Writing chemical formulas from compound names

So far we have started with the chemical formula of a compound and decided on its systematic name. Being able to reverse the process is also important. Often a laboratory procedure describes a compound by name, but the label on the bottle in the lab shows only the formula of the chemical it contains. It is essential that you are able to get the formula of a compound from its name. In fact, you already know enough about compounds to do this. For example, given the name calcium hydroxide, you can write the formula as Ca(OH)2 because you know that calcium forms only Ca ions and that, since hydroxide is OH, two of these anions are required to give a neutral compound. Similarly, the name iron(ll) oxide implies the formula FeO, because the Roman numeral 11 indicates the presence of the cation Fe and the oxide ion is 0 . 

Frankland discovered the fundamental principle of valency—the combining power of atoms to form compounds. He gave the chemical bond its name and popularized the notation we use today for writing chemical formulas. He codiscovered helium, helped found synthetic organic and structural chemistry, and was the father of organometallic chemistry. He was also the first person to thoroughly analyze the gases from different types of coal and—dieters take note—the first to measure the calories in food. 

This was not really a practical recommendation. As mentioned earlier, almost all the agents we tested had no medical name. Had we told the volunteer he had just ingested (l-methyl-4-piperidyl) alpha-cyclobutylmandelate, how much better informed would he be Furthermore, since many chemical sfructures were classified, writing down specific information about them might jeopardize security (e.g., an enemy could see the chemical name and become aware of the Army s interest in the compound). Finally, no benefit was likely to come from a former volunteer telling his doctor the name of a mysterious chemical formula he had once received. 

When writing a chemical formula, you learned that you write the metal element first. Similarly, the metal comes first when naming a chemical compound. For example, sodium chloride is formed from the metal sodium and the non-metal chlorine. Think of other names you have seen in this chapter, such as beryllium chloride, calcium oxide, and aluminum oxide. In each case, the metal is first and the non-metal is second. In other words, the cation is first and the anion is second. This is just one of the rules in chemical nomenclature the system that is used in chemistry for naming compounds. 

One of the most important requirements of chemistry is communicating information to others. Chemists discuss compounds by using both chemical formulas and names. The chemical formula and the name for the compound must be understood universally. Therefore, a set of rules is used in the naming of compounds. This system of naming allows everyone to write a chemical formula when given a compound name and to name the compound from a given chemical formula. 

Now let s go the other way and convert from systematic names to chemical formulas. The first step in writing formulas when given the systematic name of a binary covalent compound is to recognize the name as representing a binary covalent compound. It will have one of the following general forms. 

Follow these steps for writing formulas for binary covalent compounds when you are given a systematic name. Notice that they are the reverse of the steps for writing names from chemical formulas. 

As we noted earlier, chemists have established different sets of rules for writing the names and formulas of different types of chemical compounds, so the first step in writing a name from a chemical formula is to decide what type of compound the formula represents. A chemical formula for an ionic compound will have one of the following forms. 

Before you can write a chemical formula from the name of a compound, you need to recognize what type of compound the name represents. For binary ionic compounds, the first part of the name is the name of a metallic cation. This may include a Roman numeral in parentheses. The anion name starts with the root of the name of a nonmetal and ends with -ide. 

Write formulas for and name the binary hydrogen compounds of the second-period elements (Li to F). Describe how the physical and chemical properties of these compounds change from left to right across the period. 

Acid Names from Anion Names Acids are an important group of hydrogen-containing compounds that have been used in chemical reactions for centuries. In the laboratory, acids are typically used in water solution. When naming them and writing their formulas, we consider them as anions connected to the number of hydrogen ions (H" ) needed for charge neutrality. The two common types of acids are binary acids and oxoacids ... 

Note in some of fhe following problems, you will need to write a chemical formula from the name of the compound. It may help to review Chapter 4. 

Because chemists around the world need to be able to communicate with one another, they have developed a set of rules for naming compounds. Using this standardized naming system, you can write a chemical formula from a compound s name and name a compound given its chemical formula. 

Many ionic compounds contain either aluminum (a Group 3A metal) or a metal from Group lA or Group 2A and a nonmetal—oxygen, nitrogen, or a halogen (Group 7A). Write the chemical formulas and names of all the binary compounds that can result from such combinations. 

In a chemical formula, element symbols and, often, numerical subscripts show the type and number of each atom in the smallest unit of the substance. In this section, you ll learn how to write the names and formulas of ionic and simple covalent compounds, how to calculate the mass of a compound from its formula, and how to visuahze molecules with three-dimensional models. 

Write the formula and name of the compound formed from the following ionic interactions (a) The 2-1- ion and the 1 — ion are both isoelectronic with the atoms of a chemically unreactive Period 4 element, (b) The 2H- ion and the 2— ion are both isoelectronic with the Period 3 noble gas. (c) The 2-1- ion is the smallest with a filled d subshell the anion forms from the smallest halogen, (d) The ions form from the largest and smallest ion-izable atoms in Period 2. 

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