Polyatomic ion

Ions aren t always monoatomic, composed of just one atom. Ions can also be polyatomic, composed of a group of atoms. For example, take a look at Table 6-3. Notice an3rthing about the Mercury(I) ion Its ion symbol, Hg2 shows that two mercury atoms are bonded together. This group has a 2+ charge, with each mercury cation having a 1+ charge. The mercurous ion is classified as a polyatomic ion. 

Polyatomic ions are treated the same as monoatomic ions (see Naming Ionic Compounds, later in this chapter). Table 6-4 lists some important polyatomic ions. 

The symbol for the sulfate ion, SO/, indicates that one sulfur atom and four oxygen atoms are bonded together eind that the whole polyatomic ion has two extra electrons. 

Polyatomic Ions.—Maier et have presented a summary of some studies of the radiative and non-radiative relaxation processes of the molecular cations CO (B 2 ), ClCN (B n), H—C C—C C—and 1,2,4,5- 

F4H2(B B, ). They measured fluorescence quantum yields and lifetimes using photoelectron-photon coincidence techniques and determined laser- 

Deliarvey, B. Leyh, M. Desouter-Leconte, J. C. Lorquet, J. Delwiche, and M. J. Hubin- 

Vibrational state distributions of HF(n = 0—12) and DF(u = 0—17) produced in the reactions of SFe with H and D atoms have been measured by Hamilton ef The distributions were found to show some vibrational 

The unimolecular decomposition of C6H5Cr has been studied by analysing the distorted C5H5 peak shape observed in a TOP mass spectrometer following MPI of jet-cooled chlorobenzene. The analysis provided values for the specific reaction rate constants, k(E), which agreed well with the results of previous studies, validating the MPI/TOF m.s. technique as a means for investigating ion decomposition rates. 

Polyatomic Ions Polyatomic ions are formed from two or more nonmetal atoms that are bonded together in a way that results in a net electrical charge. The subtleties of predicting the charge and formula of these ions is fairly involved, and you should content yourself with learning the ions listed in Table 2.1. 

Some of these ions merit special comment. Some ions, like S04-2 and S03 2, differ only in a single oxygen atom. In these cases, the ion with the larger number of oxygen atoms is given the -ate suffix, while the ion with the smaller number of oxygen atoms is given the -ite suffix. 

Some of the ions, for example HC03, contain a hydrogen atom. They are formed by combining the parent ion (C032- in this case) with an acid (H+ ion). 

These half acid salts can be named in two ways. The systematic way is to simply name both components HC03 is formed from a hydrogen ion plus a carbonate ion, and is, therefore, named hydrogencarbonate. The common, if less systematic, approach is to call this the bicarbonate ion. 

Write the name and formula for an Ionic compound containing a polyatomic ion. 

An ionic compound may also contain a polyatomic ion as one of its cations or anions. A polyatomic ion is a gronp of covalently bonded atoms that has an overall ionic charge. 

Most polyatomic ions consist of a nonmetal such as phosphorus, sulfur, carbon, or nitrogen covalently bonded to oxygen atoms. 

FIGURE 6.3 Many products contain polyatomic ions, which are groups of atoms that have an ionic charge. 

The names of the most common negatively charged polyatomic ions end in ate such as nitrate and sulfate. When a related ion has one less oxygen atom, the ite ending is used for its name such as nitrite and sulfite. Recognizing these endings will help you identify polyatomic ions in the names of compounds. The hydroxide ion (OH ) and cyanide ion (CN ) are exceptions to this naming pattern. 

19 Write the name for each of the following ionic compounds  

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Infrared Spectra for Molecules and Polyatomic Ions The energy of infrared radiation is sufficient to produce a change in the vibrational energy of a molecule or polyatomic ion (see Table 10.1). As shown in Figure 10.14, vibrational energy levels are quantized that is, a molecule may have only certain, discrete vibrational energies. The energy for allowed vibrational modes, Ey, is... 

In addition to the Zachariasen and radius ratio rules, for oxides the electronegativity of the predominant cation should be between 1.7 and 2.1 (7). If the cation electronegativity is too high, the compound tends to form molecules or discrete polyatomic ions rather than a connected network. For example, CrO satisfies the radius ratio rule, but the highly electronegative Cr ions promote the formation of discrete dichromate(VI) ions, Cr202 , in the presence of other oxides. 

Several ion sources are particularly suited for SSIMS. The first produces positive noble gas ions (usually argon) either by electron impact (El) or in a plasma created by a discharge (see Fig. 3.18 in Sect. 3.2.2.). The ions are then extracted from the source region, accelerated to the chosen energy, and focused in an electrostatic ion-optical column. More recently it has been shown that the use of primary polyatomic ions, e. g. SF5, created in FI sources, can enhance the molecular secondary ion yield by several magnitudes [3.4, 3.5]. 

So far, there have been few published simulation studies of room-temperature ionic liquids, although a number of groups have started programs in this area. Simulations of molecular liquids have been common for thirty years and have proven important in clarifying our understanding of molecular motion, local stmcture and thermodynamics of neat liquids, solutions and more complex systems at the molecular level [1 ]. There have also been many simulations of molten salts with atomic ions [5]. Room-temperature ionic liquids have polyatomic ions and so combine properties of both molecular liquids and simple molten salts. 

