Compounds That Contain Ions

For Groups 1,2, and 3, the charges of the cations equal the group numbers. 

In contrast to the Group 1,2, and 3 metals, most of the many transition metals form cations with various positive charges. For these elements there is no easy way to predict the charge of the cation that will be formed. 

Note that metals always form positive ions. This tendency to lose electrons is a fundamental characteristic of metals. Nonmetals, on the other hand, form negative ions by gaining electrons. Note that the Group 7 atoms all gain one electron to form 1 - ions and that all the nonmetals in Group 6 gain two electrons to form 2 ions. 

OBJECTIVE To learn how ions combine to form neutral compounds. 

Melting means that the solid, where the ions are locked into place, is changed to a liquid, where the ions can move. 

A substance containing ions that can move can conduct an electric current. 

Dissolving NaCI causes the ions to be randomly dispersed in the water, allowing them to move freely. Dissolving is not the same as melting, but both processes free the ions to move. 

An ionic compound cannot contain only anions or only cations, because the net charge of a compound must be zero. 

The net charge of a compound (zero) is the sum of the positive and negative charges. 

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Compounds that contain ions of alkali metals (e.g., K+ or Na+). 

If we refer to the general solubility rules, in this case, we are not really able to identify the precipitate, because there seem to be conflicting trends. We notice that compounds that contain ions of alkali metals tend to be soluble, which would seem to suggest that the sodium chlorate is probably not the precipitate, but we also read that compounds that contain halogens also tend to be soluble, which would seem to let the lead (II) iodide off the hook How is it possible for us to have a solid precipitate and then have no suspect ... 

The most important concept for this question from Section 3.15(c) Solubility is the general rule that compounds that contain ions with widely different radii are more soluble in water than compounds containing ions with similar radii. The six-coordinate radii of Na" and K are 1.02 and 1.38 A, respectively (see Table 1.4), whereas the thermochemical radius of the perchlorate ion is 2.36 A (see Table 3.10). Therefore, because the radii of Na and CIO4 differ more than the radii of K and CIO4", the salt NaC104 should be more soluble in water than KCIO4. 

Compounds That Contain Ions 101 Chapter Review 105... 

Because acetylene is a far weaker acid than water and alcohols these substances are not suitable solvents for reactions involving acetylide ions Acetylide is instantly converted to acetylene by proton transfer from compounds that contain —OH groups... 

First the peak for the molecular ion M for all compounds that contain only car bon hydrogen and oxygen has an m z value that is an even number The presence of a nitrogen atom m the molecule requires that the m z value for the molecular ion be odd An odd number of nitrogens corresponds to an odd value of the molecular weight an even number of nitrogens corresponds to an even molecular weight... 

Compounds that contain chlorine, bromine, sulfur, or silicon are usually apparent from prominent peaks at masses 2, 4, 6, and so on, units larger than the nominal mass of the parent or fragment ion. Eor example, when one chlorine atom is present, the P + 2 mass peak will be about one-third the intensity of the parent peak. When one bromine atom is present, the P + 2 mass peak will be about the same intensity as the parent peak. The abundance of heavy isotopes is treated in terms of the binomial expansion (a -I- h) , where a is the relative abundance of the light isotope, b is the relative abundance of the heavy isotope, and m is the number of atoms of the particular element present in the molecule. If two bromine atoms are present, the binomial expansion is... 

The ions in an electrolyte solution can arise in two major ways. They may already be present in the pure compound, as in ionic solids. When such a solid is placed in water, the ions separate and move throughout the solution. However, some compounds that form ions in water are not considered to contain ions when pure, whether in the solid, liquid, or gas phase. Hydrochloric acid, HQ, and sulfuric acid, H2S04, are good examples of the second type of compound. They form molecular liquids (or solids, if cold enough). But in water they form ions HC1 gives hydrogen ion, H+(aq), and chloride ion, G (aq) H2SO ... 

First check to see whether the compounds are ionic or molecular. Many compounds that contain a metal are ionic. Write the symbol of the metal first, followed by the symbol of the nonmetal. The charges on the ions are determined as shown in Examples C.l and C.2. Subscripts are chosen to balance charges. Compounds of two nonmetals are normally molecular. Write their formulas by listing the symbols of the elements in the same order as in the name, with subscripts corresponding to the Greek prefixes used. 

An acid is a compound that contains hydrogen and reacts with water to form hydrogen ions. 

Many complexes and coordination compounds exist as isomers, compounds that contain the same numbers of the same atoms but in different arrangements. For example, the ions shown in (13a) and (13b) differ only in the positions of the Cl ligands, but they are distinct species, because they have different physical and chemical properties. Isomerism is of more than academic interest for example, anticancer drugs based on complexes of platinum are active only if they are the correct isomer. The complex needs to have a particular shape to interact with DNA molecules. 

Arrhenius acid A compound that contains hydrogen and releases hydrogen ions (H+) in water. Examples HC1 CH5COOH but not CH4. 

H2—He at 8.5 5. This ion is an example of a homoaromatic compound, which may be defined as a compound that contains one or more sp -hybridized carbon atoms in an otherwise conjugated cycle. °... 

Many ionic compounds contain what used to be referred to as water of crystallization . For example, magnesium chloride can exist as a fully hydrated salt which was formerly written MgCla.bHjO, but is more appropriately written Mg(OH2)eCl2, since the water molecules occupy coordination sites around the magnesium ions. This is typical. In most compounds that contain water of crystallization, the water molecules are bound to the cation in an aquo complex in the manner originally proposed by Alfred Werner (1866-1919) in 1893 (Kauffman, 1981). Such an arrangement has been confirmed in numerous cases by X-ray diffraction techniques. 

Suppose you have different compounds that contain Cl ions. 

There is another use of the Kapustinskii equation that is perhaps even more important. For many crystals, it is possible to determine a value for the lattice energy from other thermodynamic data or the Bom-Lande equation. When that is done, it is possible to solve the Kapustinskii equation for the sum of the ionic radii, ra + rc. When the radius of one ion is known, carrying out the calculations for a series of compounds that contain that ion enables the radii of the counterions to be determined. In other words, if we know the radius of Na+ from other measurements or calculations, it is possible to determine the radii of F, Cl, and Br if the lattice energies of NaF, NaCl, and NaBr are known. In fact, a radius could be determined for the N( )3 ion if the lattice energy of NaNOa were known. Using this approach, which is based on thermochemical data, to determine ionic radii yields values that are known as thermochemical radii. For a planar ion such as N03 or C032, it is a sort of average or effective radius, but it is still a very useful quantity. For many of the ions shown in Table 7.4, the radii were obtained by precisely this approach. 

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