Writing Formulas of Ionic Compounds

In order to write a formula for a compound, for example formed by and the absolute values of the charges should be crossed, as shown below. Here, crossing means writing the number of the charge of an ion as a subscript on the other one. 

The sum of the oxidation numbers (valencies) of all elements in a compound is zero. 

carbon dioxide, has one carbon atom and two oxygen atoms in its formula. Such compounds do not require the subscript 1 to specify their single carbon atom. 

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We learned to write formulas of ionic compounds in Chaps. 5 and 6. We balanced the charges to determine the number of each ion to use in the formula. We could not do the same thing for atoms of elements in covalent compounds, because in these compounds the atoms do not have charges. In order to overcome this difficulty, we define oxidation numbers, also called oxidation states. 

For a review of writing formulas of ionic compounds, see Chapter 4. 

When writing formulas of ionic compounds, the subscript of the cation is numerically equal to the charge of the anion, and the subscript of the anion is numerically equal to the charge on the cation. If the charges of the cation and anion are numerically equal, then no subscripts are necessary. Charges of conunon cations and... 

When writing equations for acid-base reactions, write the formula of the salt using the procedure for writing formulas of ionic compounds given in Section 5.5. 

Be sure you use parentheses correctly in writing formulas of ionic compounds. They enclose polyatomic ions used more than once, but never a monatomic ion. Examples are BaClj, not Ba(Cl)2 Ba(OH)2, not BaOH2 but NaOH, not Na(OH). 

Complete the formula-writing exercise in Table 6.13 on page 170. When you have developed your skill in writing formulas of ionic compounds, test it by writing the formulas of the compounds in Questions 33 through 38. 

This section explains why the formulas of ionic compounds are what they are. Writing formulas of ionic compounds is discussed in Section 6.8. You must account for all of the electrons in all of the atoms in the formula unit of an ionic compound. 

When writing formulas of ionic compounds, the positive ion is always written first and then the negative ion. Subscripts are used to indicate the numbers of ions that are in the compound. 

In writing the formulas of ionic compounds, make sure the subscripts are in the lowest ratio of whole numbers. 

The charges on the ions allow us to deduce the formula from the name of a compound, even though the numbers of each type of ion are not stated in the name. Writing formulas for ionic compounds requires deducing how many of each type of ion must be present to have a neutral compound (see Section 5.2). 

In writing formulas for ionic compounds from their names, we must remember the rules from Chapter 5. Be sure to balance the number of positive and negative charges The charges on the cations are implied for some cations (the constant type) and stated explicitly in the name for the others. The charge on a monatomic anion is equal to the group number minus 8 (see Section 5.2). 

In Chapter 5, we learned to write formulas for ionic compounds from the charges on the ions and to recognize the ions from the formulas of the compounds. For example, we know that aluminum chloride is AICI3 and that VCI2 contains ions. We cannot make comparable deductions for covalent compounds because they have no ions there are no charges to balance. To make similar predictions for species with covalent bonds, we need to use the concept of oxidation number, also called oxidation state. A system with some arbitrary rules allows us to predict formulas for covalent compounds from the positions of the elements in the periodic table and also to balance equations for complicated oxidation-reduction reactions. 

Seawater contains many dissolved substances, mostly dissolved sodium chloride. In Chapter 4, you learned that sodium chloride is an ionic compound. Another ionic compound found dissolved in seawater is magnesium chloride. Some common ionic compounds used in everyday life are potassium chloride, a salt substitute used by people avoiding sodium for health reasons potassium iodide, added to table salt to prevent iodine deficiency and sodium fluoride, added to many toothpastes to strengthen tooth enamel. You will learn how to use the language of chemistry to name and write the formulas of ionic compounds. 

Formulas are part of the language that is used to communicate information about substances. As a first step in studying this new language, you will learn how to name and write formulas for ionic compounds. 

Writing formulas for ionic compounds that include polyatomic ions is done in the same way formulas are written for binary compounds. The polyatomic ions are treated as single units that bear a charge. The goal is to get the right ratio of cation to anion so that an overall electrically neutral combination is obtained. The same rules used for binary compounds apply here, with one modification ... 

We normally write the empirical formulas of ionic compounds without showing the charges. The + and — are shown here to emphasize the transfer of electrons. 

Answer We use the electroneudality as our guide in writing formulas for ionic compounds. According to Figure 9.1, the Lewis dot symbols of A1 and O are... 

Formulas for binary ionic compounds In the chemical formula for any ionic compound, the symbol of the cation is always written first, followed by the symbol of the anion. Subscripts, which are small numbers to the lower right of a symbol, represent the number of ions of each element in an ionic compound. If no subscript is written, it is assumed to be one. You can use oxidation numbers to write formulas for ionic compounds. Recall that ionic compounds have no charge. If you add the oxidation number of each ion multiplied by the number of these ions in a formula unit, the total must be zero. 

Write formulas for ionic compounds composed of the following ions. 

Write the empirical formulas of ionic compounds, given the chaiges of their component ions. (Section 2.7)... 

Using the Stock system, the ferrous ion and the ferric ion are iron(II) and iron(III), respectively, so ferrous chloride becomes iron(II) chloride and ferric chloride is called iron(III) chloride. In keeping with modem practice, we will use the Stock system of naming compounds in this textbook. Examples 0.3 and 0.4 illustrate how to name and write formulas for ionic compounds based on the information given in Table 0.3. 

Rules for Writing Formuias There are three rules for writing formulas of coordination compounds (the first two are the same as those for the formula of any ionic compound) ... 

Chapter 6, Ionic and Molecular Compounds, describes how atoms form ionic and covalent bonds. Chemical formulas are written, and ionic compounds— including those with polyatomic ions—and molecular compounds are named. An introduction to the three-dimensional shape of carbon molecules provides a basis for the shape of organic and biochemical compounds. Organic chemistry is introduced with the properties of inorganic and organic compounds and condensed structural formulas of alkanes. Section 6.1 is now tilled Ions Transfer of Electrons, 6.2 is titled Writing Formulas for Ionic Compounds, 6.3 is... 

C03-0063. Which of the following compounds are ionic Write the formula of each compound, (a) hydrogen fluoride (b) calcium fluoride (c) aluminum sulfate (d) ammonium sulfide (e) sulfur dioxide and (f) carbon tetrachloride. 

C03-0064. Which of the following compounds are ionic Write the formula of each compound, (a)... 

Writing the formula for ionic compounds requires us to know the charge of the cation and anion making up the ionic compound. Information on the charge of common ions can be obtained from the periodic table. More will be said about this in Chapter 7, but for now, a few basic rules will help us write the formulas for simple ionic compounds ... 

Each of the following pairs of elements will react to form an ionic compound. Write the formula of each compound formed, and give its name. 

For transition metals, the lanthanides, and the actinides, no such simple rule exists. If we accept the ions charges as chemical facts, we can still write the empirical formulas for ionic compounds so that the net (overall) charge is zero. If we had Fe2+ and O2-, the compound would require a minimum of one of each of the elements for a neutral formula, FeO, whereas Fe3+ and O2- would have the formula Fe2C>3. 

The formula for an ionic compound actually represents the simplest ratio of ions within a crystal. It is important to remember that the formulas you write for the test must represent the simplest ratio of ions. There are two main ways to write the formulas for ionic compounds. The first method uses conservation of charge, while the second is a shortcut method often called the crisscross method. 

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