Compound from polyatomic ions

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... 

So far in this chapter we have discussed only binary ionic compounds, which contain ions derived from single atoms. However, many compounds contain polyatomic ions charged species composed of several atoms. For example, ammonium nitrate contains the and N03 ions. 

So far in this chapter we have discussed only binary ionic compounds, which contain ions derived from single atoms. However, many compounds contain polyatomic ions charged species composed of several atoms. For example, ammonium nitrate contains the NH4- and NOs ions. These ions with their opposite charges attract each other in the same way as do the simple ions in binary ionic compounds. However, the individual polyatomic ions are held together by covalent bonds, with all of the atoms behaving as a unit. For example, in the ammonium ion, NH4-, there are four N—H covalent bonds. Likewise the nitrate ion, NOs , contains three covalent N—O bonds. Thus, although ammonium nitrate is an ionic compound because it contains the NH4-and NO3" ions, it also contains covalent bonds in the individual polyatomic ions. When ammonium nitrate is dissolved in water, it behaves as a strong electrolyte like the binary ionic compounds sodium chloride and potassium bromide. As we saw in Chapter 7, this occurs because when an ionic solid dissolves, the ions are freed to move independently and can conduct an elearic current. 

Compounds involving polyatomic ions work exactly the same way. For example, here s the compound made from the ammonium cation and the sulfide anion ... 

The formulas and names of some common polyatomic ions are given in I Table 4.7. From this information, the formulas and names for compounds containing polyatomic ions can be written. The rules are essentially the same as those used earlier for binary ionic compounds. In the formulas, the metal (or ammonium ion) is written first, the positive and... 

Compounds with Polyatomic Ions Acid Names from Anion Names Binary Covalent Compounds Straight-Chain Alkanes Molecular Masses Formulas and Models... 

Step 2 If the compound is an oxoacid, derive the name of the acid from the name of the polyatomic ion that it produces, as in Toolbox D.1. In general,... 

It should not be inferred that the crystal structures described so far apply to only binary compounds. Either the cation or anion may be a polyatomic species. For example, many ammonium compounds have crystal structures that are identical to those of the corresponding rubidium or potassium compounds because the radius NH4+ ion (148 pm) is similar to that of K+ (133 pm) or Rb+ (148 pm). Both NO j and CO, have ionic radii (189 and 185 pm, respectively) that are very close to that of Cl- (181 pm), so many nitrates and carbonates have structures identical to the corresponding chloride compounds. Keep in mind that the structures shown so far are general types that are not necessarily restricted to binary compounds or the compounds from which they are named. 

When naming compounds containing species not on these lists, it may help to find a chemical species on the list from the same family or a polyatomic ion that is similar. 

As we end this section, let us reconsider ionic radii briefly. Many ionic compounds contain complex or polyatomic ions. Clearly, it is going to be extremely difficult to measure the radii of ions such as ammonium, NH4, or carbonate, COs, for instance. However, Yatsimirskii has devised a method which determines a value of the radius of a polyatomic ion by applying the Kapustinskii equation to lattice energies determined from thermochemical cycles. Such values are called thermochemical radii, and Table 1.17 lists some values. 

Ionic compounds consist of positive ions (cations) and negative ions (anions) hence, ionic compounds often consist of a metal and nonmetal. The electrostatic attraction between a cation and anion results in an ionic bond that results in compound formation. Binary ionic compounds form from two elements. Sodium chloride (NaCl) and sodium fluoride (NaF) are examples of binary ionic compounds. Three elements can form ternary ionic compounds. Ternary compounds result when polyatomic ions such as carbonate (C032 ), hydroxide (OH-), ammonium (NH4+), form compounds. For example, a calcium ion, Ca2+, combines with the carbonate ion to form the ternary ionic compound calcium carbonate, CaC03. Molecular compounds form discrete molecular units and often consist of a combination of two nonmetals. Compounds such as water (H20), carbon dioxide (C02), and nitric oxide (NO) represent simple binary molecular compounds. Ternary molecular compounds contain three elements. Glucose ( 12 ) is a ternary molecular compound. There are several distinct differences between ionic and molecular compounds, as summarized in Table 1.2. 

