Polyatomic ions ionic compound formulas

Compounds Formed from Polyatomic Ions Ionic compounds in which one or both of the ions are polyatomic are very common. Table 2.5 gives the formulas and the names of some common polyatomic ions. Remember that the polyatomic ion stays together as a charged unit. The formula for potassium nitrate is KNO3 each balances one N03. The formula for sodium carbonate is Na2C03 two Na balance one CO-. When two or more of the same polyatomic ion are... 

When naming ionic compounds containing polyatomic ions, we write the positive ion, usually a metal, first, and then we write the name of the polyatomic ion. It is important that you learn to recognize the polyatomic ion in the formula and name it correctly. As with other ionic compounds, no prefixes are used. 

We name ionic compounds that contain a polyatomic ion in the same way as other ionic compounds, except that we use the name of the polyatomic ion whenever it occurs. Table 3.5 lists conunon polyatomic ions and their formulas. For example, NaN02 is named according to its cation, Na (sodium), and its polyatomic anion, NO2 (nitrite). Its full name is sodium nitrite. 

Crafting names and formulas for ionic and molecular compounds Handling polyatomic ions Talking about acids... 

To complicate your life further, polyatomic ions sometimes occur multiple times within the same ionic compound. How do you specify that your compound has two sulfate ions in a way that makes visual sense Put the entire polyatomic ion formula in parentheses and then add a subscript outside the parentheses to indicate how many such ions you have, as in (S04 ")2-... 

Ionic compounds containing polyatomic ions (Section 2.8) are named in the same way as binary ionic compounds First the cation is identified and then the anion. For example, Ba(N03)2 is called barium nitrate because Ba2+ is the cation and the N03 polyatomic anion has the name nitrate. Unfortunately, there is no systematic way of naming the polyatomic ions themselves, so it s necessary to memorize the names, formulas, and charges of the most common ones listed in Table 2.3. The ammonium ion (NH4+) is the only cation on the list all the others are anions. 

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. 

Compounds that contain polyatomic ions Many ionic compounds contain polyatomic ions, which are ions made up of more than one atom. Table 8-6 lists the formulas and the charges for several polyatomic ions. 

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. 

How can you determine the formula unit for an ionic compound containing a polyatomic ion Chemists use a naming system called the Stock System, after the German chemist Alfred Stock. Let s consider the compound formed from the ammonium ion and the chloride ion. 

The formulas of the chemical compounds are no accident. There is an NaCl, but no NaCl2 there is a Cap2, but no CaF. On the other hand, certain pairs of elements form two, or even more, different compounds, e.g. C]u20, CuO N2O, NO, NO2. In the case of ionic compounds the relative number of positive and negative ions in a formula is governed simply by the rule of electrical neutrality. In covalent compounds, or within polyatomic ions (like NO ), structures are formed by covalent bonds (i.e., electron sharing). A hierarchy of covalent bonding theories exists, of which the simplest, the drawing of Lewis structures, is emphasized in this and in most elementary texts. 

Metal-polyatomic ion Polyatomic ions can take the place of monatomic anions, so formulas that contain a symbol for a metallic element and the formula for a polyatomic ion represent ionic compounds. For example, NaN03 (in solid rocket propellants) and 7 2(504)3 (a foaming agent in fire foams) represent ionic compounds. 

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... 

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. 

Calcium phosphate, Ca3(P04)2, is an ionic compound that contains monatomic calcium ions, Ca, and polyatomic phosphate ions, P04 . The oxidation number of each phosphorus atom can be determined in two ways. The following shows how it can be done considering the whole formula. 

An ionic compound that contains 10.279% calcium, 65.099% iodine, and 24.622% oxygen is used in deodorants and in mouthwashes. What is the empirical formula for this compound What do you think its chemical name is (Consider the possibility that this compound contains more than one polyatomic ion.)... 

Formulas of Ionic Compounds with Polyatomic Ions... 

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 ... 

Example 1 Find the molar mass of (NH4)2S04. Counting all the atoms in the formulas of some ionic compounds requires care. This is because many ionic compounds contain multiple polyatomic ions. The formula of ammonium sulfate, (NH4)2S04, is made up of three polyatomic ions, two ammonium ions, NH4+, and one sulfate ion, S04z . There is a total of 15 atoms in the formula unit, and each atom contributes to the formula mass of the compound. Two NH4+ ions = 2 N atoms and 8 H atoms one S042 ion = 1 S atom and 4 O atoms. The sum of the atomic masses can be symbolized ... 

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