Chemical formulas polyatomic

In a chemical formula, polyatomic ions are placed inside parentheses when using a subscript. 

There are many different polyatomic anions, including several that are abundant in nature. Each is a stable chemical species that maintains its stmcture in the solid state and in aqueous solution. Polyatomic anions are treated as distinct units when writing chemical formulas, naming compounds, or drawing molecular pictures. The names, formulas, and charges of the more common polyatomic anions are listed in Table 3-4. You should memorize the common polyatomic ions because they appear regularly throughout this textbook. 

Visualize NH4 NO3. (Always think atoms and molecules.) Ammonium and nitrate are common polyatomic ions whose chemical formulas you should remember. 

Not all bases contain hydroxide, however. For example, Na2C03 is a base, but its name is sodium carbonate. Baking soda, which has a chemical formula of NaHC03, is also a base. The scientific name for baking soda is sodium hydrogen carbonate (hydrogen carbonate is the name of the polyatomic ion). 

Sulfuric acid, on the other hand, is made up of the polyatomic sulfate ion, which has a charge of -2. Because it has a charge of -2, a sulfate ion requires two hydrogen ions (each of which have a charge of+1) to make it stable. Therefore, sulfuric acid is made up of two hydrogen ions and one sulfate ion, and its chemical formula is H2S04. The subscript number two after the symbol for hydrogen... 

When you write a chemical formula that involves polyatomic ions, you treat them just like other ions. You still need to balance charges to form a neutral atom. We re sorry to report that when you re converting from a formula to a name, you can t use any simple rule for naming polyatomic ions. You just have to memorize the entire table of polyatomic ions and their charges. 

A< Ba(Q02)2.Bcirium is an alkaline ecirth metal (Group IIA) and thus has a chcii e of -1-2. You should recognize chlorite as the name of a polyatomic ion. In fact, any anion name that doesn t end in -ide should scream polyatomic ion to you. As Table 6-1 shows, chlorite is ClOj , which reveals that the chlorite ion has a-1 charge. Two chlorite ions cire necessary to neutralize the -1-2 chcirge of a single barium cation, so the chemical formula is Ba(C102)2-... 

You can use valences to write chemical formulas. This method is faster than using Lewis structures to determine chemical formulas. As well, you can use this method for both ionic and covalent compounds. In order to write a chemical formula using valences, you need to know which elements (or polyatomic ions) are in the compound, and their valences. You also need to know how to use the zero sum rule For neutral chemical formulas containing ions, the sum of positive valences plus negative valences of the atoms in a compound must equal zero. 

Use the information in Table 3.4 to write a chemical formula for a compound that contains sodium and each of the following polyatomic ions. 

Write the chemical formulas for the following acids. Then name and write the formulas for the oxoanions that form from each acid. Refer to Chapter 3, Table 3.5, Names and Valences of Some Common Polyatomic Ions, as necessary. 

Structural formula A chemical formula that shows how the atoms of a molecule or polyatomic ion are arranged and the kinds of bonds (single, double on triple). 

Parentheses are used to group polyatomic ions in a chemical formula with a subscript. 

Explain why it is appropriate to group a polyatomic ion in parentheses in a chemical formula, if more than one of that ion is present in the formula. 

The charge given to a polyatomic ion applies to the entire group of atoms. Although an ionic compound containing one or more polyatomic ions contains more than two atoms, the polyatomic ion acts as an individual ion. Therefore, the chemical formula for the compound can be written following the same rules used for a binary compound. 

The tools that you use for this lesson will be one or more oxidation tables. These tables look different in different books, but the information that they contain is the same. Some periodic tables will include oxidation numbers, so your instructor may ask you to work from that. It is probably more likely that your instructor will give you a separate set of tables with oxidation numbers, so I will follow that format in this text. Often, the oxidation numbers are divided into two tables, one for monatomic (singleatom) ions and one for polyatomic (multiple-atom) ions, as shown here. It doesn t matter where you get the information from, as long as you can use the oxidation numbers to write proper chemical formulas. 