The ions dealt with to this point (e.g., Na+, Cl-) are monatomic that is, they are derived from a single atom by the loss or gain of electrons. Many of the most important ions in chemistry are polyatomic, containing more than one atom. Examples include the hydroxide ion (OH-) and the ammonium ion (NH ). In these and other polyatomic ions, the atoms are held together by covalent bonds, for example,... 

In a very real sense, you can think of a polyatomic ion as a charged molecule. ... 

Ionic compounds containing polyatomic ions. Ftitassium dichromate (KjCtjOj, orange), potassium permanganate (KMnOa, very dark purple), and potassium nitrate (KNO3. white). 

Table 2.2 lists some of the polyatomic ions that you will need to know, along with their names... 

Click Coached Problems for a self-study module on polyatomic ions. 

Polyatomic ions, as you have seen (Table 2.2), are given special names. Certain non-metals in Groups 15 to 17 of the periodic table form more than one polyatomic ion containing oxygen (oxoanions). The names of several such oxoanions are shown in Table 2.3. From the entries in the table, you should be able to deduce the following rules ... 

Similar relationships hold for ionic solids containing polyatomic ions (Table 2.2) or transition metal cations (Figure 4.2). 

The concept of oxidation number is used to simplify the electron bookkeeping in redox reactions. For a monatomic ion (e.g., Na+, S2 ), the oxidation number is, quite simply, the charge of the ion (+1, —2). In a molecule or polyatomic ion, the oxidation number of an element is a pseudo-charge obtained in a rather arbitrary way, assigning bonding electrons to the atom with the greater attraction for electrons. 

The sum of the oxidation numbers in a neutral species is 0 in a polyatomic ion, it is equal to the charge of that ion. The application of this very useful principle is illustrated in Example 4.8. 

This chapter is devoted to the covalent bond as it exists in molecules and polyatomic ions. We consider—... 

In the Lewis structure of a molecule or polyatomic ion, valence electrons ordinarily occur in pairs. There are two kinds of electron pairs. 

These examples illustrate the principle that atoms in covalently bonded species tend to have noble-gas electronic structures. This generalization is often referred to as the octet rule. Nonmetals, except for hydrogen, achieve a noble-gas structure by sharing in an octet of electrons (eight). Hydrogen atoms, in molecules or polyatomic ions, are surrounded by a duet of electrons (two). 

Although most of the molecules and polyatomic ions referred to in general chemistry follow the octet rule, there are some familiar species that do not. Among these are molecules containing an odd number of valence electrons. Nitric oxide, NO, and nitrogen dioxide, N02, fall in this category ... 

In this section we apply this model to predict the geometry of some rather simple molecules and polyatomic ions. In all these species, a central atom is surrounded by from two to six pairs of electrons. 

In many molecules and polyatomic ions, one or more of the electron pairs around the central atom are unshared. The VSEPR model is readily extended to predict the geometries of these species. In general—... 

Draw Lewis structures for molecules and polyatomic ions. 

Write the Lewis structures for the following molecules and polyatomic ions. In each case, the first atom is the central atom. 

Give the formula of a polyatomic ion that you would expect to have the same Lewis structure as... 

In each of the following polyatomic ions, the central atom has an expanded octet. Determine the number of electron pairs around the central atom and the hybridization in... 

Follow the directions of Question 55 for the following polyatomic ions. 

Consider the polyatomic ion I065-. How many pairs of electrons are around the central iodine atom What is its hybridization Describe foe geometry of foe ion. 

Polar molecule A molecule in which there is a separation of charge and hence positive and negative poles, 183-185 dipole force, 237 orientation, 183 Polarimeter, 600 Polarity, 184-185 Pollutants, 6 Polyamide, 615-616 Polyatomic ion, 36,39 Polyatomic molecules, 654 Polyester A large molecule made up of ester units, 614-615 Polyethylene, 611-612... 

Some elements—particularly the halogens—form more than two kinds of oxoanions. The name of the oxoanion with the smallest number of oxygen atoms is formed by adding the prefix hypo- to the -ite form of the name, as in the hypochlorite ion, CIO-. The oxoanion with the most oxygen atoms is named with the prefix per- added to the -ate form of the name. An example is the perchlorate ion, C104-. The rules for naming polyatomic ions are summarized in Appendix 3A and common examples are listed in Table D.l. 

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,... 

U 1 Name ions, binary inorganic compounds, oxoacids, compounds with common polyatomic ions, and hydrates, and write their formulas (Toolboxes D.l and D.2, Self-Test D.l, and Examples D.l, D.2, and D.3). 

When an element is part of a compound or a polyatomic ion, we assign its oxidation number by using the procedure in Toolbox K.l. 

FIGURE 2.8 A micrograph ot bone, which owes its rigidity to calcium phosphate. The overlay shows part of the crystal structure of calcium phosphate. Phosphate ions are polyatomic ions however, as shown in the inset, they are nearly spherical and fit into crystal structures in much the same way as monatomic ions of charge —3. 

One form of the polyatomic ion I, has an unusual V-shaped structure one I atom lies at the point of the V, with a linear chain of two I atoms extending on each side. The bond angles are 88° at the central atom and 180° at the two atoms in the side chains. Draw a Lewis structure for L that explains its shape and indicate the hybridization you would assign to each nonterminal atom. 

These ideas are speculative only and cannot be considered conclusive until other cases are tested. Unfortunately, information on states of polyatomic ions is meager. Two ions which have been studied are C02 + and CS2 +, both of which have 2w ground states and 22 excited states. It would be interesting to look for ion-neutral reactions having these ions as possible intermediates. 

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