(SO4)3. Because aluminum’s oxidation number is +3 and sulfate’s oxidation number is -2, there are three sulfate ions for every two aluminum atoms for an algebraic sum to equal zero. (3 · – 2 = – 6 and 2 · +3 = + 6). There are many types of polyatomic ions and most of them include oxygen. The naming of these compounds follows the same pattern as a binary compound, which is the name of the positive element, aluminum, first, then the name of the negative ion, sulfate, second.
What is the proper name of a compound made from one atom of hydrogen, one atom of carbon, one atom of sodium, and three atoms of oxygen?
The correct answer is D, but the compound (NaHCO3) is also called sodium bicarbonate, or more commonly, baking soda. The other possibilities either do not incorporate all the elements (Na, C, O, and H), or do not follow the nomenclature rules of naming complex compounds whereby the metal is listed first. A major hint is that the carbonate ion (CO3) needs to have its own name independent of the metal and hydrogen that come before it.
Some substances have unique properties when dissolved in water and thus have their own naming system. We refer to these as acids. Because of the nature of the water molecule, there are two pairs of unshared electrons that exist on the oxygen atom. These are perfect for attracting a hydrogen ion that has lost its electron to a strongly electronegative element such as chlorine. Remember that for hydrogen to exist in a stable state it needs two electrons or the same configuration as helium. So in a water solution, the free floating hydrogen ions are attracted to the electron pairs in water molecules. These solutions are responsible for characteristics of acids, like sour taste, low pH, and the ability to change an indicator dye such as litmus from blue to pink.
H+ hydrogen ion (no electrons)
· ·
H : O : water molecule
· ·
H
A hydrogen ion bonded in this way to a water molecule is also known as a hydronium ion.
Naming acids is systematic as well.
There are additional rules for naming acids with different numbers of oxygen atoms. Some theories even label substances as acids that don’t have hydrogen and don’t have to be dissolved in water, but these are not the most common or recognized naming schemes. The IUPAC details these additional naming schemes. The most traditional theory of acids and bases first proposed by Svante August Arrhenius, a Swedish chemist who won the Nobel Prize in 1903, is based on hydrogen ions in water solutions.
Non-metals will often bond to other non-metals in a way where the electrons are shared and separate ions are not formed. These compounds are called molecules and also use a prefix naming system to identify the ratio of atoms which may exist in a variety of proportions. For example,
Prefixes for naming molecules (covalently bonded):
| Mono | 1 | Hexa | 6 |
| Di | 2 | Hepta | 7 |
| Tri | 3 | Octa | 8 |
| Tetra | 4 | Nona | 9 |
| Penta | 5 | Deca | 10 |
Remember, the reason that elements bond with other elements is to form a more stable state and there is a wide variety of possibilities with the 118 elements on the table. Using the most common oxidation numbers based on electron configuration patterns makes the table a useful predictive tool.