In addition to the reference tables, the important thing to remember is that you want to construct chemical formulas with no net apparent charge. This means that you want to combine the elements in a ratio that would result in a net oxidation number of zero. It is also important to note that we will use parentheses if, and only if, we need to multiply a polyatomic ion with a subscript. The use of parentheses seems to be the thing that students have the most trouble with. Let s try several examples together. 

You will often encounter compounds that contain polyatomic ions, and you will simply look up the symbols and oxidation numbers from the second group of oxidation numbers. For example, let s write the proper chemical formula for the compound called calcium carbonate. Use Figures 5-2a and 5-2b to find the symbols and oxidation numbers associated with each ion. 

The success of the preceding scheme for diatomic molecules I7,i8,i , 20,21) ied Hund 22> and Mulliken 23> to apply the same theory to polyatomic molecules. In the beginning, there seemed to be no direct relation between molecular orbitals (MO s) and the bonds in a chemical formula, because MO s normally extend over the whole molecule and are not restricted to the region between two atoms. The difficulty was overcome by using equivalent localized MO s instead of the delocalized ones 24>25>. The mathematical definition of equivalent MO s was given only in 1949 by Lennard-Jones and his coworkers 26.27), but the concept of localization... 

Word equations describe reactants and products, but they are long and awkward and do not adequately identify the substances involved. Word equations can be converted into chemical equations by substituting chemical formulas for the names of compoimds and elements. Recall from Chapter 5 that these formulas can be written by using the oxidation numbers of the elements and the charges of the polyatomic ions. For example, the equation for the reaction of vinegar and baking soda can be written... 

To write the chemical equation, use chemical formulas to replace the names of the reactants and products in the word equation you wrote. Remember to use the oxidation number of an element and the charge on a polyatomic ion to write a correct formula. Then add symbols to represent the physical state of each compound. 

Ammonium-nonmetal or ammonium-polyatomic ion Ammonium ions, NFf4, can take the place of metallic cations in an ionic compound, so chemical formulas that contain the formula for ammonium with either... 

Convert between the names and chemical formulas for common polyatomic ions such as hydroxide, ammonium, acetate, sulfate, nitrate, phosphate, and carbonate. Be sure to check with your instructor to determine which polyatomic ions you will be expected to know for your exams. 

Convert between the names and chemical formulas for the polyatomic anions that are derived from the additions of H+ ions to anions with -2 or -3 charges. For example, H2P02 is dihydrogen phosphate. 

Given a name or chemical formula, tell whether it represents a binary ionic compound, an ionic compound with polyatomic ion(s), a binary covalent compound, a binary acid, or an oxyacid. 

Convert between names and chemical formulas for binary ionic compounds, ionic compounds with polyatomic ion(s), binary covalent compounds, binary acids, and oxyacids. 

Tip-off In this chapter, you may be given a chemical formula for a molecule or polyatomic ion and asked to draw a Lewis structure, but there are other, more subtle tip-olFs that you will see in later chapters. 

Example 4.7 illustrates that when more than one polyatomic ion appears in a chemical formula, parentheses are used to enclose the ion and a subscript is written after the closing parenthesis. Other examples are (NH4)2S04 and Fe3(P04)2-... 

I To indicate more than one polyatomic ion in a chemical formula, place parentheses around the polyatomic ion and use a subscript. 

In the chemical formulas for aluminum nitrate and copper(II) perchlorate, parentheses followed by the appropriate subscript are used because the compounds contain two or more polyatomic ions. 

Write the symbols for the atoms, show which atoms are attached to which, and connect them with a single hond (a dash, representing two electrons). Chemical formulas are often written in the order in which the atoms are connected in the molecule or ion. The formula HCN, for example, tells you that the carbon atom is bonded to the H and to the N. In many polyatomic molecules and ions, the central atom is usually written first, as in C03 and SF4. Remember that the central atom is generally less electronegative than the atoms surrounding it. In other cases, you may need more information before you can draw the Lewis structure. 

Analyze We are given the chemical formula for a polyatomic anion and asked to describe the type of hybrid orbitals surrounding the central atom. 

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