The sizes of polyatomic ions such as NH and SO2 are of interest for the understanding of the properties of ionic compounds such as (NH4)2S04, but the experimental difficulties attending their determination exceed those of simple ions. In addition, the problem of constancy of size from one compound to the next—always a problem... 

Almost simultaneous with the publication of Kossel s paper there appeared a rival electronic theory. The American chemist Lewis introduced the idea of the covalent electron-pair bond. Like Kossel, he was impressed by the apparent stability of the noble gas configuration. He was also impressed by the fact that, apart from many compounds of the transition elements, most compounds when rendered as molecules have even numbers of electrons, suggesting that electrons are usually found in pairs. Lewis devised the familiar representations of molecules and polyatomic ions (Lewis structures, or Lewis diagrams) in which electrons are shown as dots (or as noughts and crosses) to show how atoms can attain noble gas configurations by the sharing of electrons in pairs, as opposed to complete transfer as in Kossel s theory. It was soon apparent from the earliest X-ray studies that Kossel s theory was more appropriate... 

Three-centre bonding is invoked in situations where the o framework cannot be described in terms of two-centre, electron-pair bonds, although it can often be accommodated by postulating resonance of a different type from that usually encountered. Two types of three-centre bond can be distinguished. The first is often postulated in hypervalent molecules/polyatomic ions AB where the central atom exceeds the octet in its Lewis formulation, as an alternative to the use of d orbitals which many chemists find objectionable. The second type occurs where there appear to be insufficient electrons - regardless of the supply of orbitals -to form the requisite number of bonds in a Lewis/VB description. In other words, the first type is postulated where we have an insufficiency of orbitals, and the second where there is a deficiency of electrons compounds containing the latter type are often described as electron-deficient . 

SIMS has become a diverse tool in the study of many different substances other than metals and semiconductors. This part of the paper discusses the secondary ion emission of molecular and polyatomic ions from the surfaces of organic compounds including polymers and biomolecules. 

To review Up to this point you have learned about the nomenclature of compounds formed from positive and negative ions of various kinds single ions, polyatomic ions, and multivalent ions. 

Some compounds contain ions that are made from more than one atom. These ions are called polyatomic ions. (The prefix poly means many. ) Calcium carbonate, CaC03, which is found in chalk, contains one calcium cation and one polyatomic anion called carbonate, C032-. 

We do not really need oxidation numbers when working with compounds of monatomic ions we can use the charges to write formulas, and we can predict the charges from the periodic table or deduce them from the formulas. When working with compounds with covalent bonds and polyatomic ions (which also... 

Oxidation numbers (also called oxidation states) are used as a sort of bookkeeping method for keeping track of the electrons in polyatomic ions or compounds that have covalent bonds. (For monatomic ions, the charge on the ions works just as well.) Oxidation number is defined as the number of electrons in a free atom minus the number controlled by that atom in the compound. The control of electrons in a covalent bond is assigned to the more electronegative atom of the bond. Eight simple rules can be used to determine the oxidation number of an element from the formula of its compound or ion (Section 16.1). 

An interesting sort of hybrid of ionic and covalent molecules can be found in salts of polyatomic ions. Polyatomic ions are charged groups that contain several different types of atomic nuclei— such as COj ", an ion that is familiar to us from our baking soda demonstrations. Baking soda is sodium bicarbonate, which is NaHCOj. Another polyatomic ion that we have dealt with, although not explicitly until now, is the sulfate ion, SO . As may be recalled, the superscript 2-, read two minus, indicates that the ion has a minus two charge. Copper sulfate, the compound that forms the lovely blue-colored solutions we have used in several demon-... 

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. 

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. 

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